Designing Functional Metal Complexes via a Schiff base From Disalicylaldehyde and Picolinohydrazide

Designing Functional Metal Complexes via a Schiff base From Disalicylaldehyde and Picolinohydrazide | 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 Designing Functional Metal Complexes via a Schiff base From Disalicylaldehyde and Picolinohydrazide Asmit Patel, Anjali Dixit This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8046362/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 Novel Schiff base ligand, N',N"-(1E,1'E)-(Methylenebis(6-hydroxy-3,1 phenylene))bis(methaneylylidene)di(picolinohydrazide), was successfully synthesized via a two-step procedure. The first step involved the acid-catalyzed condensation of salicylaldehyde with trioxane to form the precursor, 5,5'-methylenebis(2-hydroxybenzaldehyde). This dialdehyde was subsequently condensed with 2-picolinohydrazide in ethanol to yield the final bis-hydrazone Schiff base ligand. The structural identity of both the intermediate and the final ligand was confirmed using Fourier Transform Infrared (FT-IR) and Proton Nuclear Magnetic Resonance 1 H-NMR) spectroscopy. The successful synthesis of this versatile ligand opens avenues for further exploration of its coordination chemistry and its potential applications in areas such as catalysis, chemical sensing, and biological activity. Schiff Base Disalicylaldehyde Picolinohydrazide Synthesis Characterization NMR FT-IR Figures Figure 1 Figure 2 Introduction A key component of contemporary coordination chemistry are schiff bases, which are defined by the presence of a carbon-nitrogen double bond (C = N), also referred to as an imine or azomethine functional group. These compounds, which were first described by Hugo Schiff in 1864, are made by a simple condensation reaction between a primary amine and a carbonyl compound (either ketone or aldehyde) [ 1 ]. Their crucial role in a variety of scientific fields, such as medicinal chemistry, materials science, and catalysis, has been solidified by their synthetic simplicity, exceptional structural versatility, and varied coordination abilities [ 2 , 3 ]. Schiff bases and their metal complexes have a particularly deep biological significance. Their activity depends on the imine linkage, which frequently acts as a pharmacophore. These substances have a wide range of biological characteristics, such as antibacterial, antioxidant, anti-inflammatory, anti-cancer, and anti-Alzheimer effects [ 4 ]. The emergence of multi-drug-resistant pathogens has intensified the search for new antimicrobial agents, and Schiff base metal complexes have shown promising results in combating such resistant strains [ 5 ]. Furthermore, their ability to interact with key enzymes and receptors in the body positions them as potential leads for developing novel therapeutics for diabetes, malaria, and neurodegenerative disorders [ 6 ].Further, several salicylaldehyde-derived Schiff base complexes have demonstrated notable antimicrobial and antioxidant activities [ 7 ]. Schiff bases are finding use in advanced materials science in addition to biology. Their strong light-harvesting capabilities, tunable electronic characteristics, and high thermal stability make photovoltaics appealing. Because of their effective charge transfer and luminescent qualities, schiff bases and their complexes are being investigated as sensitizers in dye-sensitized solar cells (DSSCs) and as possible constituents in organic light-emitting diodes (OLEDs) [ 8 , 9 ]. The HOMO-LUMO gap, a crucial parameter for maximizing the efficiency of solar energy conversion, can be fine-tuned thanks to their distinct molecular structure [ 10 ]. Schiff bases are also useful in catalysis, where they act as strong ligands for a range of metal-catalyzed reactions, such as C-C coupling reactions, oxidation, and epoxidation [ 11 ]. Schiff bases are highly valued chemosensors for biological and environmental monitoring in the field of chemical sensing because of their "off-on" fluorescent responses when they bind with particular metal ions or small molecules [ 12 ]. Their luminescent [ 13 ] and magnetic [ 14 ] properties are also exploited in developing new molecular devices and single-molecule magnets (SMMs). The class of compartmental Schiff base ligands is one that is especially fascinating. These complex ligands can bind several metal ions at once because they are made with two or more different coordination pockets close together. Synergistic effects between various metal centers can result in enhanced catalytic activity, distinct magnetic behavior, or novel reactivity not observed in monometallic systems, making this architecture perfect for the creation of heterometallic complexes [ 15 ]. Condensing a polycarbonyl precursor with a polyamine to produce distinct cavities of different sizes and donor atom sets is a common step in the synthesis of such ligands [ 16 ]. Recent work on 3d–4f heterometallic Schiff base complexes highlights