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Synthetic and antibacterial studies of schiff base complexes derived from 2,3-diaminopyridine and o-vanillin
Abstract
Two new Schiff bases (1a and 2a) and eight transition metal complexes (1b-1d and 2b-2f) derived from 2,3-diaminopyridine (DAPY) and ortho-vanillin (ValH) have been synthesised and characterised by elemental analyses, magnetic susceptibility measurements, IR and NMR spectra. The Schiff bases and most of the metal complexes display antibacterial activity.
... (Ibrahim et al., 2006). A variety of routes have been used for the synthesis of Schiff bases like reflux reactions (Uddin et al., 2014), stirring at ambient temperature (Umofia et al., 2018;Shipra et al., 2019), microwave irradiation (Venugopala et al., 2008;Bhagat et al., 2013;Shntaif and Rashid, 2016), ultrasonication (Li et al, 2001;Venkatesan et al., 2011;Ahmed et al., 2014), and direct fusion method (Bendale et al., 2011;Abood, 2014;Mahmood and Khudhair, 2017). The conventional method for the synthesis of this compound is the reflux method and this is done in acid or alkaline medium (Qin et al., 2013). ...
The Schiff base was acquired from the reaction between 4-ethoxyaniline and 2-pyridinecarboxaldehyde using three (3) synthetic methods: 2 hours reflux in ethanol, stirring in ethanol and in an ethanol-water (1:1 v/v) mixture at ambient temperature for an hour. The synthesis of 4-ethoxyaniline-2-pyridinecarboxaldehyde Schiff base afforded dark-brown crystals with a melting point of 118-120°C. The reflux reaction in ethanol gave the highest yield of 83.5% while the reaction in ethanol and in ethanol-water (1:1 v/v) mixture at ambient temperature gave 73.0% and 43.6% yield respectively. The confirmation for the formation of a new aliphatic C=N functional group was given by the IR spectrum that showed a band at 1625cm-1 for an aliphatic C=N group; the 13C NMR spectrum that showed the presence of the imino carbon (C=N) at chemical shift 158.48ppm while the 1H NMR spectral data δ(ppm) for the compound gave a one proton singlet (HC=N-) at 8.69. The spectral data were in correlation with the predicted structure of the Schiff base.
... In the recent years, chemists have been paid much attention to the chemistry of the metal complexes of Schiff bases containing nitrogen and other donor atoms [2][3][4][5]. Most of the Schiff bases and their complexes have been found to possess important biological and catalytic activity [6,7]. Furthermore, Biochemists are now paying their active attention to the chemotherapeutic Schiff bases [8,9]. ...
Schiff bases and their complexes are playing very important role in medicinal chemistry from ancient period because of their broad range of biological activities such as antibacterial, antifungal, antimalarial and antiviral etc. In this research project several Schiff bases have been synthesized from p-toluidine and derivatives of benzaldehyde to investigate the antibacterial activity. The synthesized Schiff bases have been characterized by IR and 1 H-NMR spectral analysis. All the synthesized compounds have been screened for their in vitro antibacterial activity against gram (+) and gram (-) bacterial strains by disc diffusion method. Among the synthesized compounds, the compound 5 showed strong efficacy against E. coli and the others showed moderate activity against bacterial strains.
... albicans. The complexes are more active than the parent ligand because the metal complex may serve as a vehicle for activation of ligand as the principle cytotoxic species [35]. It is known that chelating tends to make the metal complex acts as more powerful and potent bactericidal agents, thus killing more of the bacteria than the ligand [36]. ...
In this study, Metal (II) Complexes of Mn (II), Fe (III), Co (II) and Ni (II) with Schiff base ligand derived from Trimethoprim and Cyclohexanone were synthesized and characterized using various physic-chemical techniques such as solubility, conductivity, melting point determination, UV/Vis and Fourier transform infrared, 1H-NMR and elemental analysis. On the basis of these characterizations, a six coordinated octahedral geometry has been proposed for all the complexes. The Schiff base ligand and its complexes were screened for their antimicrobial activity against some pathogenic microbial isolate and compared with the parent drug. The antimicrobial activity results showed the following trend: metal complexes > Schiff base ligands > Parent drugs. This suggest potential antimicrobials agents with broad spectrum activity. Computational studies further revealed that M-Cl bond is responsible for the trend in antimicrobial properties among the complexes.
