Synthesis, Characterization, and Antimicrobial Evaluation of Mn(II), Fe(II), and Co(II) Complexes of a Pyrrole-Based Thiosemicarbazone Schiff Base

Synthesis, Characterization, and Antimicrobial Evaluation of Mn(II), Fe(II), and Co(II) Complexes of a Pyrrole-Based Thiosemicarbazone Schiff Base | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Synthesis, Characterization, and Antimicrobial Evaluation of Mn(II), Fe(II), and Co(II) Complexes of a Pyrrole-Based Thiosemicarbazone Schiff Base Bashariyya Lawan Abdullahi This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8484646/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract A new Schiff base ligand was synthesized via the condensation of 4-methyl-3-thiosemicarbazide with 1H-pyrrole-2-carboxaldehyde and subsequently coordinated with Mn(II), Fe(II), and Co(II) ions. The ligand and its metal complexes were characterized using FT-IR, UV–Visible spectroscopy, elemental analysis, magnetic susceptibility, molar conductance, and melting/decomposition temperature determination. Infrared spectral shifts of the azomethine ν(C = N) band, together with the appearance of metal–nitrogen and metal–sulfur vibrational bands, confirm coordination through the azomethine nitrogen and thione sulfur atoms. Electronic and magnetic data support a high-spin octahedral geometry for all complexes. The complexes exhibit improved thermal stability and low molar conductance values, indicating non-electrolytic behavior. Antimicrobial evaluation against Staphylococcus aureus , Escherichia coli , Salmonella typhi, Candida albican , Tinea pedis and Aspergillus flavus revealed enhanced activity for the metal complexes relative to the free ligand, highlighting the role of chelation in modulating biological efficacy. Synthesis Schiff base 4-methyl-3-thiosemicarbazide pyrrole-2-carboxaldehyde antimicrobial activity octahedral geometry Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 INTRODUCTION Heterocyclic compounds are a central class of organic molecules in which one or more ring carbon atoms are replaced by heteroatoms such as nitrogen, oxygen, sulfur, or phosphorus. Their unique electronic properties, structural diversity, and functional adaptability underpin their widespread importance in synthetic, medicinal, and coordination chemistry [ 1 ] Heterocycles form the core frameworks of numerous natural products and pharmaceutical agents, and recent drug-development analyses show that most newly approved therapeutics incorporate at least one heterocyclic moiety, underscoring their continued relevance in molecular design Nitrogen- and sulfur-containing heterocycles are particularly significant in coordination chemistry due to their strong donor ability and directional bonding with transition metals. Coordination through these heteroatoms produces complexes with well-defined geometries, tunable electronic structures, and diverse magnetic, redox, and biological properties [ 4 ] [ 5 ] Among such ligands, Schiff bases derived from heteroaromatic aldehydes and amines are especially attractive because of their synthetic accessibility, structural flexibility, and multidentate coordination behavior [ 5 ]). Thiosemicarbazones constitute an important subclass of Schiff base ligands characterized by the presence of azomethine nitrogen and thione sulfur donor sites within the same framework. They are typically synthesized via condensation of thiosemicarbazide or its derivatives with aldehydes or ketones, generating a C = N linkage adjacent to a C = S group under mild reaction conditions [ 6 ] This donor set enables strong chelation, often leading to thermally stable complexes with enhanced biological and physicochemical properties. Following early reports of antibacterial activity, thiosemicarbazones gained prominence after the discovery of their antitubercular and anticancer potential, stimulating extensive research into their metal complexes [ 7 ] Coordination compounds, formed through coordinate covalent bonding between metal ions and ligands, are fundamental to inorganic chemistry. Their structures and properties such as geometry, magnetism, color, and reactivity are governed by the electronic configuration of the metal center and the nature of the coordinating ligands [ 8 ] Transition metals, owing to their partially filled d-orbitals and variable oxidation states, play crucial roles in biological redox processes and modern catalysis, and have become indispensable in medicinal inorganic chemistry [ 9 ] [ 10 ] Thiosemicarbazone ligands exhibit versatile coordination modes, acting as mono-, bi-, or polydentate donors depending on substitution and reaction conditions. Their ability to form stable chelate rings enhances the thermal stability and biological activity of their metal complexes, which frequently display superior antimicrobial, anticancer, antiviral, and antioxidant properties compared to free ligands [ 11 ]; [ 12 ] In addition to biomedical relevance, these complexes find applications in analytical chemistry, sensing, and materials science, highlighting thiosemicarbazones as key ligands at the interface of heterocyclic chemistry, coordination chemistry, and functional materials research. This study aims to synthesize a new heterocyclic thiosemicarbazone Schiff base and its Mn(II), Fe(II), and Co(II) complexes, and to elucidate their coordination modes, structural characteristics, physicochemical properties, and antimicrobial potential in relation to metal chelation. EXPERIMENTAL Materials and Methods All chemicals and solvents were of analytical reagent grade and used as received without further purification. 4-methyl-3-thiosemicarbazide (T33405) and pyrrole-2-carboxaldehyde (P73404) were purchased from Sigma-Aldrich. Ethanol, methanol, diethyl ether, and dimethyl sulfoxide (DMSO) were of analytical grade. All glassware was thoroughly cleaned, rinsed with distilled water, and oven-dried at 110°C prior to use. Weighing was carried out using a Mettler Toledo analytical balance (Model AB54). Melting and decomposition temperatures were determined using a Gallenkamp SMP10 melting point apparatus. Elemental analyses were recorded using Series II CHNS/O 2400 Perkin Elmer. Scheme 1: Synthesis of Thiosemicarbazone and its Metal (II) Complexes Synthesis of the Thiosemicarbazone ligand An ethanolic solution (20 mL) of 4-methyl-3-thiosemicarbazide (1.05 g, 10 mmol) was mixed with an ethanolic solution (20 mL) of pyrrole-2-carboxaldehyde (0.95 g, 10 mmol), followed by the addition of 2–3 drops of glacial acetic acid as catalyst. The reaction mixture was refluxed at approximately 80°C for 4 h and then allowed to cool to room temperature. The resulting precipitate was filtered, washed with diethyl ether, recrystallized from methanol, and dried in a desiccator over anhydrous calcium chloride [ 13 ]. Synthesis of Metal (II) Complexes The metal complexes were prepared by adding a hot ethanolic solution (20 mL) of the ligand (0.73 g, 0.004 mol) dropwise to a hot ethanolic solution (20 mL) of the corresponding metal(II) chloride salt (0.002 mol) under constant stirring. The reaction mixture was refluxed at approximately 80°C for 5 h. After cooling to room temperature, the resulting complexes were filtered, washed with diethyl ether, recrystallized from methanol, and dried in a desiccator over anhydrous calcium chloride [ 13 ].. Molar Conductivity Measurements Molar conductance measurements were carried out at room temperature using a Jenway conductivity meter (Model 4010). Solutions of the metal complexes were prepared in DMSO, and the instrument was calibrated using standard potassium chloride solutions. Magnetic Susceptibility Measurements Magnetic susceptibility measurements were performed at room temperature using a Sherwood magnetic susceptibility balance. The effective magnetic moments were calculated to determine the electronic configuration and geometry of the metal centers. Infrared Spectral Analysis Fourier transform infrared (FT-IR) spectra of the ligand and its metal(II) complexes were recorded in the range 4000–400 cm⁻¹ using a Cary 630 FT-IR spectrometer (Agilent Technologies) to confirm functional group formation and metal–ligand coordination. UV–Visible Spectral Analysis Electronic spectra were recorded at room temperature in the range 200–600 nm using a PerkinElmer Lambda 35 UV–Visible spectrophotometer to study ligand-centered, d–d, and charge-transfer transitions. Determination of Metal Content Approximately 0.20 g of each metal complex was digested with concentrated HNO₃ (5 mL) and HCl (15 mL) and heated to near dryness. The residue was filtered, diluted to 100 mL with deionized water, and analyzed for metal content using atomic absorption spectroscopy (AAS) following reported procedures. Antimicrobial Assay In vitro antimicrobial assays are routinely employed to evaluate the inhibitory potential of chemical compounds against pathogenic microorganisms. Such assays are widely used in clinical diagnostics, pharmaceutical development and research to identify effective antimicrobial agents and monitor resistance patterns. In the present study, the antimicrobial activity of the synthesized thiosemicarbazone ligand and its metal(II) complexes was evaluated using the agar well diffusion technique, which is a reliable and commonly adopted screening method. Preparation of Stock Solution and Working Concentrations Stock solutions of the thiosemicarbazone ligand and its metal(II) complexes were prepared at a concentration of 2000 µg/mL by dissolving 2 mg of each compound in 1 mL of dimethyl sulfoxide (DMSO) in sterile bijou bottles. Working concentrations of 125, 250, 500 and 1000 µg/mL were obtained from the stock solutions by serial dilution, following the procedure reported by [ 14 ] with slight modifications. DMSO was used as the solvent control throughout the study. Preparation of Culture Media and Test Organisms The antimicrobial activity was evaluated against selected pathogenic microorganisms, including Staphylococcus aureus , Escherichia coli , and Salmonella typhi for antibacterial screening, and Candida albican , Tinea pedis and Aspergillus flavus for antifungal screening. The bacterial and fungal isolates were obtained from Aminu Kano Teaching Hospital and identified at the Department of Microbiology, Bayero University, Kano. Mueller–Hinton agar (MHA) was used for antibacterial studies, while Potato Dextrose Agar (PDA) was employed for antifungal studies. The media were prepared according to the manufacturer’s instructions by dissolving 48 g of MHA and 39 g of PDA separately in 1000 mL of distilled water, followed by sterilization in an autoclave at 121°C for 15 minutes. The molten media were poured into sterile Petri dishes and allowed to cool to approximately 45°C. Wells of 6 mm diameter were made at equidistant positions using a sterile cork borer. The test organisms were standardized using 0.5 McFarland standard, as described by Usman and [ 15 ], to ensure uniform microbial density. In vitro Antibacterial Activity The antibacterial activity of the thiosemicarbazone ligand and its metal(II) complexes was evaluated against Staphylococcus aureus , Escherichia coli , and Salmonella typhi using the agar well diffusion method. Fresh bacterial suspensions were uniformly swabbed onto the surface of solidified Mueller–Hinton agar plates. Aliquots of the prepared test solutions at concentrations of 125, 250, 500 and 1000 µg/mL were introduced into the wells. The plates were incubated at 37°C