Synthesis, structural and spectral studies of Cu(II) and V(IV) complexes of a novel Schiff base derived from pyridoxal. Antimicrobial activity

A novel Schiff base, N-(4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one)pyridoxaldimine (HL·HCl), was prepared and structurally characterized on the basis of elemental analyses, ¹H and ¹³C NMR, and IR spectral data. The synthesis and characterization of several Cu(II) (1-6) and V(IV) (7) complexes with N-(4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one)pyridoxaldimine are reported. The composition and structures of the copper(II) and vanadium(IV) complexes were proposed based on elemental analyses, molar conductance, magnetic susceptibility measurements, IR, electronic and EPR spectroscopy. In addition, the structures of the ligand and the complex [CuL(H₂O)₂]NO₃·2.25H₂O (1) have been determined by single-crystal X-ray diffraction, showing that the Cu(II) center has a distorted square-pyramidal geometry. The ligand and the complexes were also tested for their in vitro antibacterial activity.     

Synthesis,characterization and antibacterial activity of some new complexes of Cu(II), Ni(II), VO(II), Mn(II) with Schiff base derived from 4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one

Coordination compounds of Cu(II), VO(II), Ni(II), and Mn(II) with the Schiff base obtained through the condensation of 4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one with 3-formyl-6-methyl-chromone were synthesized. The characterization of the newly formed compounds was done by ¹H NMR, UV–Vis, IR, ESR spectroscopy, elemental analysis and molar electric conductibility. The crystal structure of 1-phenyl-2,3-dimethyl-4-(N-3-formyl-6-methyl-chromone)-3-pyrazolin-5-one (HL) has been determined by X-ray diffraction studies, as well as the one of its copper(II) complex [CuL(OAc)]·CH₃OH which contains an anionic ligand and an acetate in the coordination sphere of the metal. The single crystal X-ray structure for (HL) was analyzed for its various weak H-bonding and dimeric association.     

Some new Cu(II) complexes containing an ON donor Schiff base: Synthesis, characterization and antibacterial activity

Six new copper(II) complexes, CuLCl·H₂O (1), CuL(NO₃)·2H₂O (2), [Cu(L)₂] (3), CuL(SCN)·2H₂O (4), CuL(ClO₄)·2H₂O (5) and (CuL)₂(SO₄)·4H₂O (6), where HL = 1-phenyl-2,3-dimethyl-4-(N-2-hydroxy-4-methoxy-benzaldehyde)-3-pyrazolin-5-one, have been synthesized. The characterization of the newly formed compounds was done by ¹H NMR, UV-Vis, IR, ESR spectroscopy, elemental analysis and molar electric conductivity. The crystal structure of 1-phenyl-2,3-dimethyl-4-(N-2-hydroxy-4-methoxy-benzaldehyde)-3-pyrazolin-5-one has been determined by X-ray diffraction studies, as well as the crystal structure of one of its copper(II) complexes, [Cu(L)₂] (3). The copper atom is coordinated to two nitrogen and two oxygen atoms of the Schiff base ligand. The in vitro antibacterial activity against Klebsiella pneumoniae ATCC 100131, Staphylococcus aureus var. Oxford 6538, Pseudomonas aeruginosa ATCC 9027 and Escherichia coli ATCC 10536 strains was studied and compared with that of free ligand. The anti-microbial activity was dependent on the microbial species tested and the metal salt anion used.     

Synthesis, spectral characterization of Schiff base transition metal complexes: DNA cleavage and antimicrobial activity studies

A new series of transition metal complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), VO(IV), Hg(II) and Cd(II) have been synthesized from the Schiff base (L) derived from 4-aminoantipyrine, 3-hydroxy-4-nitrobenzaldehyde and o-phenylenediamine. Structural features were obtained from their elemental analyses, magnetic susceptibility, molar conductance, mass, IR, UV-Vis, ¹H NMR and ESR spectral studies. The data show that these complexes have composition of ML type. The UV-Vis, magnetic susceptibility and ESR spectral data of the complexes suggest a square-planar geometry around the central metal ion except VO(IV) complex which has square-pyramidal geometry. The redox behaviour of copper and vanadyl complexes was studied by cyclic voltammetry. Antimicrobial screening tests gave good results in the presence of metal ion in the ligand system. The nuclease activity of the above metal complexes shows that Cu, Ni and Co complexes cleave DNA through redox chemistry whereas other complexes are not effective.     