Keywords:Bacterial Resistance; Bacteria; Trimethoprim; Schiff Base; Complexes
... Metal complexes of Fe (II), Co (II), Ni(II), Cu(II), Zn(II) or Cd (II) with Schiff base N-(2-thienylmethylidene)-2-aminopyridine have been studied (13). Synthesis and antibacterial activity of Schiff bases and transition metal complexes derived from 2, 3diminopyridine and o-vanillin has been study (14). Synthesis and antimicrobial activity of new metal [Mg(II), Fe(II), Co(II), Ni(II), Zn(II) and Cd(II)] complexes from 2-(1'/2'-hydroxynaphthyl) benzoxazoles was studied (15). ...
Novel Schiff bases (E)-6-(benzylideneamino)-3,3-dimethyl-7-oxo-4-thia-1-aza-bicyclo heptane-2-carboxylic acid (L1) and (E)-6-(4-hydroxy benzylideneamino)-3,3-dimethyl-7-oxo-4-thia-1-aza-bicyclo heptane-2-carboxylic acid (L2) were synthesized. Further metal complexes of these Schiff bases were synthesized using various metal nitrates. Both Schiff bases and their metal complexes were screened for antibacterial activity against different bacterial species such as Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. Some Schiff base and metal complexes showed moderate to excellent activity.
... Metal complexes of Fe (II), Co (II), Ni(II), Cu(II), Zn(II) or Cd (II) with Schiff base like N-(2-thienylmethylidene)-2-aminopyridine have been studied by Spinu et al [6]. Synthesis and antibacterial activity of schiff bases and transition metal complexes derived from 2, 3diminopyridine and ortho-vanillin has been studied by Henri et al. [7]. Anil Kumar et al. [8] described the synthesis and antimicrobial activity of new metal [Mg(II), Fe(II), Co(II), Ni(II), Zn(II) and Cd(II)] complexes from 2-(1'/2'-hydroxynaphthyl) benzoxazoles. ...
... The mono-and bis-Schiff bases of o-vanillin and 2,3diaminopyridine have been used as ionophores in a Cu(II) selective electrochemical sensor [5]. These compounds as well as their metal complexes have been found to possess biological activity [6]. Antibacterial activity has also been reported for the ruthenium(II) complex of the Schiff base of o-vanillin and 2-aminopyridine [7]. ...
Two new series of copper(II) and nickel(II) complexes with two new Schiff base ligands 2-((2,4-dimethylphenylimino)methyl)-6-methoxy-4-nitrophenol and 2-((3,4-difluorophenylimino)methyl)-6-methoxy-4-nitrophenol have been prepared. The Schiff base ligands were synthesized by the condensation of 2-hydroxy-3-methoxy-5-nitrobenzaldehyde with 2,4-dimethylaniline or 3,4-difluoroaniline. The ligands and their metal complexes have been characterized by IR, 1H NMR, mass and electronic spectra and TG analysis. The Schiff base ligands and their metal complexes were tested for antimicrobial activity against Gram positive bacteria Staphylococcus aureus, and Streptococcus pyogenes and Gram negative bacteria Escherichia coli, and Pseudomonas aeruginosa and fungus Candida albicans, Aspergillus niger, and Aspergillus clavatus using Broth Dilution Method.
... of metals in Schiff base in the form of metal complexes exhibited some degree of biological activities like antifungal [5], antibacterial [6], anticancer [7], and anti-inflammatory activity [8]. As p-CBA used as an important reaction intermediate, its rate of reaction plays a crucial role. ...
