Synthesis, Spectroscopic Characterization, Thermal Behavior, and Antimicrobial and its Evaluation of Schiff Base Transition Metal Complexes Derived from Isonicotinic Acid Hydrazide

Synthesis, Spectroscopic Characterization, Thermal Behavior, and Antimicrobial and its Evaluation of Schiff Base Transition Metal Complexes Derived from Isonicotinic Acid Hydrazide | 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, Spectroscopic Characterization, Thermal Behavior, and Antimicrobial and its Evaluation of Schiff Base Transition Metal Complexes Derived from Isonicotinic Acid Hydrazide Shalini Yadav, Dhirendra Yadav, Poonam Verma, Vinod Kumar This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7945567/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract A novel Schiff base ligand, isonicotinic acid [1-(3,4-dimethoxyphenyl) ethylidene] hydrazide (INADPEH), was synthesized from condensation of isonicotinic acid hydrazide with 1-(3,4-dimethoxyphenyl)ethan-1-one. The Schiff base and its metal (Cobalt, Copper, Nickle, and Iron) complexes were characterized by elemental analysis, molar conductivity, magnetic moment values, UV-Vis, FTIR, and thermogravimetric analysis (TGA), and were obtained in good yields. The structure of the ligand was also confirmed by 1 H NMR spectroscopy. Analytical and spectral data confirmed that INADPEH acts as a bidentate ligand, coordinating through the azomethine nitrogen and carbonyl oxygen. FTIR and UV-Vis spectra and magnetic susceptibility values collectively suggested predominantly octahedral geometries for the complexes. Thermal studies indicated stepwise decomposition of the complexes, with metal oxides as final residues. The antimicrobial activities of the compounds were tested against Escherichia coli, Staphylococcus aureus, Candida albicans , and Aspergillus niger. The antibacterial activity results revealed that the free ligand showed lower activity compared to the cobalt and copper complexes, with the copper complex exhibiting highest potency, surpassing the standard in some cases. This study highlights the enhanced biological efficacy arising from the significant role of metal complexation and recommends the potential applications of these hydrazone metal complexes as antimicrobial agents. Schiff base Transition metal complexes Spectral characterization Thermal stability Antimicrobic activity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Schiff bases ligand and their transition metal complexes have gained significant interest because of their diverse structures, flexible coordination abilities, and broad practical uses in fields such as catalysis, materials science, and medicinal chemistry [ 1 – 2 ]. The azomethine group (-C = N-) not only helps stabilize the ligand but also plays a crucial role in influencing biological activities. Various transition metal complexes of Schiff bases have been found to show remarkable antibacterial, antifungal, anticancer, and antioxidant effects compared to the original ligands from which they are derived [ 3 ]. Isonicotinic acid hydrazide derivatives are of particular pharmacological relevance due to their antimicrobial activity and potential as anti-tubercular agents. Coordination of such ligands with transition metals is known to significantly modify their physicochemical and biological properties [ 4 ]. In this study, we report the synthesis, spectral and thermal characterization, and antimicrobial evaluation of Schiff base complexes derived from isonicotinic acid hydrazide 1-(3,4-dimethoxyphenyl)ethan-1-one. 2. Materials and Methods All the chemicals employed were of analytical grade, and the solvents were purified before use. Metal salts CoCl 2 ·6H 2 O, CuCl 2 ·2H 2 O, NiCl 2 ·6H 2 O and FeCl 3 ·6H 2 O were obtained commercially. 2.1. Scheme of Ligand Synthesis The ligand INADPEH was obtained by refluxing equimolar amounts of isonicotinic acid hydrazide with 1-(3,4-dimethoxyphenyl)ethan-1-one in ethanol for 8 h. The product was filtered and then washed with ethanol and air dried. Yield: 81.4%, M.P. 185–189 ℃. 2.2. Synthesis of Metal Complexes The metal complexes formation was achieved by refluxing the Schiff base ligand and appropriate metal salts in ethanol at a 2:1 molar ration for 2 hours. The products were subsequently filtered, washed with ethanol and dried in vacuo. 2.3. Analytical and Physical Measurements Elemental analysis (C, H, N) was performed by using Elementar Vario EL cube V4.0.11 Elementar Analysensysteme GmbH, molar conductance (10 − 4 M, DMSO), FTIR (KBr pellets, (at 4000 − 400 cm -1) , 1 H NMR (DMSO-d 6 ), UV-Vis (methanol, 10 − 3 M), magnetic susceptibility, TGA (N 2 gas, 30–800 ℃ and 20 ℃/min), and PXRD (Cu-Kα radiation) were employed for the characterization of the Schiff base ligand and its metal complexes. Chlorine content in the metal complexes was determined using Mohr’s method, and the results were consistent with the proposed molecular formulae. 2.4. Antimicrobial Studies Antibacterial (tested against S. aureus and E. coli ) and antifungal (against C. albicans and A.niger) activities were assessed by the agar well diffusion method at concentrations of 20–80 µl (10 mg/ml solutions). Ciprofloxacin and Ketoconazole served as standard drugs. 3. Results and Discussion 3.1. Analytical and Physical Data When analyzing the composition of the ligand and its corresponding metal complexes, the results matched up closely with what theory predicted, confirming that these compounds formed just as intended [ 5 ]. The yields for the complexes were above 34 percent and they didn’t break down until hitting pretty sharp melting point, elevated temperatures, which means they’re slightly tough against heat. It’s interesting how the appearance changed: the ligand itself was a soft yellow, but once it mixed with metals, each complex took on its own bold color—cobalt looked blush purple, copper turned olive green, nickel gave off a lavender shade, and iron settled into brown. These colors reflect what's happening inside their structures, with d-d transitions and charge-transfer effects that are distinct for transition metals. Looking at molar conductivity (between 46 and 60.7 Ω⁻¹cm²mol⁻¹), most of these complexes didn’t behave like typical electrolytes, except for the iron(III) compound, which was a bit higher just as expect for its structure, [FeL₂Cl₂]Cl. What this means is that chloride ions are bound to the metal in cobalt, copper, and nickel complexes, while iron keeps one chloride out as a counter-ion, which lines up with what’s been reported for similar octahedral iron complexes in previous researches [ 6 – 7 ]. Table 1 Physico-chemical parameter and analytical data of ligand and its metal complexes Compounds Name Color Yield Melting Point Observed (Theoretical %) Molar conductivity ˄m (mol − 1 cm 2 ohm − 1 ) C H N Cl Ligand, L (C 16 H 17 N 3 O 3 ) Pale yellow 81.4% 185–189 64.69 (64.20) 5.64 (5.72) 14.95 (14.04) - 60.7 CoL 2 Cl 2 Blush Purple 44.5% > 250 52.69 (52.76) 4.64 (4.7) 10.95 (11.54) 9.63 (9.73) 55.3 CuL 2 Cl 2 Olive Green 61.25% > 250 51.81 (52.43) 4.15 (4.67) 11.65 (11.46) 9.54 (9.67) 46 NiL 2 Cl 2 Light Lavendra 74.3% > 250 51.81 (52.78) 4.15 (4.71) 11.45 (11.54) 9.66 (9.76) 56.7 [FeL 2 Cl 2 ]Cl Brown 34.2% > 250 51.81 (52.98) 4.15 (4.72) 11.29 (11.59) 9.74 (9.77) 52.4 3.2. FTIR Spectral Analysis The FTIR spectra of the Schiff base ligand showed a distinct azomethine (ν C = N) band at 1541 cm -1 . Upon complexation, this absorption band which shifted to lower frequency range (1509–1549 cm -1 ). These observed shift suggests the involvement of the azomethine nitrogen in binding to the metal ion [ 8 ]. Similarly, the carbonyl band ν C = O of the Schiff base ligand appeared at 1665 cm -1 and showed a shift in the complexes, suggesting bonding through the carbonyl oxygen [ 9 – 10 ]. The amide N-H stretching band remained unaffected, excluding its involvement in coordination. In addition, new absorption bands corresponding to ν M-N (759–767 cm -1 ), ν M-O (533-657cm -1 ), and ν M-Cl (428–509 cm -1 ) appeared in the complexes, these results provide additional confirmation of bidentate binding through the azomethine nitrogen and carbonyl oxygen [ 11 – 12 ]. The observation is consistent with earlier studies where Schiff bases derived form hydrazides typically acts as bidentate ligands, stabilizing octahedral geometries around transition metals. Table 2. Selected FTIR spectral data ν(cm − 1 ) of Schiff base ligand and its complexes Name ν C = N ν C = O ν M-N ν M-O ν M-Cl Isonicotinic Acid [1-(3,4-dimethoxy-phenyl) ethylidene]Hydrazide 1541 1665 - - - Complex-Co(II) 1549 1651 760 539 428 Complex-Cu(II) 1510 1670 765 545 466 Complex-Ni(II) 1509 1651 767 533 454 Complex-Fe(III) 1543 1651 759 657 509 3.3. 