their unique magnetic and electronic properties [ 17 ]. One essential building block for compartmental ligand construction is the dialdehyde 5,5'-methylenebis(2-hydroxybenzaldehyde). Its structure, featuring two salicylaldehyde motifs connected by a methylene spacer, creates proximate binding pockets suitable for metal coordination. Ligands synthesized from this precursor have shown significant utility, functioning as catalysts in the oxidation of alcohols [ 18 ] and as selective fluorescent probes for ions like Al³⁺ [ 19 ]. Enhancing its coordinative versatility, the introduction of a hydrazide moiety, such as picolinohydrazide, is particularly effective. This group provides additional N- and O-donor atoms, enabling the formation of stable five- or six-membered chelate rings with metal ions, which often improves complex stability and can yield novel functional properties. This work describes the rational design, synthesis, and complete structural characterization of a novel compartmental Schiff base ligand, N',N"-(1E,1'E)-(Methylenebis(6-hydroxy-3,1-phenylene))bis(methaneylylidene)di(picolinohydrazide), in light of the well-established significance of disalicylaldehyde-based scaffolds and the improved coordinative potential of picolinohydrazide. This multi-dentate ligand's successful synthesis provides the necessary foundation for further research into its coordination chemistry with different transition and lanthanide metal ions, as well as the investigation of the possible uses of the resulting complexes in biomimetic, catalysis, and sensing studies. Material and Methods Salicylaldehyde, trioxane, glacial acetic acid, concentrated sulfuric acid, 2-picolinohydrazide, and ethanol were all analytical-grade chemicals that were used exactly as supplied. A suitable NMR spectrometer was used to record the H-NMR spectra, and a standard FT-IR spectrophotometer was used to obtain the FT-IR spectra. Step 1: Synthesis of 5,5'-methylenebis(2-hydroxybenzaldehyde) A solution of salicylaldehyde (7 mL, 0.065 mol) in glacial acetic acid (5 mL) was prepared. Trioxane (1.8 mg, 0.002 mol) was dissolved into this solution. A mixture of concentrated H 2 SO 4 (50 µL) and glacial acetic acid (250 µL) was added slowly with stirring under a nitrogen atmosphere at 90°C. The reaction mixture was maintained at this temperature with stirring for 24 hours. It was then poured into ice-cold water and allowed to stand overnight. The resulting precipitate was filtered, washed with distilled water (3 × 2 mL), and dried. The crude product was dissolved in acetone and crystallized via slow evaporation to yield a white crystalline compound. Step 2: Synthesis of the Schiff Base Ligand A mixture of 5,5'-methylenebis(2-hydroxybenzaldehyde) (0.2 mmol) and 2-picolinohydrazide (0.5 mmol) was dissolved in hot ethanol (8 mL) at 80°C. Three to four drops of glacial acetic acid were added, and the resultant mixture was refluxed overnight at 80°C. Upon cooling, the precipitate formed was filtered, washed with ethanol, and dried, yielding the title ligand as a solid in 68% yield. Result and Discussion Synthesis As shown in Scheme 1 , the target Schiff base ligand was synthesized in two high-yielding steps. To create the final bis-hydrazone ligand, the key dialdehyde intermediate from the first step underwent a double condensation with 2-picolinohydrazide. The imine formation was effectively aided by the use of glacial acetic acid as a catalyst. FT-IR Analysis The carbonyl (C=O) stretch of the aldehyde group is represented by a distinctive sharp band at about 1680 cm -1 in the FT-IR spectrum of the intermediate, 5,5'-methylenebis(2-hydroxybenzaldehyde) ( Figure 1a ). The phenolic O-H stretch was identified as the source of a broadin the 3200–3500 cm -1 range. The formation of the C=N (imine) bond was confirmed by the appearance of new bands around 1620-1650 cm -1 and the disappearance of the characteristic aldehyde C=O stretch in the final Schiff base ligand's FT-IR spectrum ( Figure 1b ). The suggested structure was further confirmed by the presence of bands corresponding to N-H stretches and amide C=O (from the hydrazide moiety). 1 H-NMR Spectroscopy The 1 H-NMR spectrum of the dialdehyde intermediate ( Figure 2a ) exhibited a characteristic singlet around 10 ppm for the aldehyde proton (-CHO) and a singlet around 4.0 ppm for the methylene bridge (-CH 2 -). The aromatic and phenolic protons appeared in the expected regions. The 1 H-NMR spectrum of the final ligand ( Figure 2b ) showed the definitive disappearance of the aldehyde proton signal. The appearance of a new singlet around 8.5 ppm, assigned to the imine proton (-CH=N-), provided conclusive evidence for the successful formation of the Schiff base [20].Comparable spectral features have been observed in other hydrazone-based Schiff base systems [21].The methylene bridge proton signal remained, and the complex set of signals in the aromatic region integrated correctly for the entire molecular framework. Conclusion