p-Chlorobenzaldehyde (p-CBA) is used as an important chemical intermediate for the preparation of pharmaceuticals, agricultural chemicals, dyestuffs, optical brighteners, and metal finishing products. The study aimed to evaluate the effect of biofield energy treatment on the physicochemical and spectroscopic properties of p-CBA. The study was accomplished in two groups i.e. control and treated. The control group was remained as untreated, while the treated group was subjected to Mr. Trivedi’s biofield energy treatment. Finally, both the samples (control and treated) were evaluated using various analytical techniques. The surface area analysis showed a substantial increase in the surface area by 23.06% after biofield treatment with respect to the control sample. The XRD analysis showed the crystalline nature of both control and treated samples. The X-ray diffractogram showed the significant alteration in the peak intensity in treated sample as compared to the control. The XRD analysis showed the slight increase (2.31%) in the crystallite size of treated sample as compared to the control. The TGA analysis exhibited the decrease (10%) in onset temperature of thermal degradation form 140°C (control) to 126°C in treated sample. The Tmax (maximum thermal degradation temperature) was slightly decreased (2.14%) from 157.09°C (control) to 153.73°C in treated sample of p-CBA. This decrease in Tmax was possibly due to early phase of vaporization in treated sample as compared to the control. The FT-IR spectrum of treated p-CBA showed the increase in wavenumber of C=C stretching as compared to the control. The UV spectroscopic study showed the similar pattern of wavelength in control and treated samples.
Altogether, the surface area, XRD, TGA-DTG and FT-IR analysis suggest that Mr. Trivedi’s biofield energy treatment has the impact to alter the physicochemical properties of p-CBA. This treated p-CBA could be utilized as a better chemical intermediate than the control p-CBA for the synthesis of pharmaceutical drugs and organic chemicals.
Schiff bases are considered as valuable compounds because of their versatility in the field of medicine and pharmaceuticals. A new Schiff base was formed by condensation of 4-dimethylaminobenzaldehyde with benzamide in 1:1 M ratio. The catalytic activity of Schiff base is raised by making its complex with metals. Different transition metals (Ni, Co, Zn, Pb) were used to form the metal complex with the newly formed Schiff base. Metal complexes of Schiff bases derived from 4-dimethylaminobenzaldehyde was processed for good yield of product. The Schiff bases show strong biological activities that includes antifungal, anticancer, antibacterial activities etc. The complexes of Schiff base metal are in the wide range of study. They have high thermal power and have useful effects in many fields. This effect of metal has increased the biological activities of such compounds and therefore the scientists have changed their behavior towards coordination chemistry. The new complexes were also characterized by using UV, IR, XRD and molar conductive techniques. This article throws light on the formation of 4-dimethylaminobenzaldehyde derivatives of different Schiff base metal complexes, its importance and use of Schiff bases along with its metal complexes. The investigation of antibacterial activities of ligand and complexes were done against bacteria like Staphylococcus Aureus, Bacillus subtilis and Escherichia Coli. It was found that the complexes showed marvelous result as compare to ligand against bacteria.
Abstract
The Schiff base 3-{(E)-[(2-hydroxyphenyl)imino]methyl}benzene-1,2-diol was synthesized by the condensation of 2,3-dihydroxybenzaldehyde and 2-aminophenol in water at room temperature. The crystal was grown using two solvents (dry methanol and 60% methanol). The compound was characterized using elemental microanalysis, IR, NMR, UV spectroscopies and single-crystal X-ray diffraction crystallography. The X-ray structure reveals that the Schiff base crystallizes as a methanol solvate in dry methanol with triclinic crystal system, space group P-1 and Z = 2 in the unit cell and as a non-methanol solvate in 60% methanol with triclinic crystal system, space group P-1 and Z = 4 in the unit cell. The compound showed absorption bands at 272, 389, 473 and 602 nm in DMSO. These bands were assigned as π → π ∗, n → π∗ and n-σ∗ transitions. The 473 and 602 nm bands in DMSO reveal that the compound exists in tautomeric forms. The presence of N-H, C-O and Cdouble bond; length as m-dashN stretching vibrations in the IR spectrum indicates that the compound is zwitterionic in the solid state. This study was supplemented using density functional theory method.
Complexes of Ni(II) and Cu(II) with Schiff bases, vanillidene-4 chloroaniline (VCA) and vanillidene-3-nitroaniline (VNA) have been synthesized and characterized by elemental analysis, molar conductance, magnetic measurement, IR and electronic spectra. Coordination of azomethine nitrogen in the Schiff base of the metal has been proposed. Antimicrobial activities of the complexes have also been evaluated.
Metal chelates of Mo(VI), W(VI) and Cr(III) with Schiff bases have been synthesized by the condensation of o-vanillin with aspartic acid and characterized by spectroscopic method. Coordination of azomethine nitrogen in the Schiff base of the metal has been proposed.