Synthesis,spectral characterization and biological studies of transition metal(II) complexes with triazole Schiff bases

New metal based triazoles (1–12) have been synthesized by the interaction of novel Schiff base ligands (L¹–L³) with the Co(II), Ni(II), Cu(II) and Zn(II) metal ions. The Schiff base ligands and their all metal(II) complexes have been thoroughly characterized using various physical, analytical and spectroscopic techniques. In vitro bacterial and fungal inhibition studies were carried out to examine the antibacterial and antifungal profile of the Schiff bases in comparison to their metal(II) complexes against two Gram‐positive, four Gram‐negative and six fungal strains. The bioactivity data showed the metal(II) complexes to have more potent antibacterial and antifungal activity than their uncomplexed parent Schiff bases against one or more bacterial and fungal species. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis,characterization, and antimicrobial activity of two Schiff base silver(I) complexes derived from 4-carboxybenzaldehyde

Two new Schiff base silver(I) complexes, {[Ag(L¹)][H₂O]}_∞ (1) and {[Ag(L²)][H₂O]}_∞ (2), where L¹ = 4-((2-diethylaminoethylimino)methyl)phenecarboxylate and L² = 4-([3-(morpholin-4-yl)propyl]iminomethyl)phenecarboxylate, have been synthesized and characterized. X-ray crystallographic analysis reveals that silver ions in 1 are bridged by L¹ to form a one-dimensional zigzag chain, while three silver ions in 2 are linked by L² to produce a two-dimensional coordination polymer. Guest water molecules in 1 generate a one-dimensional hydrogen-bonded chain. Both 1 and 2 offer high antibacterial activity against Gram-positive bacteria Staphylococcus aureus with MIC values of 0.26 and 0.24 mM and to exhibit good inhibitory activity against urease with the respective IC₅₀ values of 3.5 ± 0.1 and 3.8 ± 0.2 μM.     

Metal complexes of Schiff base derived from sulphametrole and o-vanilin. Synthesis, spectral, thermal characterization and biological activity

Metal complexes of Schiff base derived from condensation of o-vanilin (3-methoxysalicylaldehyde) and sulfametrole [N(1)-(4-methoxy-1,2,5-thiadiazole-3-yl)sulfanilamide] (H2L) are reported and characterized based on elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, molar conductance, mass spectra, UV-vis and thermal analysis (TGA). From the elemental analyses data, the complexes were proposed to have the general formulae [M2X3(HL)(H2O)5].yH2O (where M=Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), X=Cl, y=0-3); [Fe2Cl5(HL)(H2O)3].2H2O; [(FeSO4)2(H2L)(H2O)4] and [(UO2)2(NO3)3(HL)(H2O)].2H2O. The molar conductance data reveal that all the metal chelates were non-electrolytes. The IR spectra show that, H2L is coordinated to the metal ions in a tetradentate manner with ON and NO donor sites of the azomethine-N, phenolic-OH, enolic sulphonamide-OH and thiadiazole-N. From the magnetic and solid reflectance spectra, it is found that the geometrical structures of these complexes are octahedral. The thermal behaviour of these chelates shows that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The activation thermodynamic parameters, such as, E*, DeltaH*, DeltaS* and DeltaG* are calculated from the DrTG curves using Coats-Redfern method. The synthesized ligand, in comparison to their metal complexes also were screened for their antibacterial activity against bacterial species, Escherichia coli, Salmonella typhi, Bacillus subtillus, Staphylococcus aureus and Fungi (Aspergillus terreus and Aspergillus flavus). The activity data show that the metal complexes to be more potent/antimicrobial than the parent Shciff base ligand against one or more microbial species.     