1 H NMR Spectroscopy The 1 H NMR spectral of the ligand (L) recorded in DMSO- d 6 displayed expected chemical shifts for all protons. Singlets corresponding to the methoxy (δ 3.48 and 3.82 ppm) and methyl (δ 2.37 ppm) groups confirmed substitution on the aromatic ring. The aromatic and pyridine protons appeared in the δ 7.0-8.7 ppm range. Importantly, a broad singlet observed at δ 11.09 ppm was attributed to the amidic proton, confirming condensation between the hydrazide and ketone moieties [ 13 ]. The absence of any aldehydic proton resonance further substantiated Schiff base formation. 3.4. Magnetic Moments and Electronic Spectral Studies The electronic spectra of the Schiff base ligand showed bands at λ max 258 and 385 nm, assignable to π- π * and n-π * transitions of the azomethine group. The coordination of ligand with metal showed band shifts to longer wavelengths, indicating ligand-to-metal charge transfer (LMCT). The Co(II) complex displayed multiple bands at λ max 231, 335, 516, and 593 nm and assignable were respectively to LMCT, d-d transitions 4 T 1g (F) → 4 T 1g (P) , 4 T 1g (F) → 4 T 2g (F) , and 4 T 1g (F) → 4 A 2g (F) , confirming an octahedral geometry. The magnetic moment (4.87 BM) was consistent with a high-spin Co(II) configuration [ 8 ]. Cu(II) complex exhibited a broad absorption at λ max 278, 312 nm, attributed to LMCT. The absence of well-resolved d-d bands is typical of distorted octahedral Cu(II) complexes due to Jahn-Teller distortion. The magnetic moment (1.87 BM) confirmed one unpaired electron [ 14 ]. Ni(II) complex exhibited absorption bands at λ max 262, 350 and 564 nm, which were assigned to LMCT, 3 A 2g (F) → 3 T 1g (P) , and 3 A 2g (F) → 3 T 1g (F) transitions respectively, which supported an octahedral geometry. The moment (2.96 BM) was consistent with two unpaired electrons [ 15 ]. For Fe(III) complex displayed weak d-d transitions at λ max 265 and 393 nm along with LMCT and 6 A 1 → 4 T 2 (G) bands, consistent with a high-spin octahedral d 5 system. The magnetic moment (1.58 BM) was lower than expected, possibly due to antiferromagnetic interaction [ 16 ]. These observations establish that all metal complexes adopt octahedral geometries, whereas Cu(II) showing a distorted environment. Table 4 Electronic spectral and magnetic moment data of Schiff base ligand and its complexes with corresponding assignments Compounds name M.M Absorption band positions (nm) Possible transitions Geometry Ligand (C 16 H 17 N 3 O 3 ) - 258, 385 π-π* and n-π* - CoL 2 Cl 2 4.87 231, 335, 516, 593 LMCT, 4 T 1g (F)→ 4 T 1g (P) , 4 T 1g ​(F) → 4 T 2g (F) , and 4 T 1g (F)→ 4 A 2g (F) octahedral CuL 2 Cl 2 1.87 278, 312 (LMCT) distorted octahedral NiL 2 Cl 2 2.96 262, 350, 564 LMCT, 3 A 2g (F) → 3 T 1g (P) and 3 A 2g (F) → 3 T 1g (F) octahedral [FeL 2 Cl 2 ]Cl 1.58 393, 265 6 A 1 → 4 T 2 (G) and LMCT octahedral Figure 4 . UV-Vis spectrum of ligand (isonicotinic acid [1-(3,4-dimethoxyphenyl) ethylidene] hydrazide) and its metal complexes 3.5. Thermal Studies (TGA) Thermogravimetric analysis (TGA) confirmed multiple decomposition steps of all complexes. Co(II) complex was stable up to 200 ℃ and a major decomposition event between 400–600 ℃ results in 51.7% weight loss (calcd. 51.1%), corresponding to the degradation of the compound’s organic framework and stepwise decomposition gave the residue of metal oxide CoO. Cu(II) complex exhibited a major weight loss (70.9%) between 150–400 ℃ corresponded to ligand and decomposition and the final residue observed as metal oxide (CuO). Ni(II) complex was undergoing nearly complete degradation (95% weight loss) and left the metal oxide as a residue (NiO). For Fe(III) complex which followed by a major decomposition of the organic framework between 300–600°C. final residue matched Fe 3 O 4 (29.1%), consistent with magnetite formation at high temperature. The close match between observed and calculated weight losses confirmed the proposed compositions [ 17 ]. Complexation with metal ions enhanced the thermal stability of the ligand, particularly delaying major decomposition beyond 300 ℃, suggesting strong coordination and potential for high-temperature applications. 3.6. PXRD (Powder X-ray Diffraction) The crystalline nature of the complexes was confirmed by PXRD analysis. Crystalline sizes estimated using by the Scherrer equation ranged from 27.4 to 50.7 nm, placing them in the nanocrystalline regime [ 18 ]. Such nanoscale crystallinity is of interest since it can significantly influence both the catalytic and biological properties of metal complexes, enhancing their reactivity and antimicrobial potential. The crystallite sizes of the ligand and its metal complexes were estimated using the Scherrer equation, and the results are summarized in Table 5 . The free Schiff base ligand exhibited a crystallite size of 44.4 nm which confirming its nanocrystalline nature. Upon coordination with transition metal ions, significant variations in crystallite size were observed. The Co(II) (32.8) and Cu(II) (27.4) complexes displayed reduced crystallite sizes in comparison to the ligand, indicating that metal coordination causes lattice strain and limits crystallite development. In comparison, the Ni(II) complex (41 nm) displayed a size similar to that of the ligand, suggesting that the incorporation of Ni(II) does not significantly change the dimensions of the crystalline domain. Notably, the Fe(III) complex (50.7 nm) demonstrated the greatest crystallite size, indicating improved crystallinity and superior lattice arrangement in the iron-coordinated system. In general, the sizes of the Schiff base complex crystallites range from 27 to 51 nm, and the noted differences are due to variations in ionic radii, coordination geometry, and the extent of distortion caused by the specific metal ions [ 18 ]. These results emphasize the impact of metal coordination on the crystalline characteristics of Schiff base complexes, which could subsequently influence their stability and functional attributes Table 5 Ligand and its complexes of crystallite size Complex 2θ Crystallite size Ligand, L C 16 H 17 N 3 O 3 12.8141 degrees 444.37 Å (44.44 nm) Cobalt 29.692 degrees 327.74 Å (32.8 nm) Copper 15.475 degrees 273.97 Å (27.4 nm) Nickle 12.6746 degrees 410 Å (41.0 nm) Iron 29.695 degrees 507.32 Å (50.7 nm) 3.7. Antimicrobial Activity The results of the antimicrobial activity showed a distinct improvement with metal complexation when compared to the free ligand tested against Escherichia coli, Staphylococcus aureus, Candida albicans , and Aspergillus niger. The Co(II) complex exhibited highest activity (20 mm at 80 µl), while the copper showed 13 mm. The free ligand showed weak inhibition (8 mm), while Ni(II) was inactive. Dose-dependent antibacterial activity was observed for the cobalt and copper complexes, whereas the ligand was inactive against S. aureus. The Cu(II) complex showed remarkable activity (20 mm) against C. albicans , nearly comparable to the standard drug ketoconazole, while Co(II) was moderately active. Against A. niger , Cu(II) complex surpassed even the standard drug at higher concentrations (24 mm vs 23 mm), highlighting its strong antifungal potential. The enhanced antimicrobial effect of cobalt and copper complexes can be attributed to increased lipophilicity upon chelation, which facilitates penetration of microbial cell membranes [ 19 ]. Additionally, transition metal ions may promote redox reactions inside microbial cells, disrupting DNA or protein functions. The relatively weak activity of the Ni(II) complex suggests that the geometry and electronic properties of the metal center strongly influence biological activity [ 20 , 3 ]. Table 6 Diameter of inhibition zone (mm) of Schiff base ligand and its complexes against E. coli and S. aureus bacteria S. No. Samples Activity against E. coli bacteria Activity against S. aureus bacteria Diameter of inhibition zone (mm) Diameter of inhibition zone (mm) Standard 20 µl 40 µl 60 µl 80 µl Standard 20 µl 40 µl 60 µl 80 µl 1 Ligand (C 16 H 17 N 3 O 3 ) 33 - - - 8 28 - - - - 2 CoL 2 Cl 2 33 11 13 15 20 28 - 10 12 14 3 CuL 2 Cl 2 33 - 9 11 13 28 - 9 10 12 4 NiL 2 Cl 2 33 - - - - 28 - - - 9 Table 7 Diameter of inhibition zone (mm) of Schiff base ligand and its complexes against C. albicans and A. niger fungal S. No. Samples Activity against C. albicans fungal Activity against A. niger fungal Diameter of inhibition zone (mm) Diameter of inhibition zone (mm) Standard 20 µl 40 µl 60 µl 80 µl Standard 20 µl 40 µl 60 µl 80 µl 1 Ligand (C 16 H 17 N 3 O 3 ) 23 - - - - 31 - 11 12 15 2 CoL 2 Cl 2 23 - - 9 11 31 - 9 13 17 3 CuL 2 Cl 2 23 11 16 18 20 31 13 16 21 24 4 NiL 2 Cl 2 23 - - - 10 31 - - - 9 4. Conclusion A new Shiff base ligand and its transition metal complexes were successfully synthesized and comprehensively characterized. Spectral and thermal studies confirmed octahedral coordinated, while PXRD indicated nanoscale crystallinity. Antimicrobial evaluation demonstrated that Co(II) and Cu(II) complexes exhibit promising antibacterial and antifungal activity, with Cu(II) showing superior efficacy. These results highlight the potential of Schiff base transition metal complexes as leads for developing novel antimicrobial agent. Declarations Author Contribution Author ContributionsShalini Yadav: Conducted the entire research work, including conceptualization, synthesis of the ligand and metal complexes, characterization, data analysis, antimicrobial studies, and manuscript preparation.Dhirendra Yadav: Assisted in conceptualization and provided guidance during data interpretation.Poonam Verma: Supported experimental design and contributed to manuscript review and editing.Vinod Kumar: Supervised the research, provided overall guidance, and reviewed the final manuscript. Acknowledgements The authors gratefully acknowledge SMS Medical College, Jaipur, for providing microbial strains and laboratory facilities. References Abu-Dief AM, Mohamed, IMA (2015) A review on versatile applications of transition metal complexes incorporating Schiff bases. 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10:24:47","extension":"xml","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":87391,"visible":true,"origin":"","legend":"","description":"","filename":"d668425ca7f34905afdd952827d73ac51structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7945567/v1/1daab5f9e9b9fce807dcdaaa.xml"},{"id":95103649,"identity":"9ca798de-e195-466a-b291-ed57ce983dd1","added_by":"auto","created_at":"2025-11-04 10:24:32","extension":"html","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":96170,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7945567/v1/ba9fce6dcd3ae291f85a36e6.html"},{"id":95103640,"identity":"e172763e-d373-40d9-94a8-7b2a2bafbbe6","added_by":"auto","created_at":"2025-11-04 10:24:31","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":42393,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme for the synthesis of the ligand\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7945567/v1/84a1df2f27581147ecf529a9.png"},{"id":95103658,"identity":"1afd0db6-d26b-4e01-9629-974b6ec47878","added_by":"auto","created_at":"2025-11-04 10:24:34","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":45396,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSynthesis of Schiff base metal complexes\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7945567/v1/86c1d950353513752d184b50.png"},{"id":95103661,"identity":"df96b839-bd33-4a22-a501-e53ce2292365","added_by":"auto","created_at":"2025-11-04 10:24:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":113693,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eIR spectrum of ligand (isonicotinic acid [1-(3,4-dimethoxyphenyl) ethylidene] hydrazide) and their transition metal complexes\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7945567/v1/6f832d91850e477d3e87ccaf.png"},{"id":95225119,"identity":"4e4740dc-e3c6-4b0e-b14b-8428607d4631","added_by":"auto","created_at":"2025-11-05 16:24:36","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":139477,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eUV-Vis spectrum of ligand (isonicotinic acid [1-(3,4-dimethoxyphenyl) ethylidene] hydrazide) and its metal complexes\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7945567/v1/bfba4cdbf08416b5c0c0e22c.png"},{"id":95225356,"identity":"c5ece3fc-d669-4357-a98f-8d4670a22c65","added_by":"auto","created_at":"2025-11-05 16:24:54","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":76795,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eE. coil\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 3. Graph of diameter of inhibition zone (mm) against \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eE. coli and S. aureus\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7945567/v1/94af42c2a7910b14a11ab29b.png"},{"id":95103636,"identity":"9d43c25b-1a57-4b51-aedf-8c2251fa8184","added_by":"auto","created_at":"2025-11-04 10:24:29","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":84129,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 4. Graph of diameter of inhibition zone (mm) against \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eC. albicans and A. niger \u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003efungal\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7945567/v1/7a5671f315b62250b8ea337e.png"},{"id":95230395,"identity":"f2613795-a3e2-4055-9633-9d1c2f1b5902","added_by":"auto","created_at":"2025-11-05 16:37:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1776721,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7945567/v1/bab24442-8872-4aee-874b-1d489b89f679.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Synthesis, Spectroscopic Characterization, Thermal Behavior, and Antimicrobial and its Evaluation of Schiff Base Transition Metal Complexes Derived from Isonicotinic Acid Hydrazide","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eSchiff bases ligand and their transition metal complexes have gained significant interest because of their diverse structures, flexible coordination abilities, and broad practical uses in fields such as catalysis, materials science, and medicinal chemistry [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The azomethine group (-C\u0026thinsp;=\u0026thinsp;N-) not only helps stabilize the ligand but also plays a crucial role in influencing biological activities. Various transition metal complexes of Schiff bases have been found to show remarkable antibacterial, antifungal, anticancer, and antioxidant effects compared to the original ligands from which they are derived [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIsonicotinic acid hydrazide derivatives are of particular pharmacological relevance due to their antimicrobial activity and potential as anti-tubercular agents. Coordination of such ligands with transition metals is known to significantly modify their physicochemical and biological properties [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. In this study, we report the synthesis, spectral and thermal characterization, and antimicrobial evaluation of Schiff base complexes derived from isonicotinic acid hydrazide 1-(3,4-dimethoxyphenyl)ethan-1-one.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eAll the chemicals employed were of analytical grade, and the solvents were purified before use. Metal salts CoCl\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO, CuCl\u003csub\u003e2\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO, NiCl\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO and FeCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO were obtained commercially.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Scheme of Ligand Synthesis\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe ligand INADPEH was obtained by refluxing equimolar amounts of isonicotinic acid hydrazide with 1-(3,4-dimethoxyphenyl)ethan-1-one in ethanol for 8 h. The product was filtered and then washed with ethanol and air dried. Yield: 81.4%, M.P. 185\u0026ndash;189 ℃.