The complexes of Cu(II), Ni(II), Co(II), Mn(II), and Zn(II) with isonicotinoyl-hydrazone -2,4,6-trimethylbenzaldehyde (INHTB) are reported. The complexes have been characterized by analytical data, IR, UV-Vis, NMR spectra, magnetic susceptibility, thermal analysis and for the Cu(II) complex the ESR spectrum has been recorded. The anti-bacterial activity of these complexes were investigated against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella enteritidis, Shigella flexneri bacteria. The INHTB ligand is coordinated at the metallic ions by oxygen amide (O=C) and the azomethine nitrogen.
The reactions of titanium(IV) chloride with salicylidene-2-aminopyridine (sapH) and alkyl xanthate (KS 2COR) in the 1:1 and 1:2 molar ratio(s) yield complexes of the type [(μ-Cl) 2Ti 2(Cl) 4(sap) 2] (1), [(η 5-C 5H 5) 4 Ti 2(μ-Cl) 2(η;2-S 2COR) 2] (2) (where R = C 6H 13) and [(Cl) 2Ti(sap) 2] (3) respectively. The complex 2 has been further treated with sodium salts of Schiff base (derived from isatin and aniline) and tetraisopropoxyaluminate in equimolar ratio to produce mixed ligand complexes of the type [(η 5-C 5H 5) 2Ti(η 2-S 2COR)(sb)] (4) and [(η 5-C 5H 5) 2 i(η 2- S 2COR)(μ-OPr i) 2{Al(OPr i)}] (5) respectively. All these complexes have been characterized by elemental analysis (Ti, Cl, C, H, N and S) and spectroscopic data [UV-visible, IR, NMR ( 1H and 13C), FAB-MS] and PXRD as well as thermogravimetric analysis.
The solid complexes of Co(II), Ni(II), Cu(II) and Zn(II) with tridentate Schiff base (PDBAA) derived from p-dimethylamino benzaldehyde and anthranilic acid have been synthesized and characterized by elemental analysis, molar conductivity, IR, 1H NMR, electronic spectra, magnetic susceptibility and X-ray diffraction spectra. From the analytical and spectral data, the stoichiometry of the complexes has been found to be 1 : 1 (metal : ligand). The metal chelates have a general formula [M(PDBAA)-H2O] where M = Co(II), Ni(II), Cu(II) and Zn(II). IR spectral data suggest that the ligand PDBAA behaves as a monobasic tridentate ligand with N : N : O donor sequence towards metal ions. Magnetic susceptibility measurement indicates paramagnetic behaviour of all complexes except zinc complex. X-ray diffraction studies suggest monoclinic crystal system for these complexes.
In the present synthesis, resulting Schiff bases who is bearing chloro, methoxy and methyl groups have been synthesized by the condensation between the primary amine and various subs tituted aromatic aldehydes in the presence of pyridine as a condensing agent. The newly prepared substituted schiff bases have been characterized and established on the basis of their elemental analysis, physical properties and spectral studies viz: IR.
The solid complex of Ni (II) with tetradentate schiff base (PDMBA) derived from pdimethylaminobenzaldehyde and o-aminobenzoic acid have been synthesized and characterized by molar conductivity, elemental analysis, IR, 1H NMR, magnetic susceptibility, electronic spectra and X-ray diffraction spectra. From the analytical and spectral data, the stoichiometry of the complex has been found to be 1: 1 (metal: ligand). The metal chelates have a general formula [Ni (PDMBA) H 2O]. IR spectral data suggest that the lignad PDMBA behave as monobasic tetradentate lignad with N: N: O: O - donor sequence towards metal ions. Magnetic susceptibility measurement indicates paramagnetic behaviour of complex.
A Schiff base ligand derived from o - hydroxy benzaldehyde and 2 - amino pyridine and its transition metal complexes with Fe(II), Cu(II), Ru(III) and Rh(III) have been synthesized which were characterized by elemental analysis, molar conductance, magnetic susceptibility, electronic spectra, IR and ESR spectroscopy. The metal complexes are coloured, solid and non - hygroscopic in nature. The Schiff base ligand exhibits tridentate nature, coordination through azomethine nitrogen, phenolic oxygen and nitrogen of pyridine ring to the metal ions. On the basis of electronic spectral analysis and magnetic susceptibility values, geometry of complexes were proposed to be octahedral. The molar conductivity data of complexes suggests their non - electrolytic nature. The ligand and metal complexes have been screened for their microbiological activity.