for 24 hours, after which the zones of inhibition were measured in millimeters using a vernier caliper. Ciprofloxacin was used as the positive control, while DMSO served as the negative control. Antibacterial activity was assessed by comparing the inhibition zones of the test compounds with those of the standard drug. In vitro Antifungal Activity The antifungal activity of the ligand and its metal(II) complexes was investigated against Candida albican , Tinea pedis and Aspergillus flavus using the agar well diffusion technique. Standardized fungal suspensions were swabbed onto the surface of solidified Potato Dextrose Agar plates. Test solutions of the compounds at concentrations of 125, 250, 500 and 1000 µg/mL were dispensed into the wells. The plates were incubated at 37°C for 48 hours, after which zones of complete inhibition were measured in millimeters. Ketoconazole was employed as the positive control, while DMSO served as the negative control. Antifungal activity was determined by comparing the inhibition zones produced by the test compounds with those of the standard antifungal agent. RESULTS AND DISCUSSION The tables below present the results obtained from the physicochemical analysis, spectral characterization, and in-vitro antimicrobial evaluation of the thiosemicarbazone and its complexes. Table 1 Physical properties and percentage yields of the thiosemicarbazone ligand and its metal (II) complexess Compounds Color Melting point (⁰C) Decomposition Temperature (⁰C) Percentage Yield (%) Thiosemicarbazone Light brown 160 - 66.6 [Mn(L) 2 Cl 2 ].2H 2 O Cream - 207 64.0 [Fe(L) 2 Cl 2 ].3H 2 O Coffee Brown - 220 62.1 [Co(L) 2 Cl 2 ].2H 2 O Dark brown - 228 80.5 L = C 7 H 11 N 4 S Table 2 Molar conductance values of Mn(II), Fe(II), and Co(II) complexes in DMSO (1 × 10⁻³ mol dm⁻³). Complex Concentration Moldm − 3 Specific Conductance Ohm − 1 cm − 1 Molar Conductance Ohm − 1 cm 2 mol − 1 [Mn(L) 2 Cl 2 ].2H 2 O 1.0 × 10 − 3 13.50 × 10 − 6 13.5 [Fe(L) 2 Cl 2 ].3H 2 O 1.0 × 10 − 3 14.4 × 10 − 6 14.4 [Co(L) 2 Cl 2 ].2H 2 O 1.0 × 10 − 3 19.5 × 10 − 6 19.5 L = C 7 H 11 N 4 S Table 3 Magnetic susceptibility data and proposed geometries of the thiosemicarbazone metal(II) complexes. Compound Xg(erg.c − 2 g − 1 ) Xm(erg.c − 2 mol − 1 ) µ eff (BM) n Geometry Property [Mn(L) 2 Cl 2 ].2H 2 O 2.834 × 10 − 5 1.495 × 10 − 2 5.97 5 Octahedral Paramagnetic [Fe(L) 2 Cl 2 ].3H 2 O 1.97 × 10 − 5 1.086 × 10 − 2 5.09 4 Octahedral Paramagnetic [Co(L) 2 Cl 2 ].2H 2 O 1.447 × 10 − 5 7.670 × 10 − 3 4.28 3 Octahedral Paramagnetic L = C 7 H 11 N 4 S Table 4 Solubility behavior of the thiosemicarbazone ligand and its metal(II) complexes in common solvents Compound Water Methanol Ethanol D.ether Acetone DMSO DMF Hexane P.ether Thiosemicarbazone IS SS SS IS S S S IS IS [Mn(L) 2 Cl 2 ].2H 2 O IS SS SS IS SS S S IS IS [Fe(L) 2 Cl 2 ].3H 2 O IS SS SS IS SS S S IS IS [Co(L) 2 Cl 2 ].2H 2 O IS SS SS IS SS S S IS IS L = C 7 H 11 N 4 S Table 5 Elemental Analysis data of the thiosemicarbazone and its metal complexes Compounds %C Elemental Analyses Calculated(observed) %H %N %S %M Thiosemicarbazone 45.9(44.91) 6.01(5.85) 30.60(30.10) 17.49(17.23) - [Mn(L) 2 Cl 2 ].2H 2 O 31.15(31.20) 4.60(3.08) 19.92(19.57) 11.38(11.08) 10.44(8.73) [Fe(L) 2 Cl 2 ].3H 2 O 32.63(31.45) 4.69(3.95) 16.31(17.32) 13.31(12.45) 10.84(10.23) [Co(L) 2 Cl 2 ].2H 2 O 31.70(30.75) 4.56(4.37) 19.17(19.81) 10.97(11.51) 11.11(10.15) L = C 7 H 11 N 4 S Table 6 Infrared Spectral data of Thiosemicarbazone and its Metal (II) Complexes Compounds ν(-OH) cm − 1 ν(C = N) cm − 1 ν(C = S) cm − 1 ν(C-S) cm − 1 ν(M-S) cm − 1 ν(M-N) cm − 1 ν(M-Cl) cm − 1 Thiosemicarbazone - 1618 1296 734 - - - [Mn(L) 2 Cl 2 ].2H 2 O 3443 1607 1236 752 532 414 360 [Fe(L) 2 Cl 2 ].3H 2 O 3340 1622 1227 747 563 430 336 [Co(L) 2 Cl 2 ].2H 2 O 3476 1592 1268 747 603 469 300 L = C 7 H 11 N 4 S Table 7 Electronic spectral data of the thiosemicarbazone ligand and its metal(II) complexes in DMSO. Compounds π→π*(nm) C = S Absorbance π→π* (nm) C = N Absorbance n→π (nm) C = S Absorbance n→π (nm) C = N Absorbance Thiosemicarbazone 242 3.9 266 3.8 327 10 347 10 [Mn(L) 2 Cl 2 ].2H 2 O 243 1.3 262 3.6 333 6.6 356 5.4 [Fe(L) 2 Cl 2 ].3H 2 O 249 9.2 286 8.5 359 7.8 366 8.4 [Co(L) 2 Cl 2 ].2H 2 O 235 0.4 262 2.3 338 1.2 380 1.0 L = C 7 H 11 N 4 S Discussion Physical Properties and Composition The thiosemicarbazone ligand (L) was successfully synthesized by condensation of 4-methyl-3- thiosemicarbazide with pyrrole-2-carboxaldehyde in a 1:1 molar ratio. The ligand was obtained as a light-brown solid with a melting point of 160°C and a percentage yield of 66.6% (Table 1 ), indicating satisfactory product formation and reasonable purity. The sharp melting point further suggests the formation of a well-defined molecular species. Complexation of the ligand with Mn(II), Fe(II), and Co(II) ions in ethanolic medium using a 2:1 ligand-to-metal ratio resulted in distinct colour changes from light brown to cream, coffee brown, and dark brown, respectively (Table 1 ). These colour variations are characteristic of electronic d-d transitions and ligand field effects associated with the respective metal ions, providing preliminary evidence for successful coordination [ 16 ] and [ 17 ]. The observed colour intensification upon complex formation is consistent with metal-ligand charge transfer (MLCT) interactions commonly reported for thiosemicarbazone metal complexes [ 18 ]. The metal (II) complexes did not exhibit definite melting points but decomposed at elevated temperatures ranging from 207–228°C (Table 1 ). These decomposition temperatures are significantly higher than the melting point of the free ligand, indicating enhanced thermal stability upon coordination [ 19 ], [ 20 ]. This increase in thermal stability is attributed to chelation, which strengthens metal-nitrogen and metal-sulfur bonds, reduces molecular flexibility, and increases rigidity of the coordination framework. Among the complexes, the Co(II) complex displayed the highest decomposition temperature (228°C), suggesting comparatively stronger metal-ligand interactions, while the Mn(II) complex decomposed at the lowest temperature (207°C). The percentage yields of the complexes ranged from 62.1–80.5%, with the Co(II) complex showing the highest yield (80.5%). This suggests favorable coordination conditions and efficient metal-ligand interaction in the Co(II) system. The slightly lower yields observed for the Mn(II) and Fe(II) complexes may be attributed to differences in ionic radius, coordination tendencies, and hydration behavior of the metal ions. Solubility and Molar Conductance Solubility studies (Table 4 ) revealed that the ligand and all metal complexes are soluble in polar aprotic solvents such as DMSO and DMF, slightly soluble in methanol, ethanol, and acetone, and insoluble in water, diethyl ether, hexane, and petroleum ether. The good solubility in DMSO and DMF reflects the polar nature of the ligand framework, while insolubility in water indicates non-electrolytic behavior and hydrophobic character of the complexes, which is typical for neutral transition metal chelates [ 21 ]. Molar conductance measurements carried out in DMSO at a concentration of 1 × 10⁻³ mol dm⁻³ gave values in the range of 13.5–19.5 Ω⁻¹ cm² mol⁻¹ (Table 2 ). According to Geary’s classification, these low values are indicative of non-electrolytic complexes. This confirms that the chloride ions are coordinated within the inner coordination sphere rather than existing as free counter ions in solution. The use of DMSO, a polar aprotic solvent with high dielectric constant, further stabilizes neutral species and limits ionic dissociation, leading to reduced molar conductance values [ 22 ] [ 23 ] [ 24 ]. Magnetic Properties and Geometry The magnetic susceptibility data (Table 3 ) provide strong evidence for the proposed octahedral geometries of the complexes. The Mn(II) complex exhibited an effective magnetic moment of 5.97 BM, consistent with a high-spin d⁵ configuration containing five unpaired electrons [ 25 ]. The Fe(II) complex showed a magnetic moment of 5.09 BM, corresponding to a high-spin d⁶ octahedral environment with four unpaired electrons. The Co(II) complex displayed a magnetic moment of 4.28 BM, characteristic of high-spin octahedral d⁷ systems with three unpaired electrons [ 23 ]. These values fall within the expected ranges for octahedral Mn(II), Fe(II), and Co(II) complexes and confirm their paramagnetic nature. Elemental and Metal Content Analysis Elemental (CHNS) analysis results (Table 5 ) showed good agreement between calculated and experimentally observed values for the ligand and its complexes, confirming the proposed stoichiometry and purity of the synthesized compounds [ 27 ] Minor deviations between calculated and observed values fall within acceptable analytical limits and are commonly associated with experimental conditions and hydration effects. The metal content values further support a 1:2 metal-to-ligand ratio in all complexes. Atomic absorption spectroscopy (AAS) was used to determine the metal content of the complexes as presented in Table 5 . The observed values in the range of 8.73–10.23% in the complexes showed deviation from theoretical percentage 10.44–11.11%. These values were closer to the value 6.64–7.86% reported by [ 28 ].The result confirmed a 1:2 metal-ligand stoichiometry thus supporting the proposed [ML 2 ] formulation and also validate the composition as well as the purity of the synthesized complexes. Infrared Spectral Analysis FTIR spectral data (Table 6 ), Figs. 3 , 4 , 5 , 6 provided decisive evidence for the coordination mode of the ligand. The free ligand exhibited a strong azomethine ν(C = N) band at 1618 cm⁻¹, confirming successful Schiff base formation. Upon coordination, this band shifted to 1607–1622 cm⁻¹ in the complexes, indicating involvement of the azomethine nitrogen in bonding with the metal ions. The ν(C = S) band of the ligand at 1296 cm⁻¹ shifted to lower frequencies (1227–1268 cm⁻¹) in the complexes, while the ν(C-S) band also showed noticeable shifts, confirming coordination through the thione sulfur atom. The absence of an S-H band in the ligand spectrum indicates that the ligand exists predominantly in the thione form. The appearance of new bands in the regions 532–603 cm⁻¹ and 414–469 cm⁻¹ in the spectra of the complexes were assigned to ν(M-S) and ν(M-N) vibrations, respectively, further confirming bidentate coordination through sulfur and nitrogen atoms [ 29 ]; [ 30 ]. Bands observed in the range 300–360 cm⁻¹ were attributed to ν(M-Cl) stretching vibrations, supporting the coordination of chloride ions. Broad absorption bands between 3340–3476 cm⁻¹ were assigned to ν(O-H) stretching of coordinated water molecules, consistent with the hydrated nature of the complexes indicated in their empirical formulas [ 31 ]. Electronic Spectral Studies The electronic spectra (Table 6 ) of the thiosemicarbazone ligand and its Mn(II), Fe(II), and Co(II) complexes recorded in DMSO exhibit characteristic π→π* and n→π* transitions associated with the C = N and C = S chromophores. The free ligand shows intense bands at 242 and 266 nm attributed to π→π* transitions, and bands at 327 and 347 nm assigned to n→π* transitions. Upon coordination, these bands undergo slight bathochromic shifts accompanied by changes in absorbance intensity, indicating involvement of the azomethine nitrogen and thione sulfur atoms in metal–ligand bonding. The observed spectral