Synthesis,spectral characterization and structural investigation on some 4-aminoantipyrine containing Schiff base Cu(II) complexes and their molecular association

Compounds [Cu(L₁)₂] (1) and [Cu(L₂)₂] (2), where L₁ and L₂ are Schiff base ligands of 4-aminoantipyrine and substituted salicylaldehydes, were synthesized and characterized using various spectroscopic techniques such as elemental analysis, UV–Vis, IR, and NMR. The single crystal X-ray structures for L₁, L₂, and their corresponding Cu(II) complexes assembled in a 1:2 metal to ligand ratio were analyzed for their various weak H-bonding and dimeric association. The structural analysis of compounds 1 and 2, being the first crystal structures in this series, deserves special attention to help further the understanding in this area of structure–reactivity correlation studies. Further these compounds, composed of very similar chemical composition with a small difference in the substituent on the salicylaldehyde moiety, influenced through various weak inter- and intramolecular H-bonding and C–H?π interactions, rearrange the geometry around Cu(II) from a tetrahedrally distorted square planar geometry in [Cu(L₁)₂] (1) to square planar in [Cu(L₂)₂] (2). Steric strain imposed by the methyl substitution on the 4-aminoantipyrine moiety of the Schiff base ligand, causing this small change of the Cu(II) geometry, along with various weak interactions is analyzed in detail.     

Antibacterial activity of transition metal complexes with a tridentate NNO amoxicillin derived Schiff base. Synthesis and characterization

From the reaction of amoxicillin ( 1 ) antibiotic with 2,6?diaminopyridine ( 2 ) an amoxicillin?based Schiff base (HL) ( 3 ) was obtained and its transition metal Schiff base complexes were synthesized. Spectroscopic and physicochemical techniques, namely, UV?Vis, FT?IR, ¹H?NMR, EPR, mass spectrometry, molar conductance, magnetic susceptibility, molecular modelling, together with elemental and thermal analyses, were used to characterize the synthesized compounds. Spectral and magnetic data suggested an octahedral geometry for all the complexes and the general formulae [ML(H₂O)₃][PF₆] (M(II) = Mn²⁺ ( 4 ), Co²⁺ ( 5 ), Ni²⁺ ( 6 ), Cu²⁺ ( 7 ), Zn²⁺ ( 8 ), was proposed for them, where L represents deprotonated tridentate NNO amoxycillin?derived Schiff base. All compounds were screened for antibacterial activity by using agar disc diffusion method. The zinc(II) complex exhibited promising bactericidal activity against E. coli and S. aureus.     

Synthesis,crystal feature and spectral characterization of paeonol derived Schiff base ligands and their Cu(II) complexes with antimicrobial activity

Four novel Schiff bases PNL-4OMe, PNL-4Br, PNL-4F, PNL-3,4-F₂, and their copper(II) complex with [M(L)₂(H₂O)₂] arrangement was synthesized using Paeonol and various aromatic substituted amines. Characterization has been done through FT-IR, ESI Mass, TG-DTA, DFT, magnetic measurements, elemental analysis, and Thermogravimetric analysis. Paeonol derived new bond formation in Schiff bases and changes in frequencies during complexation have been confirmed through FT-IR spectra. All complexes are thermally stable, paramagnetic, and have non-electrolytic behavior. The antimicrobial activity was also tested against Gram-positive bacteria; S. aureus, B. subtilis, and Gram-negative bacteria; E. coli, P. aeruginosa. Single-crystal X-ray data provide evidence that PNL-3,4-F₂ is recrystallizing in a triclinic system with P-1(2) space group and confirms the intramolecular H-bonding and short Vander Waal type interactions. Non-covalent interactions and π … π stacking surface interactions in PNL-3,4-F₂ were studied with Hirshfeld analysis. H-atoms have the highest interactions with other atoms of neighbouring molecules compared to all other atoms. DFT calculations were performed on the electronic structure of ligand PNL-3,4-F₂ and its copper(II) complex and discussed.     

Synthesis,characterization, NLO study,and antimicrobial activities of metal complexes derived from 3-(3-(2-hydroxyphenyl)-3-oxoprop-1-enyl)-4H-chromen-4-one and sulfanilamide

A series of metal(II) complexes ML (where M?=?Cu(II), Co(II), Ni(II), Zn(II), Mn(II), Cd(II), and VO(II)) have been prepared from 3-(3-(2-hydroxyphenyl)-3-oxoprop-1-enyl)-4H-chromen-4-one and sulfanilamide. The structures of the complexes have been investigated by elemental analysis, magnetic susceptibility, molar conductance, IR, UV-Vis, NMR, mass, and ESR spectral studies. Conductivity measurements reveal that the complexes are non-electrolytes, except the oxovanadium complex. Spectral and other data show square pyramidal geometry for oxovanadium and octahedral for the other complexes. The redox behaviors of the copper and vanadyl complexes have been studied through cyclic voltammetry. Antimicrobial activities of the compounds against several microorganisms indicate that some complexes have higher activity than free ligand. The compounds may serve as photoactive materials as indicated from their characteristic fluorescence properties. The second harmonic generation efficiency of the ligand was found to be higher than that of urea and KDP.     