By using spectroscopic methods, a new disalicylaldehyde-based Schiff base ligand was successfully created and described. The structural validation ofthe two-step synthetic route was performed using FT-IR and H-NMR spectroscopy. This newly developed ligand, with multiple donor atoms (N and O), is an excellent candidate for forming stable complexes with various metal ions. Its potential applications are vast, spanning biological activity, catalysis, and chemical sensing. Future work will focus on synthesizing and characterizing metal complexes (e.g., with V, Cu, and Ln ions) and evaluating their efficacy in the aforementioned applications, particularly in combating antibiotic resistance and developing new catalytic systems. Declarations Acknowledgements I extend my sincere gratitude to my lab-mates at BBAU, and my family for their unwavering support and guidance throughout this research. Ethical approval: Not applicable. Consent to participate: Not applicable. Consent to publish : Not applicable. Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author Contributions Asmit Patel : Conceptualization, Methodology, Writing – Original Draft, Formal Analysis, Validation. Anjali Dixit : Investigation, Synthesis, Purification. Data Availability Data sharing is not applicable to this article as no datasets were generated or analysed during the current study. References Schiff, H. Mittheilungenausdemuniversitätslaboratorium in Pisa: eineneuereiheorganischerbasen. Ann. Chem. Pharm . 1864, 131 , 118–119. Patai, S. The Chemistry of the Carbon–Nitrogen Double Bond. Wiley, London, 1970. Calligaris, M.; Randaccio, L. (Eds.). Structures and Bonding in Schiff Base Complexes. Springer-Verlag, Berlin, 1982 Sinicropi, M.S.; Ceramella, J.; Iacopetta, D.; Catalano, A.; Mariconda, A.; Rosano, C.; Saturnino, C.; El-Kashef, H.; Longo, P. Metal Complexes with Schiff Bases: Data Collection and Recent Studies on Biological Activities. Int. J. Mol. Sci . 2022, 23 , 14840. https://doi.org/10.3390/ijms232314840 Al-Amiery, A.A.; Al-Majedy, Y.K.; Ibrahim, H.H.; Al-Tamimi, A.A. 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Acta Part A 2010, 75, 102–109. https://doi.org/10.1016/j.saa.2009.10.005 Scheme Scheme 1 and 2 are available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files scheme1and2.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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1","display":"","copyAsset":false,"role":"figure","size":356277,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003eFT-IR Spectrum of N, N-(1E, 1E’)- (Methylenebis(6-hydroxy-3,1-phenylene)bis(methaneylydene)di(picolinohydrazide)\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eb \u003c/strong\u003eFT-IR Spectrum of 5, 5’-methylenebis (2-hydroxybenzaldehyde)\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8046362/v1/72224a096c704dc82d544c8e.png"},{"id":96911166,"identity":"d9ff29d0-a8aa-41c6-a9ec-160e52454066","added_by":"auto","created_at":"2025-11-27 13:21:30","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":222006,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e\u003csup\u003e1\u003c/sup\u003eH-NMR of 5,5’-methylenebis (2-hydroxybenzaldehyde)\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eb\u003c/strong\u003e\u003csup\u003e1\u003c/sup\u003eH-NMR OF N’,N”-(1E,1E’)-(Methylenebis(6-hydroxy-3,1-phenylene)bis(methaneylydene)di(picolinohydrazide)\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8046362/v1/464a1e74d5b158074a2ee880.png"},{"id":101193828,"identity":"f95bc57b-efc1-47d0-8e82-c75d772329be","added_by":"auto","created_at":"2026-01-27 07:43:06","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":987149,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8046362/v1/b48c3025-3b23-4dd3-98cb-434dc041fa7f.pdf"},{"id":96911171,"identity":"33b6507c-ff92-499b-9ba0-d1aba62d9a6a","added_by":"auto","created_at":"2025-11-27 13:21:30","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":160369,"visible":true,"origin":"","legend":"","description":"","filename":"scheme1and2.docx","url":"https://assets-eu.researchsquare.com/files/rs-8046362/v1/416b46bc6bd5f9d64f72ec80.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Designing Functional Metal Complexes via a Schiff base From Disalicylaldehyde and Picolinohydrazide","fulltext":[{"header":"Introduction","content":"\u003cp\u003eA key component of contemporary coordination chemistry are schiff bases, which are defined by the presence of a carbon-nitrogen double bond (C\u0026thinsp;=\u0026thinsp;N), also referred to as an imine or azomethine functional group. These compounds, which were first described by Hugo Schiff in 1864, are made by a simple condensation reaction between a primary amine and a carbonyl compound (either ketone or aldehyde) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Their crucial role in a variety of scientific fields, such as medicinal chemistry, materials science, and catalysis, has been solidified by their synthetic