shifts reflect modification of the ligand electronic environment due to coordination. The absence of well-resolved d–d transitions is attributed to their low intensity and overlap with ligand-centered transitions. Overall, the electronic spectral data support complex formation and are consistent with the proposed octahedral geometry of the metal(II) complexes. In octahedral complexes, d–d transitions are formally Laporte forbidden and therefore intrinsically low in intensity; such transitions become weakly allowed through vibronic coupling and other symmetry-breaking mechanisms. These low-intensity d–d bands are often masked by more intense ligand-centered π→π* and n→π* absorptions in the UV–visible region, resulting in poorly resolved or overlapping spectral features in the electronic spectra of the complexes. Collectively, the physicochemical, magnetic, spectroscopic, and analytical results conclusively demonstrate that the thiosemicarbazone ligand (L) coordinates in a bidentate manner through azomethine nitrogen and thione sulfur atoms. The remaining coordination sites are occupied by chloride ions and water molecules, resulting in stable six-coordinate octahedral Mn(II), Fe(II), and Co(II) complexes. Table 8 Antibacterial Activity (Zone of Inhibition, mm) of the Schiff base Ligand (L) and its Mn(II), Fe(II), and Co(II) Complexes Compound Concentration (µg/mL) Gram-positive Bacteria (mm) Gram-negative Bacteria (mm) Staphylococcus aureus Escherichia coli Salmonella typhi Thiosemicarbazone 2000 13 16 13 1000 11 13 10 500 09 11 8 250 06 09 07 [Mn(L) 2 Cl 2 ].2H 2 O 2000 20 19 17 1000 17 16 14 500 15 14 11 250 12 12 10 [Fe(L) 2 Cl 2 ].3H 2 O 2000 22 17 17 1000 19 15 16 500 17 12 14 250 15 11 12 [Co(L) 2 Cl 2 ].2H 2 O 2000 21 18 15 1000 19 14 13 500 16 13 10 250 13 10 09 Ciprofloxacin 26 25 19 L = C 7 H 11 N 4 S Table 9 Antifungal Activity (Zone of Inhibition, mm) of the Schiff base Ligand (L) and its Mn(II), Fe(II), and Co(II) Complexes Compound Concentration (µg/mL) Fungi Candida Albicans Tinea pedis Aspergillus flavus Thiosemicarbazone 2000 14 16 13 1000 11 13 10 500 09 11 08 250 07 09 07 [Mn(L) 2 Cl 2 ].2H 2 O 2000 21 22 14 1000 20 17 10 500 18 13 11 250 15 10 09 [Fe(L) 2 Cl 2 ].3H 2 O 2000 21 20 15 1000 15 18 13 500 13 16 12 250 11 14 10 [Co(L) 2 Cl 2 ].2H 2 O 2000 21 23 15 1000 17 19 13 500 15 15 12 250 11 13 10 Ketoconazole 26 25 19 L = C 7 H 11 N 4 S Antimicrobial activity The antimicrobial evaluation clearly shows that coordination of the thiosemicarbazone ligand with Mn(II), Fe(II), and Co(II) ions leads to a consistent improvement in both antibacterial and antifungal activities. In all cases, the metal complexes produced larger zones of inhibition than the free ligand, highlighting the central role of metal coordination in enhancing biological performance. This improvement is reasonably attributed to chelation, which reduces the polarity of the ligand and increases overall lipophilicity, thereby facilitating penetration across microbial cell membranes [ 32 ] Bacterial susceptibility was strongly influenced by cell wall structure. The Gram-positive Staphylococcus aureus exhibited greater sensitivity than the Gram-negative strains, consistent with the absence of an outer lipopolysaccharide barrier. Among the complexes, the Fe(II) and Co(II) derivatives showed the highest activity against S. aureus , suggesting that their electronic configurations and redox characteristics favor effective intracellular disruption. In contrast, Escherichia coli and Salmonella typhi displayed lower susceptibility, reflecting the additional permeability barriers and efflux mechanisms typical of Gram-negative bacteria. Notably, the Mn(II) complex demonstrated comparatively enhanced activity against E. coli , indicating that the nature of the metal center can influence selectivity, possibly through differences in uptake pathways or interactions with bacterial transport systems. The antifungal results further support the beneficial impact of metal coordination. All metal complexes showed improved activity against Candida albicans , Tinea pedis , and Aspergillus flavus compared with the free ligand, although ketoconazole remained the most active reference compound. The Co(II) complex exhibited the strongest antifungal effect, particularly against T. pedis , where its activity closely approached that of the standard drug. Against the more resistant A. flavus , moderate but meaningful enhancement was observed upon complexation, demonstrating that metal coordination can broaden antifungal activity even against less susceptible fungal species [ 33 ] Across all microbial assays, larger inhibition zones were consistently observed at lower test concentrations. This trend is likely associated with improved diffusion and reduced aggregation of the complexes in the agar medium, emphasizing that physicochemical behavior plays an important role in determining apparent biological activity. Overall, the antimicrobial effectiveness followed the trend Fe(II) ≈ Co(II) > Mn(II) > free ligand, underscoring the importance of metal identity in modulating potency and spectrum of activity[ 11 ] Proposed mechanism of antimicrobial action The enhanced antimicrobial activity of the metal complexes appears to arise from a combination of physicochemical and biochemical effects. Chelation increases lipophilicity and membrane permeability, allowing more efficient intracellular access. Once inside the cell, the metal centers may interfere with essential biological processes through enzyme inhibition, displacement of native metal ions from proteins, and redox-mediated generation of reactive oxygen species. The resulting oxidative damage to membranes, proteins, and nucleic acids likely contributes to the superior antibacterial and antifungal activities observed for the metal complexes relative to the uncoordinated ligand [ 34 ] [ 35 ]. CONCLUSION A novel pyrrole-based thiosemicarbazone Schiff base ligand was successfully synthesized and coordinated with Mn(II), Fe(II), and Co(II) ions to yield stable transition metal complexes. Detailed physicochemical and spectroscopic analyses confirmed that the ligand coordinates in a bidentate manner through the azomethine nitrogen and thione sulfur atoms, resulting in six-coordinate octahedral geometries for all the complexes. Magnetic susceptibility measurements indicated high-spin configurations, fully consistent with the proposed structures, while the low molar conductance values verified the non-electrolytic nature of the complexes. Metal coordination significantly improved the thermal stability of the ligand and induced noticeable changes in its electronic properties, as reflected by higher decomposition temperatures and diagnostic spectral shifts. The proposed compositions and purity of the synthesized compounds were further supported by elemental analysis and atomic absorption spectroscopy. Biological screening demonstrated that the metal complexes exhibit markedly enhanced antibacterial and antifungal activities compared to the free ligand, with the Fe(II) and Co(II) complexes showing the strongest inhibitory effects. This improvement in antimicrobial performance is attributed to chelation, which increases lipophilicity and facilitates penetration through microbial cell membranes, along with potential metal-mediated interactions that disrupt essential intracellular processes. The observed variation in activity among the complexes highlights the critical role of the metal ion in modulating biological efficacy. Overall, the findings confirm that pyrrole-based thiosemicarbazone ligands are effective chelating systems for the generation of biologically active transition metal complexes. This work provides meaningful insights into structure–property–activity relationships and supports the continued development of thiosemicarbazone metal complexes as promising candidates for antimicrobial applications. Declarations Ethics Approval and Consent to Participate This study did not involve human participants or animals. Ethical approval and consent to participate were therefore not required. Consent to Publish Not applicable. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Author Contribution The author conceptualize the study, carried out the synthesis and Characterization of the ligand and metal complexes, performed the biological experiments, analyzed and interpreted the data and wrote the original draft of the manuscript. The author also reviewed and approved the final version of the manuscript. 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Antibiotics. 2022;11(10):1392. Balouiri M, Sadiki M, Ibnsouda SK. Methods for in vitro evaluating antimicrobial activity: A review. J Pharm Anal. 2016;6(2):71–9. Aly AA, Mohamed AA, El-Sayed MA. Metal–ligand chelation and its role in antimicrobial activity. Appl Organomet Chem. 2023;37(5):e7064. Qamar HMG, Bashir T, Ibrahim U, et al. Antibacterial activity of transition metal thiosemicarbazone complexes. Futuristic Biotechnol. 2024;4(3):62–7. Schemes Scheme 1 is available in the Supplementary Files section Additional Declarations No competing interests reported. Supplementary Files image1.png Scheme 1: Synthesis of Thiosemicarbazone and its Metal (II) Complexes Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 21 Jan, 2026 Editor assigned by journal 06 Jan, 2026 Submission checks completed at journal 06 Jan, 2026 First submitted to journal 30 Dec, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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4","display":"","copyAsset":false,"role":"figure","size":40153,"visible":true,"origin":"","legend":"\u003cp\u003eBar Chart showing the Antifungal activity of the ligand and its metal (II) complexes against \u003cem\u003eCandida albican.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-8484646/v1/077b9d5500f53c5093a7e94a.png"},{"id":99795994,"identity":"37433946-4be8-4fa1-81da-5ba5efc203b1","added_by":"auto","created_at":"2026-01-08 13:40:12","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":40342,"visible":true,"origin":"","legend":"\u003cp\u003eBar Chart showing the Antifungal activity of the ligand and its metal (II) complexes against \u003cem\u003eTinea capitis\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-8484646/v1/7d3db0472b2023be0ae62fc5.png"},{"id":100356504,"identity":"2837c5d3-ced4-4a75-aaef-d0e0da14ec63","added_by":"auto","created_at":"2026-01-16 07:13:48","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":41165,"visible":true,"origin":"","legend":"\u003cp\u003eBar Chart showing the Antifungal activity of the ligand and its metal (II) complexes against \u003cem\u003eAspergillus flavus\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-8484646/v1/f7e31eac1372ddd1cef33532.png"},{"id":99796517,"identity":"787dcf23-8c62-47a1-ab0e-39ee6e829ed0","added_by":"auto","created_at":"2026-01-08 13:42:37","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":76629,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR Spectrum of Thiosemicarbazone\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-8484646/v1/ad7bdfc726cd6cfe8cc7a6bf.png"},{"id":99796831,"identity":"183f8e94-02a1-4408-9b0c-dd197a98cbb7","added_by":"auto","created_at":"2026-01-08 13:43:46","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":68920,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR Spectrum of Thiosemicarbazone Mn(II) complex\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-8484646/v1/be7eb89b2fa7e6ea39422903.png"},{"id":99795992,"identity":"6b81e5f3-4e8d-44f2-b8a7-97d255e019ec","added_by":"auto","created_at":"2026-01-08 13:40:12","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":67392,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR \u0026nbsp;\u0026nbsp;Spectrum of Thiosemicarbazone Fe(II) complex\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-8484646/v1/dbaa8357798e6a0762e0f44a.png"},{"id":99795736,"identity":"f0937b2d-6531-43f2-8cb9-ced73adc28cd","added_by":"auto","created_at":"2026-01-08 13:39:35","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":72180,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR \u0026nbsp;\u0026nbsp;Spectrum of Thiosemicarbazone Co(II) complex\u003c/p\u003e","description":"","filename":"image11.png","url":"https://assets-eu.researchsquare.com/files/rs-8484646/v1/72fc6619b1b70545e21bfbd4.png"},{"id":100406528,"identity":"4bb9c18e-3a5c-46ed-a4af-0fad61c7541b","added_by":"auto","created_at":"2026-01-16 13:02:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1751813,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8484646/v1/1f32172c-be7b-4500-8683-f6c922ff017a.pdf"},{"id":99703950,"identity":"bc93a3d5-a21c-4285-804b-cdb195087ca2","added_by":"auto","created_at":"2026-01-07 12:16:42","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":24076,"visible":true,"origin":"","legend":"\u003cp\u003eScheme 1: Synthesis of Thiosemicarbazone and its Metal (II) Complexes\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-8484646/v1/77b165ecb95e4e34bb11fe11.