Synthesis,characterization and thermal study of some tetradentate Schiff base transition metal complexes

Several mononuclear Co(II), Ni(II), Cu(II), and Fe(II) complexes of tetradentate salpren-type diimine, obtained from 3,5-di-tert-butyl-2-hydroxybenzaldehyde and 1,3-diaminopropane have been prepared and characterized by analytical, spectroscopic (FT-IR, UV–VIS) techniques, magnetic susceptibility measurements and thermogravimetric analyses (TG). The thermodynamic and thermal properties of complexes have been investigated. For further characterization Direct Insertion Probe-Mass Spectrometry (DIP-MS) was used and the fragmentation pattern and also stability of the ions were evaluated. The characterization of the end products of the decomposition was achieved by X-ray diffraction. The thermal stabilities of metal complexes of N,N′-bis(3,5-di-t-butylsalicylidene)-1,3-propanediamine ligand (L) were found as Ni(II) > Cu(II) > Co(II) > Fe(II).     

Synthesis, characterization and thermal analysis of some new transition metal complexes of a polydentate Schiff base

A new polydentate Schiff base (H3L) was synthesized from the condensation of 2,6-diformyl-4-methylphenol and S-methylhydrazine-carbodithionate. The 1:1 metal complexes were obtained from the interaction of H3L and the metal ions Cr(III), Co(II), Ni(II), Cu(II), Cd(II) and Hg(II). The complexes were characterized by elemental analysis and IR spectroscopy. Detailed studies of the thermal properties of the complexes were investigated by thermogravimetry techniques.     

Preparation, characterization and thermal studies of some transition metal ternary complexes

Ternary complexes of Co(II), Ni(II), Cu(II) and Zn(II) with nitrilotriacetic acid as a primary ligand and glycine as secondary ligand were prepared in slightly acid medium. Their molecular masses were determined by acid-base titration against standard potassium hydroxide solution. Their molecular structures were found to be [M (HNTA)(glyH)(2H₂O)]. Thermogravimetric analysis confirmed this structure and that the water present is coordinated to the central metal atom. UV-Vis spectra showed that the complexes have octahedral symmetry. IR spectra suggested the presence of intermolecular hydrogen bonding. This phenomenon was supported by mass spectra. The ionization constants of these complexes, as diprotic acids, were determined.     

Synthesis,spectroscopic characterization and thermal studies of some rare earth metal complexes of unsymmetrical tetradentate Schiff base ligand

The solid complexes of La(III), Ce(III), Pr(III), Nd(III), Sm(III) and Gd(III) with 4-hydroxy-3-(1-{2-(2-hydroxy-benzylidene)-aminophenylimino}-thyl)-6-methy-pyran-2-one (H₂L) derived from o-phenylenediamine, 3-acetyl-6-methyl-(2H)pyran,2,4(3H)-dione (dehydroacetic acid or DHA) and salicylic aldehyde have been synthesized and characterized by elemental analysis, conductometry, magnetic susceptibility, UV–visible, FTIR, ¹H NMR spectra, X-ray diffraction, and thermal analysis and screened for antimicrobial activity. The FTIR spectral data suggest that the ligand behaves as a dibasic tetradentate ligand with ONNO donar atoms sequence towards central metal ion. From the microanalytical data, the stoichiometry of the complexes has been found to be 1:1 (metal:ligand). The physico-chemical data suggest distorted octahedral geometry for La(III), Ce(III), Pr(III), Nd(III), Sm(III) and Gd(III) complexes. The X-ray diffraction data suggest monoclinic crystal system for La(III) and Ce(III) and orthorhombic crystal system for Pr(III) and Nd(III) complexes. Thermal behaviour (TGA/DTA) of the complexes was studied and kinetic parameters were determined by Horowitz–Metzger and Coats–Redfern methods. The ligand and their metal complexes were screened for antibacterial activity against Staphylococcus aureus, Escherichia coli and Bacillus sp. Fungicidal activity against Aspergillus niger, Trichoderma and Fusarium oxysporum.     

Synthesis,characterization, and biological studies of some Schiff base complexes

The synthesis of a new Schiff base derived from 2-hydroxy-5-chloroacetophenone and 4-amino-5-mercapto-3-methyl-1,2,4-triazole and its coordination compounds with Ti(III), VO(IV), Cr(III), Mn(III), Fe(III), Zr(IV), MoO₂(VI), and UO₂(VI) are described. The ligand and the complexes have been characterized on the basis of analytical, electrical conductance, molecular weight, IR and electronic spectra, magnetic susceptibility measurements, and thermogravimetric analysis. The ligand acts as a dibasic tridentate molecule. Antibacterial activities of the ligand and its metal complexes have been determined by screening the compounds against E. coli, S. typhi, P. aeruginosa, and S. aureus. The solid state de electrical conductivity of the ligand and its complexes have been measured over 313–403 K, and the complexes were found to be of semiconducting nature. The article was submitted by the authors in English.     