Synthesis, spectroscopic, thermal and antimicrobial studies of some novel metal complexes of Schiff base derived from [N1-(4-methoxy-1,2,5-thiadiazol-3-yl)sulfanilamide] and 2-thiophene carboxaldehyde

Keeping in view the chemotherapeutic of the sulfa-drugs, Schiff base namely 2-thiophene carboxaldehyde-sulfametrole (HL) and its tri-positive and di-positive metal complexes have been synthesized and characterized by elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, molar conductance, mass spectra, UV-vis and thermal analysis (TGA and DrTG). The low molar conductance values suggest the non-electrolytic nature of these complexes. IR spectra show that HL is coordinated to the metal ions in a tetradentate manner through hetero five-membered ring-S and azomethine-N, enolic sulfonamide-OH and thiadiazole-N, respectively. Zn(II), Cd(II) and UO2(II) complexes are found to be diamagnetic (as expected). The proposed general formulae of the prepared complexes are [M2X4(HL)(H2O)4] (where M=Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), X=Cl, [Fe2Cl6(HL)(H2O)2], [(FeSO4)2(HL)(H2O)4] and [(UO2)2(HL) (NO3)4].H2O. The thermal behaviour of these chelates shows that the hydrated complexes loss water of hydration in first step in case of uranium complexes followed loss coordinated water followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The activation thermodynamic parameters, such as DeltaE*, DeltaH*, DeltaS*, and DeltaG* are calculated from the DrTG curves using Coats-Redfern method. The antimicrobial activity of the obtained products was performed using Chloramphenicol and Grisofluvine as standards, indicate that in some cases metallation increase activity than the ligand.     

Synthesis,characterization and bioactivity of Schiff base copper(II) complexes derived from L-glutamine and L-asparagine

To investigate the structure–activity relationship of L-glutamine and L-asparagine Schiff base copper complexes in applications, L-glutamine and L-asparagine Schiff bases (GV and AV) and their copper complexes [Cu₃(GV)₂(CH₃COO)₂(H₂O)] · 2H₂O (GVC) and [CuAV(H₂O)₃] (AVC) have been synthesized and characterized by molar conductance, elemental analysis, UV-Vis, IR, ¹H-NMR, and TG-DTG. We examined the geometries of GV, AV, GVC, and AVC through Hartree–Fock method and electronic absorption spectra. We also tested their antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis bacteria and antiproliferation activity on human breast cancer MDA-MB-231 cells. The side chain difference between L-glutamine and L-asparagine results in different geometry of GV and AV, which leads to different geometry of GVC and AVC. GVC, a trinuclear Cu(II) complex, shows the highest antibacterial activity and the highest growth inhibition activity on MDA-MB-231 cells. Our results suggest that GVC has potential as an antibacterial and anticancer agent.     

Some divalent metal(II) complexes of salicylaldehyde‐derived Schiff bases: Synthesis,spectroscopic characterization,antimicrobial and in vitro anticancer studies

Mononuclear transition metal(II) complexes of the type M(L)₂?2H₂O (where M = Co, Ni, Cu, Zn) have been synthesized from uninegative Schiff base ligands (HL₁–HL₄) designed by condensation of 4‐fluorobenzylamine with 2‐hydroxy‐1‐naphthaldehyde/3,5‐dichlorosalicylaldehyde/3,5‐dibromosalicylaldehyde/3‐bromo‐5‐chlorosalicylaldehyde. The compounds were successfully characterized using spectroscopic and physiochemical methods together with elemental analysis. Spectroscopic elucidation indicates a monobasic bidentate nature of ligands coordinated via deprotonated phenolic oxygen and azomethine nitrogen atom which suggests an octahedral geometry around the central metal ions. The complexes and ligands were screened for their in vitro antimicrobial activity against bacterial and fungal strains, the zinc(II) complexes being more active against the tested microbial strains. Further, the metal complexes were found to be more active than the uncomplexed ligands due to chelation process and, moreover, the complexes were more active against fungal strains than bacterial strains. Cytotoxic activities of all compounds were evaluated towards human alveolar adenocarcinoma epithelial cell line (A549), human breast adenocarcinoma cell line (MCF7), human prostate cancer cell line (DU145) and one normal human lung cell line (MRC‐5) using MTT colorimetric assay with doxorubicin as a standard. The zinc complexes were most active against the cancer cell lines and also found to be less toxic against MRC‐5 normal cell line than standard doxorubicin.     