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Synthesis of Metal Complexes\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe metal complexes formation was achieved by refluxing the Schiff base ligand and appropriate metal salts in ethanol at a 2:1 molar ration for 2 hours. The products were subsequently filtered, washed with ethanol and dried in vacuo.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Analytical and Physical Measurements\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eElemental analysis (C, H, N) was performed by using Elementar Vario EL cube V4.0.11 Elementar Analysensysteme GmbH, molar conductance (10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e M, DMSO), FTIR (KBr pellets, (at 4000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm\u003csup\u003e-1)\u003c/sup\u003e, \u003csup\u003e1\u003c/sup\u003eH NMR (DMSO-d\u003csub\u003e6\u003c/sub\u003e), UV-Vis (methanol, 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e M), magnetic susceptibility, TGA (N\u003csub\u003e2\u003c/sub\u003e gas, 30\u0026ndash;800 ℃ and 20 ℃/min), and PXRD (Cu-Kα radiation) were employed for the characterization of the Schiff base ligand and its metal complexes. Chlorine content in the metal complexes was determined using Mohr\u0026rsquo;s method, and the results were consistent with the proposed molecular formulae.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4. Antimicrobial Studies\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eAntibacterial (tested against \u003cem\u003eS. aureus\u003c/em\u003e and \u003cem\u003eE. coli\u003c/em\u003e) and antifungal (against \u003cem\u003eC. albicans\u003c/em\u003e and \u003cem\u003eA.niger)\u003c/em\u003e activities were assessed by the agar well diffusion method at concentrations of 20\u0026ndash;80 \u0026micro;l (10 mg/ml solutions). Ciprofloxacin and Ketoconazole served as standard drugs.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Analytical and Physical Data\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eWhen analyzing the composition of the ligand and its corresponding metal complexes, the results matched up closely with what theory predicted, confirming that these compounds formed just as intended [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The yields for the complexes were above 34 percent and they didn\u0026rsquo;t break down until hitting pretty sharp melting point, elevated temperatures, which means they\u0026rsquo;re slightly tough against heat. It\u0026rsquo;s interesting how the appearance changed: the ligand itself was a soft yellow, but once it mixed with metals, each complex took on its own bold color\u0026mdash;cobalt looked blush purple, copper turned olive green, nickel gave off a lavender shade, and iron settled into brown. These colors reflect what's happening inside their structures, with d-d transitions and charge-transfer effects that are distinct for transition metals. Looking at molar conductivity (between 46 and 60.7 Ω⁻\u0026sup1;cm\u0026sup2;mol⁻\u0026sup1;), most of these complexes didn\u0026rsquo;t behave like typical electrolytes, except for the iron(III) compound, which was a bit higher just as expect for its structure, [FeL₂Cl₂]Cl. What this means is that chloride ions are bound to the metal in cobalt, copper, and nickel complexes, while iron keeps one chloride out as a counter-ion, which lines up with what\u0026rsquo;s been reported for similar octahedral iron complexes in previous researches [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\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\u003ePhysico-chemical parameter and analytical data of ligand and its metal 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=\"char\" char=\".\" 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\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eCompounds Name\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eColor\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eYield\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eMelting Point\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"4\" nameend=\"c8\" namest=\"c5\"\u003e\u003cp\u003eObserved\u003c/p\u003e\u003cp\u003e(Theoretical %)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eMolar\u003c/p\u003e\u003cp\u003econductivity\u003c/p\u003e\u003cp\u003e˄m (mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003cp\u003eohm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eC\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eH\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\u003eCl\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLigand, L\u003c/p\u003e\u003cp\u003e(C\u003csub\u003e16\u003c/sub\u003eH\u003csub\u003e17\u003c/sub\u003eN\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePale yellow\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e81.4%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e185\u0026ndash;189\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e64.69\u003c/p\u003e\u003cp\u003e(64.20)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e5.64\u003c/p\u003e\u003cp\u003e(5.72)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e14.95\u003c/p\u003e\u003cp\u003e(14.04)\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\u003e60.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCoL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eBlush Purple\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e44.5%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e52.69\u003c/p\u003e\u003cp\u003e(52.76)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e4.64\u003c/p\u003e\u003cp\u003e(4.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e10.95\u003c/p\u003e\u003cp\u003e(11.54)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e9.63\u003c/p\u003e\u003cp\u003e(9.73)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e55.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCuL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eOlive\u003c/p\u003e\u003cp\u003eGreen\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e61.25%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e51.81\u003c/p\u003e\u003cp\u003e(52.43)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e4.15\u003c/p\u003e\u003cp\u003e(4.67)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e11.65\u003c/p\u003e\u003cp\u003e(11.46)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e9.54\u003c/p\u003e\u003cp\u003e(9.67)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e46\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNiL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLight Lavendra\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e74.3%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e51.81\u003c/p\u003e\u003cp\u003e(52.78)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e4.15\u003c/p\u003e\u003cp\u003e(4.71)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e11.45\u003c/p\u003e\u003cp\u003e(11.54)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e9.66\u003c/p\u003e\u003cp\u003e(9.76)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e56.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e[FeL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e]Cl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eBrown\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e34.2%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e51.81\u003c/p\u003e\u003cp\u003e(52.98)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e4.15\u003c/p\u003e\u003cp\u003e(4.72)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e11.29\u003c/p\u003e\u003cp\u003e(11.59)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e9.74\u003c/p\u003e\u003cp\u003e(9.77)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e52.4\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\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.2. FTIR Spectral Analysis\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe FTIR spectra of the Schiff base ligand showed a distinct azomethine (ν C\u0026thinsp;=\u0026thinsp;N) band at 1541 cm\u003csup\u003e-1\u003c/sup\u003e. Upon complexation, this absorption band which shifted to lower frequency range (1509\u0026ndash;1549 cm\u003csup\u003e-1\u003c/sup\u003e). These observed shift suggests the involvement of the azomethine nitrogen in binding to the metal ion [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Similarly, the carbonyl band ν C\u0026thinsp;=\u0026thinsp;O of the Schiff base ligand appeared at 1665 cm\u003csup\u003e-1\u003c/sup\u003e and showed a shift in the complexes, suggesting bonding through the carbonyl oxygen [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The amide N-H stretching band remained unaffected, excluding its involvement in coordination.