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"Synthesis, Characterization, and Antimicrobial Evaluation of Mn(II), Fe(II), and Co(II) Complexes of a Pyrrole-Based Thiosemicarbazone Schiff Base","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eHeterocyclic compounds are a central class of organic molecules in which one or more ring carbon atoms are replaced by heteroatoms such as nitrogen, oxygen, sulfur, or phosphorus. Their unique electronic properties, structural diversity, and functional adaptability underpin their widespread importance in synthetic, medicinal, and coordination chemistry [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] Heterocycles form the core frameworks of numerous natural products and pharmaceutical agents, and recent drug-development analyses show that most newly approved therapeutics incorporate at least one heterocyclic moiety, underscoring their continued relevance in molecular design\u003c/p\u003e \u003cp\u003eNitrogen- and sulfur-containing heterocycles are particularly significant in coordination chemistry due to their strong donor ability and directional bonding with transition metals. Coordination through these heteroatoms produces complexes with well-defined geometries, tunable electronic structures, and diverse magnetic, redox, and biological properties [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] Among such ligands, Schiff bases derived from heteroaromatic aldehydes and amines are especially attractive because of their synthetic accessibility, structural flexibility, and multidentate coordination behavior [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]).\u003c/p\u003e \u003cp\u003eThiosemicarbazones constitute an important subclass of Schiff base ligands characterized by the presence of azomethine nitrogen and thione sulfur donor sites within the same framework. They are typically synthesized via condensation of thiosemicarbazide or its derivatives with aldehydes or ketones, generating a C\u0026thinsp;=\u0026thinsp;N linkage adjacent to a C\u0026thinsp;=\u0026thinsp;S group under mild reaction conditions [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] This donor set enables strong chelation, often leading to thermally stable complexes with enhanced biological and physicochemical properties. Following early reports of antibacterial activity, thiosemicarbazones gained prominence after the discovery of their antitubercular and anticancer potential, stimulating extensive research into their metal complexes [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eCoordination compounds, formed through coordinate covalent bonding between metal ions and ligands, are fundamental to inorganic chemistry. Their structures and properties such as geometry, magnetism, color, and reactivity are governed by the electronic configuration of the metal center and the nature of the coordinating ligands [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] Transition metals, owing to their partially filled d-orbitals and variable oxidation states, play crucial roles in biological redox processes and modern catalysis, and have become indispensable in medicinal inorganic chemistry [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eThiosemicarbazone ligands exhibit versatile coordination modes, acting as mono-, bi-, or polydentate donors depending on substitution and reaction conditions. Their ability to form stable chelate rings enhances the thermal stability and biological activity of their metal complexes, which frequently display superior antimicrobial, anticancer, antiviral, and antioxidant properties compared to free ligands [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]; [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] In addition to biomedical relevance, these complexes find applications in analytical chemistry, sensing, and materials science, highlighting thiosemicarbazones as key ligands at the interface of heterocyclic chemistry, coordination chemistry, and functional materials research. This study aims to synthesize a new heterocyclic thiosemicarbazone Schiff base and its Mn(II), Fe(II), and Co(II) complexes, and to elucidate their coordination modes, structural characteristics, physicochemical properties, and antimicrobial potential in relation to metal chelation.\u003c/p\u003e"},{"header":"EXPERIMENTAL","content":"\n\u003ch3\u003eMaterials and Methods\u003c/h3\u003e\n\u003cp\u003eAll chemicals and solvents were of analytical reagent grade and used as received without further purification. 4-methyl-3-thiosemicarbazide (T33405) and pyrrole-2-carboxaldehyde (P73404) were purchased from Sigma-Aldrich. Ethanol, methanol, diethyl ether, and dimethyl sulfoxide (DMSO) were of analytical grade. All glassware was thoroughly cleaned, rinsed with distilled water, and oven-dried at 110\u0026deg;C prior to use. Weighing was carried out using a Mettler Toledo analytical balance (Model AB54). Melting and decomposition temperatures were determined using a Gallenkamp SMP10 melting point apparatus. Elemental analyses were recorded using Series II CHNS/O 2400 Perkin Elmer.\u003c/p\u003e \u003cp\u003e Scheme 1: Synthesis of Thiosemicarbazone and its Metal (II) Complexes\u003c/p\u003e\n\u003ch3\u003eSynthesis of the Thiosemicarbazone ligand\u003c/h3\u003e\n\u003cp\u003eAn ethanolic solution (20 mL) of 4-methyl-3-thiosemicarbazide (1.05 g, 10 mmol) was mixed with an ethanolic solution (20 mL) of pyrrole-2-carboxaldehyde (0.95 g, 10 mmol), followed by the addition of 2\u0026ndash;3 drops of glacial acetic acid as catalyst. The reaction mixture was refluxed at approximately 80\u0026deg;C for 4 h and then allowed to cool to room temperature. The resulting precipitate was filtered, washed with diethyl ether, recrystallized from methanol, and dried in a desiccator over anhydrous calcium chloride [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e\n\u003ch3\u003eSynthesis of Metal (II) Complexes\u003c/h3\u003e\n\u003cp\u003eThe metal complexes were prepared by adding a hot ethanolic solution (20 mL) of the ligand (0.73 g, 0.004 mol) dropwise to a hot ethanolic solution (20 mL) of the corresponding metal(II) chloride salt (0.002 mol) under constant stirring. The reaction mixture was refluxed at approximately 80\u0026deg;C for 5 h. After cooling to room temperature, the resulting complexes were filtered, washed with diethyl ether, recrystallized from methanol, and dried in a desiccator over anhydrous calcium chloride [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]..\u003c/p\u003e\n\u003ch3\u003eMolar Conductivity Measurements\u003c/h3\u003e\n\u003cp\u003eMolar conductance measurements were carried out at room temperature using a Jenway conductivity meter (Model 4010). Solutions of the metal complexes were prepared in DMSO, and the instrument was calibrated using standard potassium chloride solutions.\u003c/p\u003e\n\u003ch3\u003eMagnetic Susceptibility Measurements\u003c/h3\u003e\n\u003cp\u003eMagnetic susceptibility measurements were performed at room temperature using a Sherwood magnetic susceptibility balance. The effective magnetic moments were calculated to determine the electronic configuration and geometry of the metal centers.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eInfrared Spectral Analysis\u003c/h2\u003e \u003cp\u003eFourier transform infrared (FT-IR) spectra of the ligand and its metal(II) complexes were recorded in the range 4000\u0026ndash;400 cm⁻\u0026sup1; using a Cary 630 FT-IR spectrometer (Agilent Technologies) to confirm functional group formation and metal\u0026ndash;ligand coordination.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eUV–Visible Spectral Analysis\u003c/h3\u003e\n\u003cp\u003eElectronic spectra were recorded at room temperature in the range 200\u0026ndash;600 nm using a PerkinElmer Lambda 35 UV\u0026ndash;Visible spectrophotometer to study ligand-centered, d\u0026ndash;d, and charge-transfer transitions.\u003c/p\u003e\n\u003ch3\u003eDetermination of Metal Content\u003c/h3\u003e\n\u003cp\u003eApproximately 0.20 g of each metal complex was digested with concentrated HNO₃ (5 mL) and HCl (15 mL) and heated to near dryness. The residue was filtered, diluted to 100 mL with deionized water, and analyzed for metal content using atomic absorption spectroscopy (AAS) following reported procedures.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eAntimicrobial Assay\u003c/h2\u003e \u003cp\u003eIn vitro antimicrobial assays are routinely employed to evaluate the inhibitory potential of chemical compounds against pathogenic microorganisms. Such assays are widely used in clinical diagnostics, pharmaceutical development and research to identify effective antimicrobial agents and monitor resistance patterns. In the present study, the antimicrobial activity of the synthesized thiosemicarbazone ligand and its metal(II) complexes was evaluated using the agar well diffusion technique, which is a reliable and commonly adopted screening method.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of Stock Solution and Working Concentrations\u003c/h2\u003e \u003cp\u003eStock solutions of the thiosemicarbazone ligand and its metal(II) complexes were prepared at a concentration of 2000 \u0026micro;g/mL by dissolving 2 mg of each compound in 1 mL of dimethyl sulfoxide (DMSO) in sterile bijou bottles. Working concentrations of 125, 250, 500 and 1000 \u0026micro;g/mL were obtained from the stock solutions by serial dilution, following the procedure reported by [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] with slight modifications. DMSO was used as the solvent control throughout the study.