Schiff bases show a wide variety of applications of great importance in medicinal research due to their range of biological activities, where some Schiff bases are known to be promising antifungal agents. In this article we describe the electronic structure, optical, redox and antifungal properties of (E)-2-[(2-amino-pyridin-3-ylimino)-methyl]-4,6-di-tert-butyl-phenol (L1) and (E)-2-[(4-amino-pyridin-3-ylimino)-methyl]-4,6-di-tert-butyl-phenol (L2), two isomers phenol derivatives Schiff bases exhibiting a strong intramolecular hydrogen bond (O-H•••N). These compounds were characterized by their 1H, HHCOSY, 13C-NMR, FT-IR spectra, and by cyclic voltammetry. All the experimental results were complemented with theoretical calculations using density functional theory (DFT) and time-dependent DFT (TDDFT). The antimicrobial activity of the compounds described herein was assessed by determining the minimal inhibitory concentration (MIC) and by a modification of the Kirby-Bauer method. We tested Salmonella enterica serovar Typhi (S. Typhi, Gram-negative bacteria), Cryptococcus spp. (yeast), and Candida albicans (yeast). We found that neither L1 nor L2 showed antimicrobial activity against S. Typhi or Candida albicans. On another hand, L2, in contrast to L1, exhibited antifungal activity against Cryptococcus spp. (MIC: 4.468 µg/mL) even better than commercial antifungal medicaments. We mentioned above that L1 and L2 are isomers, because the amino groups is in ortho-position in L1 and in para-position in L2, however no significant differences were detectable by UV-vis, FT-IR, oxidation potentials and TDDFT calculations, but the antifungal activity served in Cryptococcus spp clearly differentiated between both isomers.
Schiff base ligand (L) was synthesized using 3-hydroxy benzaldehyde and 3-hydroxy-2-naphthoic hydrazide. The complexes of cobalt(II), nickel(ii) and palladium(ii) with this bidentate ligand were synthesized having metal:ligand stoichiometry 1:2 or 1:1. The ligand and respective complexes were characterized for their analytical parameters and various spectral features. The structures of these complexes were proposed on the basis of elemental analysis, molar conductivity, IR, 1H NMR, thermogravimetric method, electron absorption spectra and X-ray diffraction. The IR spectral data suggest that the ligand (L) behaves as a monobasic bidentate ligand with nitrogen and oxygen donor atoms towards metal ions. Magnetic susceptibility measurement indicates paramagnetic behaviour for Co(II), Ni(II) complexes and diamagnetic behaviour for Pd(II) complex. X-ray diffraction studies suggest ortho-rhombic crystal system for all the complexes.
We depict the synthesis of two new Schiff base ligands, formed by the condensation of 2-hydroxy-3-methoxybenzaldehyde with 2-amino-5-methylpyridine or 2-amino-5-bromopyridine. All of these ligands have been characterized on the basis of elemental analysis, IR, 1H NMR and Mass spectral data. The molecular geometry of 2-(5-methyipyridin-2-ylimino)methyl)-6-methoxyphenol has been determined by single crystal X-ray study. It reveals that this ligand exist in phenol-imine tautomeric form in the solid state. The reaction of these ligands with CuII and NiII resulted in the formation of mononuclear complexes having the general composition [ML1• NO3]•H2O. These complexes have been characterized on the basis of elemental analysis, metal-estimation, molar conductivity, IR, UV-Visible, ESI-Mass, thermal analysis and magnetic measurements. Non-electrolytic behavior of complexes indicates the absence of counter ion. The studies indicate a square planar geometry of the metal complexes. The Schiff base ligands and their metal complexes have been tested for antimicrobial activity against Gram-positive bacteria; Staphylococcus aureus and Bacillus subtilis and Gram-negative bacteria; Escherichia coli and Pseudomonas aeruginosa.