\u003c/p\u003e\u003cp\u003eIn addition, new absorption bands corresponding to ν M-N (759\u0026ndash;767 cm\u003csup\u003e-1\u003c/sup\u003e), ν M-O (533-657cm\u003csup\u003e-1\u003c/sup\u003e), and ν M-Cl (428\u0026ndash;509 cm\u003csup\u003e-1\u003c/sup\u003e) appeared in the complexes, these results provide additional confirmation of bidentate binding through the azomethine nitrogen and carbonyl oxygen [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The observation is consistent with earlier studies where Schiff bases derived form hydrazides typically acts as bidentate ligands, stabilizing octahedral geometries around transition metals.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eTable 2. Selected FTIR spectral data ν(cm\u003c/b\u003e\u003csup\u003e\u003cb\u003e\u0026minus;\u0026thinsp;1\u003c/b\u003e\u003c/sup\u003e\u003cb\u003e) of Schiff base ligand and its complexes\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" 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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eName\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eν C\u0026thinsp;=\u0026thinsp;N\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eν C\u0026thinsp;=\u0026thinsp;O\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eν M-N\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eν M-O\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eν M-Cl\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eIsonicotinic Acid [1-(3,4-dimethoxy-phenyl) ethylidene]Hydrazide\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1541\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1665\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eComplex-Co(II)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1549\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1651\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e760\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e539\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e428\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eComplex-Cu(II)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1510\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1670\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e765\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e545\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e466\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eComplex-Ni(II)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1509\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1651\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e767\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e533\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e454\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eComplex-Fe(III)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1543\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1651\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e759\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e657\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e509\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\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.3. \u003csup\u003e1\u003c/sup\u003eH NMR Spectroscopy\u003c/h2\u003e\u003cp\u003eThe \u003csup\u003e1\u003c/sup\u003eH NMR spectral of the ligand (L) recorded in DMSO- d\u003csub\u003e6\u003c/sub\u003e displayed expected chemical shifts for all protons. Singlets corresponding to the methoxy (δ 3.48 and 3.82 ppm) and methyl (δ 2.37 ppm) groups confirmed substitution on the aromatic ring. The aromatic and pyridine protons appeared in the δ 7.0-8.7 ppm range. Importantly, a broad singlet observed at δ 11.09 ppm was attributed to the amidic proton, confirming condensation between the hydrazide and ketone moieties [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The absence of any aldehydic proton resonance further substantiated Schiff base formation.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.4. Magnetic Moments and Electronic Spectral Studies\u003c/h2\u003e\u003cp\u003eThe electronic spectra of the Schiff base ligand showed bands at λ\u003csub\u003emax\u003c/sub\u003e 258 and 385 nm, assignable to π- π\u003csup\u003e*\u003c/sup\u003e and n-π\u003csup\u003e*\u003c/sup\u003e transitions of the azomethine group. The coordination of ligand with metal showed band shifts to longer wavelengths, indicating ligand-to-metal charge transfer (LMCT). The Co(II) complex displayed multiple bands at λ\u003csub\u003emax\u003c/sub\u003e 231, 335, 516, and 593 nm and assignable were respectively to LMCT, d-d transitions \u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F) \u0026rarr;\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(P)\u003c/em\u003e, \u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F) \u0026rarr;\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e2g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F)\u003c/em\u003e, and \u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F) \u0026rarr;\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003e2g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F)\u003c/em\u003e, confirming an octahedral geometry. The magnetic moment (4.87 BM) was consistent with a high-spin Co(II) configuration [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Cu(II) complex exhibited a broad absorption at λ\u003csub\u003emax\u003c/sub\u003e 278, 312 nm, attributed to LMCT. The absence of well-resolved d-d bands is typical of distorted octahedral Cu(II) complexes due to Jahn-Teller distortion. The magnetic moment (1.87 BM) confirmed one unpaired electron [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Ni(II) complex exhibited absorption bands at λ\u003csub\u003emax\u003c/sub\u003e 262, 350 and 564 nm, which were assigned to LMCT, \u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003e2g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F) \u0026rarr;\u003c/em\u003e\u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(P)\u003c/em\u003e, and \u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003e2g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F) \u0026rarr;\u003c/em\u003e\u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F)\u003c/em\u003e transitions respectively, which supported an octahedral geometry. The moment (2.96 BM) was consistent with two unpaired electrons [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. For Fe(III) complex displayed weak d-d transitions at λ\u003csub\u003emax\u003c/sub\u003e 265 and 393 nm along with LMCT and \u003csup\u003e\u003cem\u003e6\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e\u0026rarr;\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(G)\u003c/em\u003e bands, consistent with a high-spin octahedral d\u003csup\u003e5\u003c/sup\u003e system. The magnetic moment (1.58 BM) was lower than expected, possibly due to antiferromagnetic interaction [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. These observations establish that all metal complexes adopt octahedral geometries, whereas Cu(II) showing a distorted environment.