simplicity, exceptional structural versatility, and varied coordination abilities [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eSchiff bases and their metal complexes have a particularly deep biological significance. Their activity depends on the imine linkage, which frequently acts as a pharmacophore. These substances have a wide range of biological characteristics, such as antibacterial, antioxidant, anti-inflammatory, anti-cancer, and anti-Alzheimer effects [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. The emergence of multi-drug-resistant pathogens has intensified the search for new antimicrobial agents, and Schiff base metal complexes have shown promising results in combating such resistant strains [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Furthermore, their ability to interact with key enzymes and receptors in the body positions them as potential leads for developing novel therapeutics for diabetes, malaria, and neurodegenerative disorders [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].Further, several salicylaldehyde-derived Schiff base complexes have demonstrated notable antimicrobial and antioxidant activities [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eSchiff bases are finding use in advanced materials science in addition to biology. Their strong light-harvesting capabilities, tunable electronic characteristics, and high thermal stability make photovoltaics appealing. Because of their effective charge transfer and luminescent qualities, schiff bases and their complexes are being investigated as sensitizers in dye-sensitized solar cells (DSSCs) and as possible constituents in organic light-emitting diodes (OLEDs) [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The HOMO-LUMO gap, a crucial parameter for maximizing the efficiency of solar energy conversion, can be fine-tuned thanks to their distinct molecular structure [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eSchiff bases are also useful in catalysis, where they act as strong ligands for a range of metal-catalyzed reactions, such as C-C coupling reactions, oxidation, and epoxidation [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Schiff bases are highly valued chemosensors for biological and environmental monitoring in the field of chemical sensing because of their \"off-on\" fluorescent responses when they bind with particular metal ions or small molecules [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Their luminescent [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] and magnetic [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] properties are also exploited in developing new molecular devices and single-molecule magnets (SMMs).\u003c/p\u003e\u003cp\u003eThe class of compartmental Schiff base ligands is one that is especially fascinating. These complex ligands can bind several metal ions at once because they are made with two or more different coordination pockets close together. Synergistic effects between various metal centers can result in enhanced catalytic activity, distinct magnetic behavior, or novel reactivity not observed in monometallic systems, making this architecture perfect for the creation of heterometallic complexes [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Condensing a polycarbonyl precursor with a polyamine to produce distinct cavities of different sizes and donor atom sets is a common step in the synthesis of such ligands [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Recent work on 3d\u0026ndash;4f heterometallic Schiff base complexes highlights their unique magnetic and electronic properties [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eOne essential building block for compartmental ligand construction is the dialdehyde 5,5'-methylenebis(2-hydroxybenzaldehyde). Its structure, featuring two salicylaldehyde motifs connected by a methylene spacer, creates proximate binding pockets suitable for metal coordination. Ligands synthesized from this precursor have shown significant utility, functioning as catalysts in the oxidation of alcohols [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] and as selective fluorescent probes for ions like Al\u0026sup3;⁺ [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Enhancing its coordinative versatility, the introduction of a hydrazide moiety, such as picolinohydrazide, is particularly effective. This group provides additional N- and O-donor atoms, enabling the formation of stable five- or six-membered chelate rings with metal ions, which often improves complex stability and can yield novel functional properties.\u003c/p\u003e\u003cp\u003eThis work describes the rational design, synthesis, and complete structural characterization of a novel compartmental Schiff base ligand, N',N\"-(1E,1'E)-(Methylenebis(6-hydroxy-3,1-phenylene))bis(methaneylylidene)di(picolinohydrazide), in light of the well-established significance of disalicylaldehyde-based scaffolds and the improved coordinative potential of picolinohydrazide. This multi-dentate ligand's successful synthesis provides the necessary foundation for further research into its coordination chemistry with different transition and lanthanide metal ions, as well as the investigation of the possible uses of the resulting complexes in biomimetic, catalysis, and sensing studies.