Synthesis, spectral, antimicrobial and antitumor assessment of Schiff base derived from 2-aminobenzothiazole and its transition metal complexes

N-(thiophen-2-ylmethylene)benzo[d]thiazol-2-amine Schiff base (L) derived from 2-aminobenzothiazole and 2-thiophenecarboxaldehyde was synthesized and characterized using elemental analysis, IR, mass spectra, (1)H NMR and UV-vis spectra. Its complexes with Cu(II), Fe(III), Ni(II) and Zn(II) were prepared and isolated as solid products and characterized by elemental and thermal analyses, spectral techniques as well as magnetic susceptibility. The IR spectra showed that the Schiff base under investigation behaves as bidentate ligand. The UV-vis spectra and magnetic moment data suggested octahedral geometry around Cu(II) and Fe(III) and tetrahedral geometry around Ni(II) and Zn(II). In view of the biological activity of the Schiff base and its complexes, it has been observed that the antimicrobial activity of the Schiff base increased on complexation with the metal ion. In vitro antitumor activity assayed against five human tumor cell lines furnished the significant toxicities of the Schiff base and its complexes.     

Synthesis and characterization of heteroleptic Schiff base transition metal complexes: a study of anticancer,antimicrobial, DNA cleavage and anti-TB activity

In search of effective bioactive compounds, we have synthesized the new Co(II), Ni(II), and Cu(II) complexes of the Schiff base derived from 8-formyl-7-hydroxy-4-methylcoumarin and 2-hydrazino benzothiazole and characterized by analytical, spectroscopic (IR, NMR, UV–vis, Mass), magnetic, powder X-ray diffraction data (PXRD) and TGA studies. Elemental analysis suggests the stoichiometry of the synthesized complexes and the solution electronic spectral study revealed the octahedral geometry of the compounds. Thermal analysis shows the presence of water molecule outside the coordination sphere and powder-XRD patterns have been studied to test the degree of crystallinity of the complexes and unit cell calculations were made. All the synthesized compounds were tested against human ovarian cancer cell line (PA-1). The synthesized metal complexes exhibited enhanced activity against the tested bacterial (Staphylococcus aureus and Escherichia Coli) and fungal strains (Candida albicans and Aspergillus fumigatus) as compared to free ligand (LH). The results of the DNA-cleavage activity suggest that the ligand and its metal complexes can cleave CT-DNA at different degrees. Further, anti-tuberculosis activity was done using microplate almar blue assay. Among all these synthesized compounds, the Cu(II) complex exhibits good cleaving ability compared to other newly synthesized metal complexes.     

Spectral characterization,electrochemical, antimicrobial and cytotoxic studies on new metal(II) complexes containing N2O4 donor hexadentate Schiff base ligand

We report the biological activity of the new Schiff base ligand H₂L (H₂L = 6,6′-((1E,11E)-5,8-dioxa-2,11-diazadodeca-1,11-diene-1,12-diyl)bis(2,4-dichlorophenol)), its derived metal(II) complexes [Cu(L)] (1), [Co(L)] (2), [Ni(L)] (3) and [Zn(L)] (4), along with their structural characterizations by using various analytical and spectroscopic techniques. Electrochemical investigations showed that all of these Cu(II), Co(II) and Ni(II) complexes were reversibly reducible. Although the change of the number of unpaired electrons are different of the metal cations, they have an effect on the redox potentials of the Co(II)/(I), Ni(II)/(I) and Cu(II)/(I) couples. The ¹H NMR and FTIR data concluded that the Schiff base ligand H₂L acts as a hexadentate ligand coordinating with metal(II) ions through the oxygen atoms of the (COC), phenolic (COH) groups and nitrogen atom of the azomethine (CHN) group. UV-Visible absorption spectra studies clearly revealed the octahedral geometry of the prepared metal(II) complexes. Complexes 1 and 4 were found to be efficient in bringing about antimicrobial activities. The proposed mechanism of their antimicrobial activities has been discussed. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed the remarkable cytotoxicity of complex 1 (IC50 = 17 ± 1.3 μg/mL) on human breast cancer MCF-7 cells than Schiff base ligand H₂L and complexes 2–4. Moreover, AO/EB staining assay revealed cell death due to apoptosis in MCF-7 cells and the generation of ROS by the Schiff base ligand H₂L and its derived metal(II) complexes 1–4 may be a possible cause for their cytotoxic activity.     