\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 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eElectronic spectral and magnetic moment data of Schiff base ligand and its complexes with corresponding assignments\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\u003eCompounds name\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM.M\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eAbsorption band positions\u003c/p\u003e\u003cp\u003e(nm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePossible transitions\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eGeometry\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLigand\u003c/p\u003e\u003cp\u003e(C\u003csub\u003e16\u003c/sub\u003eH\u003csub\u003e17\u003c/sub\u003eN\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e258, 385\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eπ-π* and n-π*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCoL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4.87\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e231, 335, 516, 593\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eLMCT, \u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F)\u0026rarr;\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(P)\u003c/em\u003e,\u003c/p\u003e\u003cp\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e​(F) \u0026rarr;\u003c/em\u003e \u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e2g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F)\u003c/em\u003e, and \u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F)\u0026rarr;\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003e2g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F)\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eoctahedral\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCuL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.87\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e278, 312\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e(LMCT)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003edistorted octahedral\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNiL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e262, 350, 564\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eLMCT,\u003c/p\u003e\u003cp\u003e\u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003e2g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F) \u0026rarr;\u003c/em\u003e \u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(P)\u003c/em\u003e and\u003c/p\u003e\u003cp\u003e\u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003e2g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F) \u0026rarr;\u003c/em\u003e\u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1g\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(F)\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eoctahedral\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e[FeL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e]Cl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.58\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e393, 265\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003csup\u003e\u003cem\u003e6\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e\u0026rarr;\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(G)\u003c/em\u003e and LMCT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eoctahedral\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. \u003cb\u003eUV-Vis spectrum of ligand (isonicotinic acid [1-(3,4-dimethoxyphenyl) ethylidene] hydrazide) and its metal complexes\u003c/b\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.5. Thermal Studies (TGA)\u003c/h2\u003e\u003cp\u003eThermogravimetric analysis (TGA) confirmed multiple decomposition steps of all complexes. Co(II) complex was stable up to 200 ℃ and a major decomposition event between 400\u0026ndash;600 ℃ results in 51.7% weight loss (calcd. 51.1%), corresponding to the degradation of the compound\u0026rsquo;s organic framework and stepwise decomposition gave the residue of metal oxide CoO. Cu(II) complex exhibited a major weight loss (70.9%) between 150\u0026ndash;400 ℃ corresponded to ligand and decomposition and the final residue observed as metal oxide (CuO). Ni(II) complex was undergoing nearly complete degradation (95% weight loss) and left the metal oxide as a residue (NiO). For Fe(III) complex which followed by a major decomposition of the organic framework between 300\u0026ndash;600\u0026deg;C. final residue matched Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (29.1%), consistent with magnetite formation at high temperature. The close match between observed and calculated weight losses confirmed the proposed compositions [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Complexation with metal ions enhanced the thermal stability of the ligand, particularly delaying major decomposition beyond 300 ℃, suggesting strong coordination and potential for high-temperature applications.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.6. PXRD (Powder X-ray Diffraction)\u003c/h2\u003e\u003cp\u003eThe crystalline nature of the complexes was confirmed by PXRD analysis. Crystalline sizes estimated using by the Scherrer equation ranged from 27.4 to 50.7 nm, placing them in the nanocrystalline regime [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Such nanoscale crystallinity is of interest since it can significantly influence both the catalytic and biological properties of metal complexes, enhancing their reactivity and antimicrobial potential. The crystallite sizes of the ligand and its metal complexes were estimated using the Scherrer equation, and the results are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The free Schiff base ligand exhibited a crystallite size of 44.4 nm which confirming its nanocrystalline nature. Upon coordination with transition metal ions, significant variations in crystallite size were observed. The Co(II) (32.8) and Cu(II) (27.4) complexes displayed reduced crystallite sizes in comparison to the ligand, indicating that metal coordination causes lattice strain and limits crystallite development. In comparison, the Ni(II) complex (41 nm) displayed a size similar to that of the ligand, suggesting that the incorporation of Ni(II) does not significantly change the dimensions of the crystalline domain. Notably, the Fe(III) complex (50.7 nm) demonstrated the greatest crystallite size, indicating improved crystallinity and superior lattice arrangement in the iron-coordinated system. In general, the sizes of the Schiff base complex crystallites range from 27 to 51 nm, and the noted differences are due to variations in ionic radii, coordination geometry, and the extent of distortion caused by the specific metal ions [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. These results emphasize the impact of metal coordination on the crystalline characteristics of Schiff base complexes, which could subsequently influence their stability and functional attributes\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 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eLigand and its complexes of crystallite size\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\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\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\u003e2θ\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCrystallite size\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLigand, L\u003c/p\u003e\u003cp\u003eC\u003csub\u003e16\u003c/sub\u003eH\u003csub\u003e17\u003c/sub\u003eN\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12.8141 degrees\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e444.37\u0026nbsp;\u0026Aring; (44.44\u0026nbsp;nm)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCobalt\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e29.692 degrees\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e327.74 \u0026Aring; (32.8 nm)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCopper\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15.475 degrees\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e273.97 \u0026Aring; (27.4 nm)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNickle\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12.6746 degrees\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e410 \u0026Aring; (41.0 nm)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIron\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e29.695 degrees\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e507.32 \u0026Aring; (50.7 nm)\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\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e3.7. Antimicrobial Activity\u003c/h2\u003e\u003cp\u003eThe results of the antimicrobial activity showed a distinct improvement with metal complexation when compared to the free ligand tested against \u003cem\u003eEscherichia coli, Staphylococcus aureus, Candida albicans\u003c/em\u003e, and \u003cem\u003eAspergillus niger.