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of Culture Media and Test Organisms\u003c/h2\u003e \u003cp\u003eThe antimicrobial activity was evaluated against selected pathogenic microorganisms, including \u003cem\u003eStaphylococcus aureus\u003c/em\u003e, \u003cem\u003eEscherichia coli\u003c/em\u003e, and \u003cem\u003eSalmonella typhi\u003c/em\u003e for antibacterial screening, and \u003cem\u003eCandida albican\u003c/em\u003e, \u003cem\u003eTinea pedis\u003c/em\u003e and \u003cem\u003eAspergillus flavus\u003c/em\u003e for antifungal screening. The bacterial and fungal isolates were obtained from Aminu Kano Teaching Hospital and identified at the Department of Microbiology, Bayero University, Kano.\u003c/p\u003e \u003cp\u003eMueller\u0026ndash;Hinton agar (MHA) was used for antibacterial studies, while Potato Dextrose Agar (PDA) was employed for antifungal studies. The media were prepared according to the manufacturer\u0026rsquo;s instructions by dissolving 48 g of MHA and 39 g of PDA separately in 1000 mL of distilled water, followed by sterilization in an autoclave at 121\u0026deg;C for 15 minutes. The molten media were poured into sterile Petri dishes and allowed to cool to approximately 45\u0026deg;C. Wells of 6 mm diameter were made at equidistant positions using a sterile cork borer.\u003c/p\u003e \u003cp\u003eThe test organisms were standardized using 0.5 McFarland standard, as described by Usman and [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], to ensure uniform microbial density.\u003c/p\u003e \u003cp\u003e \u003cb\u003eIn vitro\u003c/b\u003e \u003cb\u003eAntibacterial Activity\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe antibacterial activity of the thiosemicarbazone ligand and its metal(II) complexes was evaluated against \u003cem\u003eStaphylococcus aureus\u003c/em\u003e, \u003cem\u003eEscherichia coli\u003c/em\u003e, and \u003cem\u003eSalmonella typhi\u003c/em\u003e using the agar well diffusion method. Fresh bacterial suspensions were uniformly swabbed onto the surface of solidified Mueller\u0026ndash;Hinton agar plates. Aliquots of the prepared test solutions at concentrations of 125, 250, 500 and 1000 \u0026micro;g/mL were introduced into the wells.\u003c/p\u003e \u003cp\u003eThe plates were incubated at 37\u0026deg;C for 24 hours, after which the zones of inhibition were measured in millimeters using a vernier caliper. Ciprofloxacin was used as the positive control, while DMSO served as the negative control. Antibacterial activity was assessed by comparing the inhibition zones of the test compounds with those of the standard drug.\u003c/p\u003e \u003cp\u003e \u003cb\u003eIn vitro\u003c/b\u003e \u003cb\u003eAntifungal Activity\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe antifungal activity of the ligand and its metal(II) complexes was investigated against \u003cem\u003eCandida albican\u003c/em\u003e, \u003cem\u003eTinea pedis\u003c/em\u003e and \u003cem\u003eAspergillus flavus\u003c/em\u003e using the agar well diffusion technique. Standardized fungal suspensions were swabbed onto the surface of solidified Potato Dextrose Agar plates. Test solutions of the compounds at concentrations of 125, 250, 500 and 1000 \u0026micro;g/mL were dispensed into the wells. The plates were incubated at 37\u0026deg;C for 48 hours, after which zones of complete inhibition were measured in millimeters. Ketoconazole was employed as the positive control, while DMSO served as the negative control. Antifungal activity was determined by comparing the inhibition zones produced by the test compounds with those of the standard antifungal agent.\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS AND DISCUSSION","content":"\u003cp\u003eThe tables below present the results obtained from the physicochemical analysis, spectral characterization, and \u003cem\u003ein-vitro\u003c/em\u003e antimicrobial evaluation of the thiosemicarbazone and its complexes.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePhysical properties and percentage yields of the thiosemicarbazone ligand and its metal (II) complexess\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCompounds\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eColor\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMelting point (⁰C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDecomposition Temperature (⁰C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePercentage Yield (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThiosemicarbazone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLight brown\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e160\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e66.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[Mn(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCream\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e207\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e64.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[Fe(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCoffee Brown\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e220\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e62.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[Co(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDark brown\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e228\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e80.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eL\u0026thinsp;=\u0026thinsp;C\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e11\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMolar conductance values of Mn(II), Fe(II), and Co(II) complexes in DMSO (1 \u0026times; 10⁻\u0026sup3; mol dm⁻\u0026sup3;).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComplex\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eConcentration Moldm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSpecific Conductance\u003c/p\u003e \u003cp\u003eOhm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003ecm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMolar Conductance\u003c/p\u003e \u003cp\u003eOhm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003ecm\u003csup\u003e2\u003c/sup\u003emol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[Mn(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.0 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13.50 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[Fe(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.0 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.4 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[Co(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.0 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.5 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eL\u0026thinsp;=\u0026thinsp;C\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e11\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMagnetic susceptibility data and proposed geometries of the thiosemicarbazone metal(II) complexes.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eCompound\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eXg(erg.c\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003eg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eXm(erg.c\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003emol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026micro;\u003csub\u003eeff\u003c/sub\u003e(BM)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eGeometry\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eProperty\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e[Mn(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e2.834 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.495 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eOctahedral\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eParamagnetic\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e[Fe(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e1.97 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.086 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eOctahedral\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eParamagnetic\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e[Co(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e1.447 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.670 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eOctahedral\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eParamagnetic\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003eL\u0026thinsp;=\u0026thinsp;C\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e11\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003eS\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSolubility behavior of the thiosemicarbazone ligand and its metal(II) complexes in common solvents\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"19\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c15\" colnum=\"15\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c16\" colnum=\"16\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c17\" colnum=\"17\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c18\" colnum=\"18\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c19\" colnum=\"19\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCompound\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eWater\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eMethanol\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eEthanol\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003eD.ether\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e \u003cp\u003eAcetone\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e \u003cp\u003eDMSO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e \u003cp\u003eDMF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e \u003cp\u003eHexane\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c19\" namest=\"c18\"\u003e \u003cp\u003eP.ether\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThiosemicarbazone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c18\" namest=\"c17\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c19\" namest=\"c19\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[Mn(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c18\" namest=\"c17\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c19\" namest=\"c19\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[Fe(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c18\" namest=\"c17\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c19\" namest=\"c19\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[Co(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c18\" namest=\"c17\"\u003e \u003cp\u003eIS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c19\" namest=\"c19\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eL\u0026thinsp;=\u0026thinsp;C\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e11\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"18\" nameend=\"c19\" namest=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eElemental Analysis data of the thiosemicarbazone and its metal complexes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCompounds\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e%C\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eElemental Analyses\u003c/p\u003e \u003cp\u003eCalculated(observed) %H\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e%N\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e%S\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e%M\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThiosemicarbazone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e45.9(44.91)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.01(5.85)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e30.60(30.10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e17.49(17.23)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[Mn(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31.15(31.20)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.60(3.08)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e19.92(19.57)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e11.38(11.08)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e10.44(8.73)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[Fe(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e32.63(31.45)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.69(3.95)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e16.31(17.32)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e13.31(12.45)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e10.84(10.23)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e[Co(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31.70(30.75)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.56(4.37)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e19.17(19.81)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e10.97(11.51)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e11.11(10.15)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eL\u0026thinsp;=\u0026thinsp;C\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e11\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003eS\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003e\u003cb\u003eInfrared Spectral data of Thiosemicarbazone and its Metal (II) Complexes\u003c/b\u003e\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eCompounds\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eν(-OH) cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eν(C\u0026thinsp;=\u0026thinsp;N) cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eν(C\u0026thinsp;=\u0026thinsp;S) cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eν(C-S) cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eν(M-S) cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eν(M-N) cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eν(M-Cl) cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eThiosemicarbazone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1618\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1296\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e734\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e[Mn(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3443\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1607\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1236\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e752\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e532\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e414\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e360\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e[Fe(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3340\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1622\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1227\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e747\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e563\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e430\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e336\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e[Co(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3476\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1592\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1268\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e747\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e603\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e469\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eL\u0026thinsp;=\u0026thinsp;C\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e11\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"8\" nameend=\"c9\" namest=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab7\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 7\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eElectronic spectral data of the thiosemicarbazone ligand and its metal(II) complexes in DMSO.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"11\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eCompounds\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eπ\u0026rarr;π*(nm) C\u0026thinsp;=\u0026thinsp;S\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAbsorbance\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eπ\u0026rarr;π* (nm) C\u0026thinsp;=\u0026thinsp;N\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAbsorbance\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003en\u0026rarr;π (nm) C\u0026thinsp;=\u0026thinsp;S\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eAbsorbance\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003en\u0026rarr;π (nm) C\u0026thinsp;=\u0026thinsp;N\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eAbsorbance\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eThiosemicarbazone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e242\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e266\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e327\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e347\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e[Mn(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e243\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e262\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e333\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e6.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e356\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e5.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e[Fe(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e249\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e9.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e286\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e8.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e359\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e7.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e366\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e8.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e[Co(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e235\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e262\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e338\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e380\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"11\"\u003eL\u0026thinsp;=\u0026thinsp;C\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e11\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003eS\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/br\u003e\u003c/div\u003e\n\u003ch3\u003eDiscussion\u003c/h3\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003ePhysical Properties and Composition\u003c/h2\u003e \u003cp\u003eThe thiosemicarbazone ligand (L) was successfully synthesized by condensation of 4-methyl-3- thiosemicarbazide with pyrrole-2-carboxaldehyde in a 1:1 molar ratio. The ligand was obtained as a light-brown solid with a melting point of 160\u0026deg;C and a percentage yield of 66.6% (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), indicating satisfactory product formation and reasonable purity. The sharp melting point further suggests the formation of a well-defined molecular species.\u003c/p\u003e \u003cp\u003eComplexation of the ligand with Mn(II), Fe(II), and Co(II) ions in ethanolic medium using a 2:1 ligand-to-metal ratio resulted in distinct colour changes from light brown to cream, coffee brown, and dark brown, respectively (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These colour variations are characteristic of electronic d-d transitions and ligand field effects associated with the respective metal ions, providing preliminary evidence for successful coordination [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] and [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The observed colour intensification upon complex formation is consistent with metal-ligand charge transfer (MLCT) interactions commonly reported for thiosemicarbazone metal complexes [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe metal (II) complexes did not exhibit definite melting points but decomposed at elevated temperatures ranging from 207\u0026ndash;228\u0026deg;C (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These decomposition temperatures are significantly higher than the melting point of the free ligand, indicating enhanced thermal stability upon coordination [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. This increase in thermal stability is attributed to chelation, which strengthens metal-nitrogen and metal-sulfur bonds, reduces molecular flexibility, and increases rigidity of the coordination framework. Among the complexes, the Co(II) complex displayed the highest decomposition temperature (228\u0026deg;C), suggesting comparatively stronger metal-ligand interactions, while the Mn(II) complex decomposed at the lowest temperature (207\u0026deg;C).\u003c/p\u003e \u003cp\u003eThe percentage yields of the complexes ranged from 62.1\u0026ndash;80.5%, with the Co(II) complex showing the highest yield (80.5%). This suggests favorable coordination conditions and efficient metal-ligand interaction in the Co(II) system. The slightly lower yields observed for the Mn(II) and Fe(II) complexes may be attributed to differences in ionic radius, coordination tendencies, and hydration behavior of the metal ions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eSolubility and Molar Conductance\u003c/h2\u003e \u003cp\u003eSolubility studies (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) revealed that the ligand and all metal complexes are soluble in polar aprotic solvents such as DMSO and DMF, slightly soluble in methanol, ethanol, and acetone, and insoluble in water, diethyl ether, hexane, and petroleum ether. The good solubility in DMSO and DMF reflects the polar nature of the ligand framework, while insolubility in water indicates non-electrolytic behavior and hydrophobic character of the complexes, which is typical for neutral transition metal chelates [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMolar conductance measurements carried out in DMSO at a concentration of 1 \u0026times; 10⁻\u0026sup3; mol dm⁻\u0026sup3; gave values in the range of 13.5\u0026ndash;19.5 Ω⁻\u0026sup1; cm\u0026sup2; mol⁻\u0026sup1; (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). According to Geary\u0026rsquo;s classification, these low values are indicative of non-electrolytic complexes. This confirms that the chloride ions are coordinated within the inner coordination sphere rather than existing as free counter ions in solution. The use of DMSO, a polar aprotic solvent with high dielectric constant, further stabilizes neutral species and limits ionic dissociation, leading to reduced molar conductance values [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eMagnetic Properties and Geometry\u003c/h2\u003e \u003cp\u003eThe magnetic susceptibility data (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) provide strong evidence for the proposed octahedral geometries of the complexes. The Mn(II) complex exhibited an effective magnetic moment of 5.97 BM, consistent with a high-spin d⁵ configuration containing five unpaired electrons [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The Fe(II) complex showed a magnetic moment of 5.09 BM, corresponding to a high-spin d⁶ octahedral environment with four unpaired electrons. The Co(II) complex displayed a magnetic moment of 4.28 BM, characteristic of high-spin octahedral d⁷ systems with three unpaired electrons [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. These values fall within the expected ranges for octahedral Mn(II), Fe(II), and Co(II) complexes and confirm their paramagnetic nature.