Synthesis,characterization, electrochemical,catalytic and antimicrobial activity studies of hydrazone Schiff base ruthenium(II) complexes

Four tridentate O, N, O donor Schiff base ligands were prepared by the reaction of substituted benzhydrazide and appropriate salicylaldehyde. The complexes of these ligands were synthesized by refluxing the ligands with ruthenium(II) starting complexes of the formula [RuHCl(CO)(EPh₃)₂B] in benzene, where E = P or As; B = PPh₃ or AsPh₃ or pyridine. The newly synthesized complexes were characterized by elemental, spectral (FT‐IR, UV and NMR) and electrochemical data. On the basis of the above studies, an octahedral structure has been proposed for all the complexes. The catalytic efficiency of the complexes in aryl–aryl couplings and oxidation of alcohols was examined and their inhibition activity against the growth of the micro‐organisms was also examined. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis, characterization and biological activity of some transition metals with Schiff base derived from 2-thiophene carboxaldehyde and aminobenzoic acid

Metal complexes of Schiff base derived from 2-thiophene carboxaldehyde and 2-aminobenzoic acid (HL) are reported and characterized based on elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, molar conductance and thermal analysis (TGA). The ligand dissociation as well as the metal-ligand stability constants were calculated pH metrically at 25 degrees C and ionic strength mu=0.1 (1M NaCl). The complexes are found to have the formulae [M(HL)2](X)n.yH2O (where M=Fe(III) (X=Cl, n=3, y=3), Co(II) (X=Cl, n=2, y=1.5), Ni(II) (X=Cl, n=2, y=1) and UO2(II) (X=NO3, n=2, y=0)) and [M(L)2] (where M=Cu(II) (X=Cl) and Zn(II) (X=AcO)). The molar conductance data reveal that Fe(III) and Co(II), Ni(II) and UO2(II) chelates are ionic in nature and are of the type 3:1 and 2:1 electrolytes, respectively, while Cu(II) and Zn(II) complexes are non-electrolytes. IR spectra show that HL is coordinated to the metal ions in a terdentate manner with ONS donor sites of the carboxylate O, azomethine N and thiophene S. From the magnetic and solid reflectance spectra, it is found that the geometrical structure of these complexes are octahedral. The thermal behaviour of these chelates shows that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The activation thermodynamic parameters, such as, E*, DeltaH*, DeltaS* and DeltaG* are calculated from the DrTG curves using Coats-Redfern method. The synthesized ligands, in comparison to their metal complexes also were screened for their antibacterial activity against bacterial species, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus pyogones and Fungi (Candida). The activity data show that the metal complexes to be more potent/antibacterial than the parent Schiff base ligand against one or more bacterial species.     

Synthesis and characterization of Co(II), Ni(II), Cu(II) and Zn(II) complexes of tridentate Schiff base derived from vanillin and DL-alpha-aminobutyric acid

Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived from vanillin and dl-alpha-aminobutyric acid were synthesized and characterized by elemental analysis, IR, electronic spectra, conductance measurements, magnetic measurements, powder XRD and biological activity. The analytical data show the composition of the metal complex to be [ML(H(2)O)], where L is the Schiff base ligand. The conductance data indicate that all the complexes are non-electrolytes. IR results demonstrate the tridentate binding of the Schiff base ligand involving azomethine nitrogen, phenolic oxygen and carboxylato oxygen atoms. The IR data also indicate the coordination of a water molecule with the metal ion in the complex. The electronic spectral measurements show that Co(II) and Ni(II) complexes have tetrahedral geometry, while Cu(II) complex has square planar geometry. The powder XRD studies indicate that Co(II) and Cu(II) complexes are amorphous, whereas Ni(II) and Zn(II) complexes are crystalline in nature. Magnetic measurements show that Co(II), Ni(II) and Cu(II) complexes have paramagnetic behaviour. Antibacterial results indicated that the metal complexes are more active than the ligand.