Schiff bases are versatile ligands which are synthesized from the condensation of primary amines with carbonyl groups. These compounds are very important in medicinal and pharmaceutical fields because of their wide spectrum of biological activities. Most of them show biological activities such as antibacterial, antifungal as well as antitumor activity. Transition metal complexes derived from the Schiff base ligands with biological activity have been widely studied. This review summarizes the synthesis and biological activities of Schiff bases and its complexes.
This paper reports the synthesis and a detailed investigation in solution, through (1)H NMR, optical absorption, fluorescence spectroscopy and second-order nonlinear optical studies, on the structure and photophysical properties of a series of unsymmetrical alkoxy-derivatized Schiff-base Zn(II) species bearing on one side an alkyl ammonium bromide as a Lewis base. Overall results suggest that these complexes are present in solution of dichloromethane as dimeric aggregates in which each molecular unit mutually interacts with another unit through intermolecular ZnBr(-) interactions. This represents an alternative approach to control the supramolecular architecture of Lewis acidic, Schiff-base Zn(II) complexes.
High-spin new, manganese-(II) L2MnCl2, complex has been synthesized and its structure was elucidated by using elemental analysis, FT-IR, DTA-TG, H-NMR, C-NMR and UV-Visible spectroscopic techniques. The structure of the compound has also been examined crystallographically. The title compound crystallizes in the triclinic space group P-1, with unit cell parameters: a = 11.354(1), b = 11.868(1), c = 12.080(1) Å, V = 1548.9(1) Å, Dx = 1.270 g.cm and Z = 2, respectively. The Mn atom was tetra-coordinated to form a distorted tetrahedral geometry by two oxygen atoms of L2 and two chloride atoms of MnCl2.4H2O in the complex.
Structural modification of organic molecule has considerable biological relevance. Further, coordination of a biomolecules to the metal ions significantly alters the effectiveness of the biomolecules. In view of the antimicrobial activity ligand ( bis -(2-aminobenzaldehyde)) malonoyl dihydrazone), metal complexes with Cu(II), Ni(II), Zn(II) and oxovanadium(IV) have been synthesized and found to be potential antimicrobial agents. An attempt is also made to correlate the biological activities with geometry of the complexes. The complexes have been characterized by elemental analysis, molar conductance, spectra and cyclicvoltammetric measurements. The structural assessment of the complexes has been carried out based on electronic, infrared and molar conductivity values.
(E)-2-[(2-chlorobenzylimino)methyl]methoxyphenol has been synthesized from the reaction of 2-hydroxy-3-methoxy-1-benzaldehyde(o-vanillin) with 2-chlorobenzylamine. The title compound has been characterized by using elemental analysis, FT-IR, (1)H NMR, (13)C NMR and UV-vis spectroscopic techniques. The crystal structure of the title compound has also been examined cyrstallographically. It crystallizes in the orthorhombic space group Pbca with unit cell parameters: a = 7.208(1) A, b = 13.726(2) A, c = 27.858(4) A, V = 2756.0(1) A(3), D(c) = 1.18 g cm(-3) and Z = 8. The crystal structure was solved by direct methods and refined by full-matrix least squares to a find R = 0.046 for 2773 observed reflections.
Plasticized membranes using Schiff Base complexes, derived from 2,3-diaminopyridine and o-vanilin have been prepared and explored as Cu(2+)-selective sensors. Effect of various plasticizers viz., dibutyl phthalate (DBP), dioctylphthalate (DOP), chloronaphthalene (CN), tri-n-butylphosphate (TBP) etc. and anion excluder, sodium tetraphenylborate (NaTPB) was studied in detail and improved performance was observed at several instances. Optimum performance was observed with Schiff Base (B) having a membrane composition of B(1%):PVC(33%):DOP(65%):NaTPB(1%). The sensor works satisfactorily in the concentration range 5.0x10(-6) to 1.0x10(-1)M (detection limit 0.3ppm) with a Nernstian slope of 29.6mV per decade of activity. Wide pH range (1.9-5.2), fast response time (<30s), high non-aqueous tolerance (up to 20%) and adequate shelf life (>4 months) indicate the vital utility of the proposed sensor. The potentiometric selectivity coefficient values as determined by match potential method (MPM) indicate good response for Cu(2+) in presence of interfering ions. The tolerance level of Hg(2+), which causes serious interference in the determination of Cu(2+) ions (K(Cu(2+)Hg(2+))(Pot)(MPM): 0.45), was determined as a function of Cu(2+) concentration in simulated mixtures. The sensor was also used in the potentiometric titration of Cu(2+) with EDTA.