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eElemental and Metal Content Analysis\u003c/h2\u003e \u003cp\u003eElemental (CHNS) analysis results (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) showed good agreement between calculated and experimentally observed values for the ligand and its complexes, confirming the proposed stoichiometry and purity of the synthesized compounds [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] Minor deviations between calculated and observed values fall within acceptable analytical limits and are commonly associated with experimental conditions and hydration effects. The metal content values further support a 1:2 metal-to-ligand ratio in all complexes.\u003c/p\u003e \u003cp\u003eAtomic absorption spectroscopy (AAS) was used to determine the metal content of the complexes as presented in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The observed values in the range of 8.73\u0026ndash;10.23% in the complexes showed deviation from theoretical percentage 10.44\u0026ndash;11.11%. These values were closer to the value 6.64\u0026ndash;7.86% reported by [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].The result confirmed a 1:2 metal-ligand stoichiometry thus supporting the proposed [ML\u003csub\u003e2\u003c/sub\u003e] formulation and also validate the composition as well as the purity of the synthesized complexes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003eInfrared Spectral Analysis\u003c/h2\u003e \u003cp\u003eFTIR spectral data (Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e,\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e,\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e,\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e provided decisive evidence for the coordination mode of the ligand. The free ligand exhibited a strong azomethine ν(C\u0026thinsp;=\u0026thinsp;N) band at 1618 cm⁻\u0026sup1;, confirming successful Schiff base formation. Upon coordination, this band shifted to 1607\u0026ndash;1622 cm⁻\u0026sup1; in the complexes, indicating involvement of the azomethine nitrogen in bonding with the metal ions. The ν(C\u0026thinsp;=\u0026thinsp;S) band of the ligand at 1296 cm⁻\u0026sup1; shifted to lower frequencies (1227\u0026ndash;1268 cm⁻\u0026sup1;) in the complexes, while the ν(C-S) band also showed noticeable shifts, confirming coordination through the thione sulfur atom. The absence of an S-H band in the ligand spectrum indicates that the ligand exists predominantly in the thione form.\u003c/p\u003e \u003cp\u003eThe appearance of new bands in the regions 532\u0026ndash;603 cm⁻\u0026sup1; and 414\u0026ndash;469 cm⁻\u0026sup1; in the spectra of the complexes were assigned to ν(M-S) and ν(M-N) vibrations, respectively, further confirming bidentate coordination through sulfur and nitrogen atoms [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]; [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Bands observed in the range 300\u0026ndash;360 cm⁻\u0026sup1; were attributed to ν(M-Cl) stretching vibrations, supporting the coordination of chloride ions. Broad absorption bands between 3340\u0026ndash;3476 cm⁻\u0026sup1; were assigned to ν(O-H) stretching of coordinated water molecules, consistent with the hydrated nature of the complexes indicated in their empirical formulas [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eElectronic Spectral Studies\u003c/h2\u003e \u003cp\u003eThe electronic spectra (Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) of the thiosemicarbazone ligand and its Mn(II), Fe(II), and Co(II) complexes recorded in DMSO exhibit characteristic π\u0026rarr;π* and n\u0026rarr;π* transitions associated with the C\u0026thinsp;=\u0026thinsp;N and C\u0026thinsp;=\u0026thinsp;S chromophores. The free ligand shows intense bands at 242 and 266 nm attributed to π\u0026rarr;π* transitions, and bands at 327 and 347 nm assigned to n\u0026rarr;π* transitions. Upon coordination, these bands undergo slight bathochromic shifts accompanied by changes in absorbance intensity, indicating involvement of the azomethine nitrogen and thione sulfur atoms in metal\u0026ndash;ligand bonding. The observed spectral shifts reflect modification of the ligand electronic environment due to coordination. The absence of well-resolved d\u0026ndash;d transitions is attributed to their low intensity and overlap with ligand-centered transitions. Overall, the electronic spectral data support complex formation and are consistent with the proposed octahedral geometry of the metal(II) complexes.\u003c/p\u003e \u003cp\u003eIn octahedral complexes, d\u0026ndash;d transitions are formally Laporte forbidden and therefore intrinsically low in intensity; such transitions become weakly allowed through vibronic coupling and other symmetry-breaking mechanisms. These low-intensity d\u0026ndash;d bands are often masked by more intense ligand-centered π\u0026rarr;π* and n\u0026rarr;π* absorptions in the UV\u0026ndash;visible region, resulting in poorly resolved or overlapping spectral features in the electronic spectra of the complexes.\u003c/p\u003e \u003cp\u003eCollectively, the physicochemical, magnetic, spectroscopic, and analytical results conclusively demonstrate that the thiosemicarbazone ligand (L) coordinates in a bidentate manner through azomethine nitrogen and thione sulfur atoms. The remaining coordination sites are occupied by chloride ions and water molecules, resulting in stable six-coordinate octahedral Mn(II), Fe(II), and Co(II) complexes.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab8\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 8\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAntibacterial Activity (Zone of Inhibition, mm) of the Schiff base Ligand (L) and its Mn(II), Fe(II), and Co(II) Complexes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCompound\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eConcentration (\u0026micro;g/mL)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eGram-positive Bacteria (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eGram-negative Bacteria (mm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eStaphylococcus aureus\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eEscherichia coli\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eSalmonella typhi\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eThiosemicarbazone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e07\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e[Mn(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e[Fe(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e[Co(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e09\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCiprofloxacin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003eL\u0026thinsp;=\u0026thinsp;C\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e11\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003eS\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab9\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 9\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAntifungal Activity (Zone of Inhibition, mm) of the Schiff base Ligand (L) and its Mn(II), Fe(II), and Co(II) Complexes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCompound\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eConcentration (\u0026micro;g/mL)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eFungi\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eCandida Albicans\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eTinea pedis\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eAspergillus flavus\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eThiosemicarbazone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e07\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e[Mn(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e09\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e[Fe(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e[Co(L)\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e ].2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKetoconazole\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003eL\u0026thinsp;=\u0026thinsp;C\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e11\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003eS\u003c/h2\u003e \u003cdiv id=\"Sec25\" class=\"Section3\"\u003e \u003ch2\u003eAntimicrobial activity\u003c/h2\u003e \u003cp\u003eThe antimicrobial evaluation clearly shows that coordination of the thiosemicarbazone ligand with Mn(II), Fe(II), and Co(II) ions leads to a consistent improvement in both antibacterial and antifungal activities. In all cases, the metal complexes produced larger zones of inhibition than the free ligand, highlighting the central role of metal coordination in enhancing biological performance. This improvement is reasonably attributed to chelation, which reduces the polarity of the ligand and increases overall lipophilicity, thereby facilitating penetration across microbial cell membranes [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eBacterial susceptibility was strongly influenced by cell wall structure. The Gram-positive \u003cem\u003eStaphylococcus aureus\u003c/em\u003e exhibited greater sensitivity than the Gram-negative strains, consistent with the absence of an outer lipopolysaccharide barrier. Among the complexes, the Fe(II) and Co(II) derivatives showed the highest activity against \u003cem\u003eS. aureus\u003c/em\u003e, suggesting that their electronic configurations and redox characteristics favor effective intracellular disruption. In contrast, \u003cem\u003eEscherichia coli\u003c/em\u003e and \u003cem\u003eSalmonella typhi\u003c/em\u003e displayed lower susceptibility, reflecting the additional permeability barriers and efflux mechanisms typical of Gram-negative bacteria. Notably, the Mn(II) complex demonstrated comparatively enhanced activity against \u003cem\u003eE. coli\u003c/em\u003e, indicating that the nature of the metal center can influence selectivity, possibly through differences in uptake pathways or interactions with bacterial transport systems.