\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cp\u003eSalicylaldehyde, trioxane, glacial acetic acid, concentrated sulfuric acid, 2-picolinohydrazide, and ethanol were all analytical-grade chemicals that were used exactly as supplied. A suitable NMR spectrometer was used to record the H-NMR spectra, and a standard FT-IR spectrophotometer was used to obtain the FT-IR spectra.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eStep 1: Synthesis of 5,5\u0026apos;-methylenebis(2-hydroxybenzaldehyde)\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA solution of salicylaldehyde (7 mL, 0.065 mol) in glacial acetic acid (5 mL) was prepared. Trioxane (1.8 mg, 0.002 mol) was dissolved into this solution. A mixture of concentrated H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e (50 \u0026micro;L) and glacial acetic acid (250 \u0026micro;L) was added slowly with stirring under a nitrogen atmosphere at 90\u0026deg;C. The reaction mixture was maintained at this temperature with stirring for 24 hours. It was then poured into ice-cold water and allowed to stand overnight. The resulting precipitate was filtered, washed with distilled water (3 \u0026times; 2 mL), and dried. The crude product was dissolved in acetone and crystallized via slow evaporation to yield a white crystalline compound.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eStep 2: Synthesis of the Schiff Base Ligand\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA mixture of 5,5\u0026apos;-methylenebis(2-hydroxybenzaldehyde) (0.2 mmol) and 2-picolinohydrazide (0.5 mmol) was dissolved in hot ethanol (8 mL) at 80\u0026deg;C. Three to four drops of glacial acetic acid were added, and the resultant mixture was refluxed overnight at 80\u0026deg;C. Upon cooling, the precipitate formed was filtered, washed with ethanol, and dried, yielding the title ligand as a solid in 68% yield.\u003c/p\u003e"},{"header":"Result and Discussion","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eSynthesis\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAs shown in \u003cstrong\u003eScheme 1\u003c/strong\u003e, the target Schiff base ligand was synthesized in two high-yielding steps. To create the final bis-hydrazone ligand, the key dialdehyde intermediate from the first step underwent a double condensation with 2-picolinohydrazide. The imine formation was effectively aided by the use of glacial acetic acid as a catalyst.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFT-IR Analysis\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe carbonyl (C=O) stretch of the aldehyde group is represented by a distinctive sharp band at about 1680 cm\u003csup\u003e-1\u003c/sup\u003e in the FT-IR spectrum of the intermediate, 5,5\u0026apos;-methylenebis(2-hydroxybenzaldehyde) (\u003cstrong\u003eFigure 1a\u003c/strong\u003e). The phenolic O-H stretch was identified as the source of a broadin the 3200\u0026ndash;3500 cm\u003csup\u003e-1\u003c/sup\u003e range. The formation of the C=N (imine) bond was confirmed by the appearance of new bands around 1620-1650 cm\u003csup\u003e-1\u003c/sup\u003e and the disappearance of the characteristic aldehyde C=O stretch in the final Schiff base ligand\u0026apos;s FT-IR spectrum (\u003cstrong\u003eFigure 1b\u003c/strong\u003e). The suggested structure was further confirmed by the presence of bands corresponding to N-H stretches and amide C=O (from the hydrazide moiety).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e\u003csup\u003e1\u003c/sup\u003e\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eH-NMR Spectroscopy\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe \u003csup\u003e1\u003c/sup\u003eH-NMR spectrum of the dialdehyde intermediate (\u003cstrong\u003eFigure 2a\u003c/strong\u003e) exhibited a characteristic singlet around 10 ppm for the aldehyde proton (-CHO) and a singlet around 4.0 ppm for the methylene bridge (-CH\u003csub\u003e2\u003c/sub\u003e-). The aromatic and phenolic protons appeared in the expected regions.\u003c/p\u003e\n\u003cp\u003eThe \u003csup\u003e1\u003c/sup\u003eH-NMR spectrum of the final ligand (\u003cstrong\u003eFigure 2b\u003c/strong\u003e) showed the definitive disappearance of the aldehyde proton signal. The appearance of a new singlet around 8.5 ppm, assigned to the imine proton (-CH=N-), provided conclusive evidence for the successful formation of the Schiff base [20].Comparable spectral features have been observed in other hydrazone-based Schiff base systems [21].The methylene bridge proton signal remained, and the complex set of signals in the aromatic region integrated correctly for the entire molecular framework.