Electronic absorption and emission properties of a series of Schiff bases derived from 2-hydroxy-3-methoxybenzaldehyde and 2-aminopyridine, 2,3-diaminopyridine, 2,6-diaminopyridine, or 3-aminomethylpyridine were studied in solvents of different polarities. The interconversion of the enolimine to the ketoamine tautomeric form was observed for compound 1, 6-methoxy-2-(3-pyridylmethyliminomethyl)phenol, and the corresponding equilibrium constant was estimated in several solvents. Protonation constants of all the investigated compounds were determined spectrophotometrically in the methanol/water 1/4 system. The effect of copper(II) ions on absorption and on the emission spectra of these ligands was examined in the buffered dioxane/water 1/1 system (pH 5.8). Strong complexation of Cu(II) and formation of a 1:1 complex were observed for the bis-Schiff base derived from 2,3-diaminopyridine. The complex of copper(II) with compound 1 was isolated and characterized by elemental analysis, magnetic susceptibility measurement, UV-vis and IR spectrometry.
The Schiff bases 2-amino-3-salicylideneaminopyridine (1) and 2,3-bis(salicylideneamino)pyridine (bimorphous, 2a and 2b) were prepared and characterized by X-ray crystallography and by IR and NMR spectrometry. (1) C12H11N3O, M(r) = 213.240, monoclinic, space group P2(1)/c, a = 12.00(2), b = 6.594(3), c = 14.06(2) angstrom, beta = 104.90(8)-degrees, V = 1075(2) angstrom3, Z = 4, D(x) = 1.317 g cm-3, lambda(Mo Kalpha) = 0.71073 angstrom, mu = 0.82 cm -1, F(000) = 448, T = 295 K, R = 0.047, R(w) = 0.028 for 886 reflections with I > 2sigma(I). (2a) C19H15N3O2, M(r) = 317.348 monoclinic, space group P2,, a = 6.202(3), b = 17.622(7), c = 14.724(8) angstrom, beta = 91.85(3)-degrees, V = 1608(1) angstrom3, Z = 4 (two crystallographically independent molecules A and B), D(x) = 1.311 g cm-3, lambda(Mo Kalpha) = 0.71073 angstrom, mu = 0.816 cm-1, F(000) = 664, T = 295 K, R = 0.058, R(w) = 0.034 for 972 reflections with I > 3sigma(I). The angle between the benzene and the pyridine ring is 51.5(2)-degrees in 1, whereas in 2a the corresponding angles are 51.1(4)-degrees in molecule A and 51.8(4)-degrees in molecule B. Molecules of 1 are connected in pairs by two centrosymmetric hydrogen bonds N-H...N(Py) of 3.024(5) angstrom. Intermolecular bonding of 1 does not take place in CHCl3 solution. No evidence was found in the IR and NMR spectra for tautomeric interconversion of 1 and 2 into the ketoamine or for cyclization of 2 into the cyclic diamine.
Preparation of 3-arylideneamino-2-aminopyridines (I), 2-aryl-1H-2, 3-dihydroimidazo (4, 5-b) pyridines (III) and 2-aryl-1H-imidazo (4, 5-b) pyridines (IV), by the condensation of pyridine-2, 3-diamine with aromatic aldehydes under different conditions is described.
Five-coordinate iron(II) complexes prepared from Schiff base ligands and pyridine have been synthesized. The Schiff base ligands were formed from salicylaldehyde or 5-bromosalicylaldehyde and ethylenediamine or o-phenylenediamine. Three of the four complexes react with oxygen in the solid state to produce five-coordinate μ-oxo compounds. The formation of a μ-oxo complex in the solid state is compared with the reaction of dioxygen and hemerythrin to form methemerythrin. For both systems a dioxygen complex intermediate is proposed which is stabilized in the case of hemerythrin. The relevance of the Schiff base complexes as model compounds is discussed.