\u003c/em\u003e The Co(II) complex exhibited highest activity (20 mm at 80 \u0026micro;l), while the copper showed 13 mm. The free ligand showed weak inhibition (8 mm), while Ni(II) was inactive. Dose-dependent antibacterial activity was observed for the cobalt and copper complexes, whereas the ligand was inactive against \u003cem\u003eS. aureus.\u003c/em\u003e The Cu(II) complex showed remarkable activity (20 mm) against \u003cem\u003eC. albicans\u003c/em\u003e, nearly comparable to the standard drug ketoconazole, while Co(II) was moderately active. Against \u003cem\u003eA. niger\u003c/em\u003e, Cu(II) complex surpassed even the standard drug at higher concentrations (24 mm vs 23 mm), highlighting its strong antifungal potential.\u003c/p\u003e\u003cp\u003eThe enhanced antimicrobial effect of cobalt and copper complexes can be attributed to increased lipophilicity upon chelation, which facilitates penetration of microbial cell membranes [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Additionally, transition metal ions may promote redox reactions inside microbial cells, disrupting DNA or protein functions. The relatively weak activity of the Ni(II) complex suggests that the geometry and electronic properties of the metal center strongly influence biological activity [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\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 6\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eDiameter of inhibition zone (mm) of Schiff base ligand and its complexes against \u003cem\u003eE. coli and S. aureus\u003c/em\u003e bacteria\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"14\"\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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eS. No.\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eSamples\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"6\" nameend=\"c8\" namest=\"c3\"\u003e\u003cp\u003eActivity against \u003cem\u003eE. coli\u003c/em\u003e bacteria\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"6\" nameend=\"c14\" namest=\"c9\"\u003e\u003cp\u003eActivity against \u003cem\u003eS. aureus\u003c/em\u003e bacteria\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"6\" nameend=\"c8\" namest=\"c3\"\u003e\u003cp\u003eDiameter of inhibition zone (mm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"6\" nameend=\"c14\" namest=\"c9\"\u003e\u003cp\u003eDiameter of inhibition zone (mm)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eStandard\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e20 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e40 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e60 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003e80 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003eStandard\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003e20 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003e40 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c12\"\u003e\u003cp\u003e60 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c13\"\u003e\u003cp\u003e80 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"1\" nameend=\"c14\" namest=\"c14\"\u003e\u0026nbsp;\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLigand\u003c/p\u003e\u003cp\u003e(C\u003csub\u003e16\u003c/sub\u003eH\u003csub\u003e17\u003c/sub\u003eN\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c14\" namest=\"c14\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCoL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e33\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\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c14\" namest=\"c14\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCuL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c14\" namest=\"c14\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNiL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c14\" namest=\"c14\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eTable 7 Diameter of inhibition zone (mm) of Schiff base ligand and its complexes against \u003cem\u003eC. albicans and A. niger\u003c/em\u003e fungal\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabb\" border=\"1\"\u003e\u003ccolgroup cols=\"14\"\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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eS. No.\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eSamples\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"6\" nameend=\"c8\" namest=\"c3\"\u003e\u003cp\u003eActivity against \u003cem\u003eC. albicans\u003c/em\u003e fungal\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"6\" nameend=\"c14\" namest=\"c9\"\u003e\u003cp\u003eActivity against \u003cem\u003eA. niger\u003c/em\u003e fungal\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"6\" nameend=\"c8\" namest=\"c3\"\u003e\u003cp\u003eDiameter of inhibition zone (mm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"6\" nameend=\"c14\" namest=\"c9\"\u003e\u003cp\u003eDiameter of inhibition zone (mm)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eStandard\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e20 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e40 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e60 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003e80 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003eStandard\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003e20 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003e40 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c12\"\u003e\u003cp\u003e60 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c13\"\u003e\u003cp\u003e80 \u0026micro;l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"1\" nameend=\"c14\" namest=\"c14\"\u003e\u0026nbsp;\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLigand\u003c/p\u003e\u003cp\u003e(C\u003csub\u003e16\u003c/sub\u003eH\u003csub\u003e17\u003c/sub\u003eN\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c14\" namest=\"c14\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCoL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c14\" namest=\"c14\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCuL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e23\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\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c14\" namest=\"c14\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNiL\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c14\" namest=\"c14\"\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\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eA new Shiff base ligand and its transition metal complexes were successfully synthesized and comprehensively characterized. Spectral and thermal studies confirmed octahedral coordinated, while PXRD indicated nanoscale crystallinity. Antimicrobial evaluation demonstrated that Co(II) and Cu(II) complexes exhibit promising antibacterial and antifungal activity, with Cu(II) showing superior efficacy. These results highlight the potential of Schiff base transition metal complexes as leads for developing novel antimicrobial agent.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAuthor ContributionsShalini Yadav: Conducted the entire research work, including conceptualization, synthesis of the ligand and metal complexes, characterization, data analysis, antimicrobial studies, and manuscript preparation.Dhirendra Yadav: Assisted in conceptualization and provided guidance during data interpretation.Poonam Verma: Supported experimental design and contributed to manuscript review and editing.Vinod Kumar: Supervised the research, provided overall guidance, and reviewed the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e\u003cp\u003eThe authors gratefully acknowledge SMS Medical College, Jaipur, for providing microbial strains and laboratory facilities.