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eBy using spectroscopic methods, a new disalicylaldehyde-based Schiff base ligand was successfully created and described. The structural validation ofthe two-step synthetic route was performed using FT-IR and H-NMR spectroscopy. This newly developed ligand, with multiple donor atoms (N and O), is an excellent candidate for forming stable complexes with various metal ions. Its potential applications are vast, spanning biological activity, catalysis, and chemical sensing. Future work will focus on synthesizing and characterizing metal complexes (e.g., with V, Cu, and Ln ions) and evaluating their efficacy in the aforementioned applications, particularly in combating antibiotic resistance and developing new catalytic systems.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eI extend my sincere gratitude to my lab-mates at BBAU, and my family for their unwavering support and guidance throughout this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eEthical approval:\u0026nbsp;\u003c/em\u003e\u003c/strong\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eConsent to participate:\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eConsent to publish\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interest\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAsmit Patel\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e Conceptualization, Methodology, Writing \u0026ndash; Original Draft, Formal Analysis, Validation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAnjali Dixit\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e Investigation, Synthesis, Purification.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData sharing is not applicable to this article as no datasets were generated or analysed during the current study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eSchiff, H. 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The role of 3d-4f exchange interaction in SMM behavior and magnetic refrigeration of carbonato bridged\u0026hellip; (Ln = Dy, Tb and Gd) complexes of an unsymmetrical N\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003edonor ligand. \u003cem\u003eDalton Trans\u003c/em\u003e. 2019, \u003cstrong\u003e48\u003c/strong\u003e, 15170\u0026ndash;15183. https://doi.org/10.1039/C9DT03022E\u003c/li\u003e\n\u003cli\u003eNaskar, S.; Mondal, A.; Konar, S. 3d\u0026ndash;4f heterometallic Schiff base complexes: synthesis, structures, and magnetic properties. \u003cem\u003eDalton Trans.\u003c/em\u003e 2022, 51, 4020\u0026ndash;4032. https://doi.org/10.1039/D1DT04233F\u003c/li\u003e\n\u003cli\u003eKachhap, P.; Chaudhary, N.; Haldar, C. Catalytic Oxidation of Aliphatic Alcohol by Graphene Oxide Supported Binuclear Dioxidovanadium(V) Complexes. \u003cem\u003eJ. Chem. 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Acta Part A\u003c/em\u003e 2010, 75, 102\u0026ndash;109. https://doi.org/10.1016/j.saa.2009.10.005\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Scheme","content":"\u003cp\u003eScheme 1 and 2 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"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, Disalicylaldehyde, Picolinohydrazide, Synthesis, Characterization, NMR, FT-IR","lastPublishedDoi":"10.21203/rs.3.rs-8046362/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8046362/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eNovel Schiff base ligand, N',N\"-(1E,1'E)-(Methylenebis(6-hydroxy-3,1 phenylene))bis(methaneylylidene)di(picolinohydrazide), was successfully synthesized via a two-step procedure. The first step involved the acid-catalyzed condensation of salicylaldehyde with trioxane to form the precursor, 5,5'-methylenebis(2-hydroxybenzaldehyde). This dialdehyde was subsequently condensed with 2-picolinohydrazide in ethanol to yield the final bis-hydrazone Schiff base ligand. The structural identity of both the intermediate and the final ligand was confirmed using Fourier Transform Infrared (FT-IR) and Proton Nuclear Magnetic Resonance \u003csup\u003e1\u003c/sup\u003eH-NMR) spectroscopy. The successful synthesis of this versatile ligand opens avenues for further exploration of its coordination chemistry and its potential applications in areas such as catalysis, chemical sensing, and biological activity.\u003c/p\u003e","manuscriptTitle":"Designing Functional Metal Complexes via a Schiff base From Disalicylaldehyde and Picolinohydrazide","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-27 13:21:26","doi":"10.21203/rs.3.rs-8046362/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":"b43bf727-f1f6-4ada-b4bb-6cf9edacdf55","owner":[],"postedDate":"November 27th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-01-27T07:42:09+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-27 13:21:26","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8046362","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8046362","identity":"rs-8046362","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}