\u003c/p\u003e \u003cp\u003eThe antifungal results further support the beneficial impact of metal coordination. All metal complexes showed improved activity against \u003cem\u003eCandida albicans\u003c/em\u003e, \u003cem\u003eTinea pedis\u003c/em\u003e, and \u003cem\u003eAspergillus flavus\u003c/em\u003e compared with the free ligand, although ketoconazole remained the most active reference compound. The Co(II) complex exhibited the strongest antifungal effect, particularly against \u003cem\u003eT. pedis\u003c/em\u003e, where its activity closely approached that of the standard drug. Against the more resistant \u003cem\u003eA. flavus\u003c/em\u003e, moderate but meaningful enhancement was observed upon complexation, demonstrating that metal coordination can broaden antifungal activity even against less susceptible fungal species [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eAcross all microbial assays, larger inhibition zones were consistently observed at lower test concentrations. This trend is likely associated with improved diffusion and reduced aggregation of the complexes in the agar medium, emphasizing that physicochemical behavior plays an important role in determining apparent biological activity. Overall, the antimicrobial effectiveness followed the trend Fe(II)\u0026thinsp;\u0026asymp;\u0026thinsp;Co(II)\u0026thinsp;\u0026gt;\u0026thinsp;Mn(II)\u0026thinsp;\u0026gt;\u0026thinsp;free ligand, underscoring the importance of metal identity in modulating potency and spectrum of activity[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section3\"\u003e \u003ch2\u003eProposed mechanism of antimicrobial action\u003c/h2\u003e \u003cp\u003eThe enhanced antimicrobial activity of the metal complexes appears to arise from a combination of physicochemical and biochemical effects. Chelation increases lipophilicity and membrane permeability, allowing more efficient intracellular access. Once inside the cell, the metal centers may interfere with essential biological processes through enzyme inhibition, displacement of native metal ions from proteins, and redox-mediated generation of reactive oxygen species. The resulting oxidative damage to membranes, proteins, and nucleic acids likely contributes to the superior antibacterial and antifungal activities observed for the metal complexes relative to the uncoordinated ligand [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003eA novel pyrrole-based thiosemicarbazone Schiff base ligand was successfully synthesized and coordinated with Mn(II), Fe(II), and Co(II) ions to yield stable transition metal complexes. Detailed physicochemical and spectroscopic analyses confirmed that the ligand coordinates in a bidentate manner through the azomethine nitrogen and thione sulfur atoms, resulting in six-coordinate octahedral geometries for all the complexes. Magnetic susceptibility measurements indicated high-spin configurations, fully consistent with the proposed structures, while the low molar conductance values verified the non-electrolytic nature of the complexes.\u003c/p\u003e \u003cp\u003eMetal coordination significantly improved the thermal stability of the ligand and induced noticeable changes in its electronic properties, as reflected by higher decomposition temperatures and diagnostic spectral shifts. The proposed compositions and purity of the synthesized compounds were further supported by elemental analysis and atomic absorption spectroscopy.\u003c/p\u003e \u003cp\u003eBiological screening demonstrated that the metal complexes exhibit markedly enhanced antibacterial and antifungal activities compared to the free ligand, with the Fe(II) and Co(II) complexes showing the strongest inhibitory effects. This improvement in antimicrobial performance is attributed to chelation, which increases lipophilicity and facilitates penetration through microbial cell membranes, along with potential metal-mediated interactions that disrupt essential intracellular processes. The observed variation in activity among the complexes highlights the critical role of the metal ion in modulating biological efficacy.\u003c/p\u003e \u003cp\u003eOverall, the findings confirm that pyrrole-based thiosemicarbazone ligands are effective chelating systems for the generation of biologically active transition metal complexes. This work provides meaningful insights into structure\u0026ndash;property\u0026ndash;activity relationships and supports the continued development of thiosemicarbazone metal complexes as promising candidates for antimicrobial applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eEthics Approval and Consent to Participate\u003c/h2\u003e\n\u003cp\u003eThis study did not involve human participants or animals. Ethical approval and consent to participate were therefore not required.\u003c/p\u003e\n\u003ch2\u003eConsent to Publish\u003c/h2\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003ch2\u003eFunding\u003c/h2\u003e\n\u003cp\u003eThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eThe author conceptualize the study, carried out the synthesis and Characterization of the ligand and metal complexes, performed the biological experiments, analyzed and interpreted the data and wrote the original draft of the manuscript. The author also reviewed and approved the final version of the manuscript.\u003c/p\u003e\n\u003ch2\u003eAcknowledgement\u003c/h2\u003e\n\u003cp\u003eI acknowledge the guidance and support rendered by both the technical and academic staff of Bayero University, kano\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBandyopadhyay D, Banik BK. Heterocycles in medicinal chemistry. Curr Org Chem. 2015;19(3):252\u0026ndash;76.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJamp\u0026iacute;lek J. Heterocyclic scaffolds in modern drug design. Eur J Med Chem. 2024;251:115226.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLeśniewska A, Kaczmarek M, Ptaszyński K. Nitrogen- and sulfur-donor ligands in coordination chemistry. Dalton Trans. 2024;53:4452\u0026ndash;68.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZeleke D, Mekonnen T, Tadesse S. Donor atom effects in transition metal coordination. 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Molecules. 2023;28(9):4123.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAdhao V, Wagh P. Thermal behavior and stability of Schiff base metal complexes. J Therm Anal Calorim. 2024;149:1123\u0026ndash;35.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSharma VK, Reddy MS, Chandra S. Solubility and non-electrolytic nature of metal chelates. J Mol Liq. 2021;334:116071.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePhilippi F, Rauber D, Welton T. Solvent effects on conductivity measurements. Chem Sci. 2022;13(6):2735\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEl-Sonbati AZ, Diab MA, El-Bindary AA. Conductometric studies of transition metal complexes. Spectrochimica Acta Part A. 2021;246:118980.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNartop D, Yıldız E, Kaya M. Conductivity behavior of non-electrolytic metal complexes. Inorg Chem Commun. 2024;157:110989.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMoustafa H, El-Shafie A, Zaki Z. Magnetic susceptibility of Mn(II) complexes. J Magn Magn Mater. 2022;556:169384.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEl-Ghamry MA, Abdel-Kader NS, Issa RM. Magnetic properties of octahedral Co(II) complexes. Inorg Chem Commun. 2022;136:109132.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGraur V, Chumakov Y, Gulea A. (2023). Structural characterization of metal\u0026ndash;thiosemicarbazone complexes. \u003cem\u003eBioinorganic Chemistry and Applications, 2023\u003c/em\u003e, Article 2705332.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOlayanju O, Bello A, Lawal M. Atomic absorption analysis of transition metal complexes. J Anal Chem. 2025;80(1):54\u0026ndash;61.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIsyaku U, Musa AY, Sadiq AA. Infrared spectral assignments in metal\u0026ndash;ligand complexes. J Mol Struct. 2020;1217:128431.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMarimaran B, Thirumaran S, Kumaravel S. Metal\u0026ndash;sulfur and metal\u0026ndash;nitrogen vibrational studies. Spectrochimica Acta Part A. 2021;252:119503.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShebl M, Naglah AM. Coordination behavior of hydrated metal complexes. J Coord Chem. 2020;73(18):2567\u0026ndash;83.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHu X, Sun L, Nie T, et al. Evaluation of agar dilution method in antimicrobial susceptibility testing. Antibiotics. 2022;11(10):1392.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBalouiri M, Sadiki M, Ibnsouda SK. Methods for in vitro evaluating antimicrobial activity: A review. J Pharm Anal. 2016;6(2):71\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAly AA, Mohamed AA, El-Sayed MA. Metal\u0026ndash;ligand chelation and its role in antimicrobial activity. Appl Organomet Chem. 2023;37(5):e7064.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQamar HMG, Bashir T, Ibrahim U, et al. Antibacterial activity of transition metal thiosemicarbazone complexes. Futuristic Biotechnol. 2024;4(3):62\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Schemes","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Chemistry](https://link.springer.com/journal/44371)","snPcode":"44371","submissionUrl":"https://submission.nature.com/new-submission/44371/3","title":"Discover Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Synthesis, Schiff base, 4-methyl-3-thiosemicarbazide, pyrrole-2-carboxaldehyde, antimicrobial activity, octahedral geometry","lastPublishedDoi":"10.21203/rs.3.rs-8484646/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8484646/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA new Schiff base ligand was synthesized via the condensation of 4-methyl-3-thiosemicarbazide with 1H-pyrrole-2-carboxaldehyde and subsequently coordinated with Mn(II), Fe(II), and Co(II) ions. The ligand and its metal complexes were characterized using FT-IR, UV\u0026ndash;Visible spectroscopy, elemental analysis, magnetic susceptibility, molar conductance, and melting/decomposition temperature determination. Infrared spectral shifts of the azomethine ν(C\u0026thinsp;=\u0026thinsp;N) band, together with the appearance of metal\u0026ndash;nitrogen and metal\u0026ndash;sulfur vibrational bands, confirm coordination through the azomethine nitrogen and thione sulfur atoms. Electronic and magnetic data support a high-spin octahedral geometry for all complexes. The complexes exhibit improved thermal stability and low molar conductance values, indicating non-electrolytic behavior. Antimicrobial evaluation against \u003cem\u003eStaphylococcus aureus\u003c/em\u003e, \u003cem\u003eEscherichia coli\u003c/em\u003e, \u003cem\u003eSalmonella typhi, Candida albican\u003c/em\u003e, \u003cem\u003eTinea pedis\u003c/em\u003e and \u003cem\u003eAspergillus flavus\u003c/em\u003e revealed enhanced activity for the metal complexes relative to the free ligand, highlighting the role of chelation in modulating biological efficacy.\u003c/p\u003e","manuscriptTitle":"Synthesis, Characterization, and Antimicrobial Evaluation of Mn(II), Fe(II), and Co(II) Complexes of a Pyrrole-Based Thiosemicarbazone Schiff Base","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-07 12:16:37","doi":"10.21203/rs.3.rs-8484646/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-01-21T08:53:00+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-06T06:26:10+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-01-06T06:25:47+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Chemistry","date":"2025-12-30T23:39:34+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Chemistry](https://link.springer.com/journal/44371)","snPcode":"44371","submissionUrl":"https://submission.nature.com/new-submission/44371/3","title":"Discover Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"353f83d3-d672-4d40-aa35-38d67a26b336","owner":[],"postedDate":"January 7th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-02-04T14:54:55+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-07 12:16:37","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8484646","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8484646","identity":"rs-8484646","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}