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAbu-Dief AM, Mohamed, IMA (2015) A review on versatile applications of transition metal complexes incorporating Schiff bases. J Basic Appl Sci 4(2):119\u0026ndash;133\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEl-Sawaf AK, West DX, El-Saied FA, El-Bahnasawy RM (1998) Synthesis, magnetic and spectral studies of iron (III), cobalt (II, III), nickel (II), copper (II) and zinc (II) complexes of 4\u0026ndash;formylantipyrine N (4)-antipyrinylthiosemicarbazone. Transit Met Chem (5):649\u0026ndash;55\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBuran K (2025) Metal complexes of sulfamethazine/benzoin-based Schiff base ligand: synthesis, characterization, DFT calculations, and antimicrobial activities. Turk J Biol 49(1):118\u0026ndash;126\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEl-Ghamry MA, Elzawawi FM, Abdel Aziz A A, El-Katori EE (2022) New Schiff base ligand and its novel Cr(III), Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes: Spectral investigation, biological applications, and semiconducting properties. Sci Rep 12(1):17942\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRahaman F, Mruthyunjayaswamy BHM (2014) Synthesis, spectral characterization and biological activity studies of transition metal complexes of Schiff base ligand containing indole moiety. J Mol Struct 1073:1\u0026ndash;10\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOjo AS, Mamman S, Ukoha PO (2022) Synthesis, characterization and antimicrobial studies of 3-bromobenzaldehyde nicotinic acid hydrazone and it\u0026rsquo;s Co(II), Cu(II), Mn(II) and Ni(II) complexes. J Applied Physical Sci Int 14(1):1\u0026ndash;9\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAbou-Melha KS (2008) Transition metal complexes of isonicotinic acid (2-hydroxybenzylidene) hydrazide. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 70(1):162\u0026ndash;70\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAl-Fakeh MS, Alsikhan MA, Alnawmasi JS (2023) Physico-chemical study of Mn (II), Co (II), Cu (II), Cr (III), and Pd (II) complexes with schiff-base and aminopyrimidyl derivatives and anti-cancer, antioxidant, antimicrobial applications. Molecules 28(6):2555\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRajeshwar R, Rajesh RK, Manoj K, Rai BK (2014) Synthesis and characterization of Cu(II), Ni(II), and Co(II) coordination compounds with nitrogen and oxygen containing Schiff base. Orient J Chem 30(1):355\u0026ndash;359\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eQurban S (2011) Synthesis and characterization of some transition metal complexes of Schiff base derived from isonicotinic hydrazide and O-vanillin. Diyala J Pure Sci 7(2):94\u0026ndash;104\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAfsan F, Dalia S, Hossain S, Sarker S, Zahan MK (2018) Synthesis, spectral and thermal characterization of selected metal complexes containing schiff base ligands with antimicrobial activities. Asian J Chem Sci 4(3):1\u0026ndash;9\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRaczuk E, Dmochowska B, Samaszko-Fiertek J, Madaj J (2022) Different Schiff bases\u0026mdash;structure, importance and classification. Molecules 27(3):787\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEl-Mossalamy EH, Al-Harby NF, Aal SA, Ali NM, El-Desawy M, Elewa MM, El Batouti M (2024) Tenability on Schiff base hydrazone derivatives and frontier molecular orbital. Heliyon 10(2):24472\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCiolan F, Patron LU, Marutescu L, Chifiriuc MC (2015) Synthesis, characterization and biological activity of Cu (II), Ni (II), Co (II) and Mn (II) binuclear complexes derived from 1, 3-bis (2\u0026rsquo;-formylphenyl)-1, 3-dioxapropane and L-tryptophan. Farmacia 63:86\u0026ndash;92\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEberendu KO, Eze VC, Ejezie MU, Emele CH, Ogbede BU (2025) Synthesis, spectroscopic characterization, and structural. Synthesis 62(04):106\u0026ndash;119\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKeskioglu E, Gunduzalp AB, \u0026Ccedil;ete S, Hamurcu F, Erk B (2008) Cr (III), Fe (III) and Co (III) complexes of tetradentate (ONNO) Schiff base ligands: synthesis, characterization, properties and biological activity. Spectrochim Acta A Mol Biomol Spectrosc 70(3):634\u0026ndash;40\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eReddy V, Patil N, Reddy T, Angadi SD (2008) Synthesis, characterization and biological activities of Cu (II), Co (II), Ni (II), Mn (II) and Fe (III) complexes with Schiff base derived from 3-(4‐Chlorophenoxymethyl)‐4‐amino‐5‐mercapto‐1, 2, 4‐triazole. J Chem 5(3):529\u0026ndash;38\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBhaskar RS, Ladole CA, Salunkhe NG, Barabde JM, Aswar AS (2020) Synthesis, characterization and antimicrobial studies of novel ONO donor hydrazone Schiff base complexes with some divalent metal (II) ions. Arab J Chem 13(8):6559\u0026ndash;67\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSharma B, Shukla S, Rattan R, Fatima M, Goel M, Bhat M, Dutta S, Ranjan RK, Sharma M (2022) Antimicrobial agents based on metal complexes: present situation and future prospects. Int J Biomater (1):681908\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eIacopetta D, Ceramella J, Catalano A, Mariconda A, Giuzio F, Saturnino C, Longo P, Sinicropi MS (2023) Metal complexes with Schiff bases as antimicrobials and catalysts. Inorganics 11(8):320\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Schiff base, Transition metal complexes, Spectral characterization, Thermal stability, Antimicrobic activity","lastPublishedDoi":"10.21203/rs.3.rs-7945567/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7945567/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA novel Schiff base ligand, isonicotinic acid [1-(3,4-dimethoxyphenyl) ethylidene] hydrazide (INADPEH), was synthesized from condensation of isonicotinic acid hydrazide with 1-(3,4-dimethoxyphenyl)ethan-1-one. The Schiff base and its metal (Cobalt, Copper, Nickle, and Iron) complexes were characterized by elemental analysis, molar conductivity, magnetic moment values, UV-Vis, FTIR, and thermogravimetric analysis (TGA), and were obtained in good yields. The structure of the ligand was also confirmed by \u003csup\u003e1\u003c/sup\u003eH NMR spectroscopy. Analytical and spectral data confirmed that INADPEH acts as a bidentate ligand, coordinating through the azomethine nitrogen and carbonyl oxygen. FTIR and UV-Vis spectra and magnetic susceptibility values collectively suggested predominantly octahedral geometries for the complexes. Thermal studies indicated stepwise decomposition of the complexes, with metal oxides as final residues. The antimicrobial activities of the compounds were tested against \u003cem\u003eEscherichia coli, Staphylococcus aureus, Candida albicans\u003c/em\u003e, and \u003cem\u003eAspergillus niger.\u003c/em\u003e The antibacterial activity results revealed that the free ligand showed lower activity compared to the cobalt and copper complexes, with the copper complex exhibiting highest potency, surpassing the standard in some cases. This study highlights the enhanced biological efficacy arising from the significant role of metal complexation and recommends the potential applications of these hydrazone metal complexes as antimicrobial agents.\u003c/p\u003e","manuscriptTitle":"Synthesis, Spectroscopic Characterization, Thermal Behavior, and Antimicrobial and its Evaluation of Schiff Base Transition Metal Complexes Derived from Isonicotinic Acid Hydrazide","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-04 10:23:45","doi":"10.21203/rs.3.rs-7945567/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"582311d4-a04d-4628-8a80-2e141eb8f230","owner":[],"postedDate":"November 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-11-05T09:53:58+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-04 10:23:45","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7945567","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7945567","identity":"rs-7945567","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}