Synthesis,characterization, and thermal analysis of transition metal complexes of polydentate ONO donor Schiff base ligand

Mn(II), Co(II), Ni(II), Cu(II), Cd(II), and Hg(II) metal complexes with Schiff bases derived from 3-formyl-4-hydroxycoumarin and semicarbazone are synthesized and characterized on the basis of elemental analysis, molar conductance, magnetic moment, IR, electronic, ¹H NMR spectrum, and ESR spectrum, TGA, and X-ray diffraction powder methods. Molar conductance values indicate that the complexes are nonelectrolytic in nature. Magnetic moment and spectral studies suggest either tetrahedral or square-planar geometry around the central metal ions. The analytical data indicate that metal-to-ligand stoichiometry in all complexes is 1: 1. The article was submitted by the authors in English.     

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,characterization, antifungal,antibacterial and DNA cleavage studies of some heterocyclic Schiff base metal complexes

Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived from indole-3-carboxaldehyde and m-aminobenzoic acid were synthesized and characterized by elemental analysis, molar conductance, IR, UV–Vis, magnetic moment, powder XRD and SEM. The IR results demonstrate the bidentate binding mode of the ligand involving azomethine nitrogen and carboxylato oxygen atoms. The electronic spectral and magnetic moment results indicate that Co(II) and Ni(II) complexes have tetrahedral geometry, while Cu(II) complex is square planar. Powder XRD and SEM indicate the crystalline state and surface morphology studies of the complexes. The antimicrobial activity of the synthesized ligand and its complexes were screened by disc diffusion method. The results show that the metal complexes were found to be more active than the ligand. The nuclease activity of the ligand and its complexes were assayed on CT DNA using gel electrophoresis in the presence of H₂O₂. The Cu(II) complex showed increased nuclease activity in the presence of an oxidant when compared to the ligand and other complexes.     

Synthesis,characterization, anticancer activity,thermal and electrochemical studies of some novel uranyl Schiff base complexes

Some tetradentate N₂O₂ Schiff base ligands, such as N,N′-bis(naphtalidene)-1,2-phenylenediamine, N,N′-bis(naphtalidene)-4-methyl-1,2-phenylenediamine, N,N′-bis(naphtalidene)-4-chloro-1,2-phenylenediamine, N,N′-bis(naphtalidene)-4-nitro-1,2-phenylenediamine, N,N′-bis(naphtalidene)-4-carboxyl-1,2-phenylenediamine, and their uranyl complexes were synthesized and characterized by ¹H NMR, IR, UV–Vis spectroscopy, TG (thermogravimetry), and elemental analysis (C.H.N.). Thermogravimetric analysis shows that uranyl complexes have very different thermal stabilities. This method is used also to establish that only one solvent molecule is coordinated to the central uranium ion and this solvent molecule does not coordinate strongly and is removed easier than the tetradentate ligand and also trans oxides. The electrochemical properties of the uranyl complexes were investigated by cyclic voltammetry. Electrochemistry of these complexes showed a quasireversible redox reaction without any successive reactions. Also, the kinetic parameters of thermal decomposition were calculated using Coats–Redfern equation. According to Coats–Redfern plots the kinetics of thermal decomposition of the studied complexes is first-order in all stages. Anticancer activity of the uranyl Schiff base complexes against cancer cell lines (Jurkat) was studied and determined by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide) assay.     

Antimicrobial activity and spectral, magnetic and thermal studies of some transition metal complexes of a Schiff base hydrazone containing a quinoline moiety

A series of new copper(II), cobalt(II), nickel(II), manganese(II), iron(III), and uranyl(VI) complexes of the Schiff base hydrazone 7-chloro-4-(benzylidene-hydrazo)quinoline (HL) were prepared and characterized. The Schiff base behaves as a monobasic bidentate ligand. Mononuclear complexes with the general composition [ML2(Cl)m(H2O)2(OEt)n] x xEtOH (M = Cu(II), Co(II), Ni(II), Mn(II), Fe(III) or UO2(VI); m and n = 0-1; x = 1-3) were obtained in the presence of Li(OH) as a deprotonating agent. The nature of bonding and the stereochemistry of the complexes have been deduced from elemental analyses, infrared, electronic spectra, magnetic susceptibility and conductivity measurements. An octahedral geometry was suggested for all the complexes except the Cu(II) and UO2(VI) ones. The Cu(II) complex has a square-planar geometry distorted towards tetrahedral, while the UO2(VI) complex displays its favored heptacoordination. The Schiff base ligand, HL, and its complexes were tested against one strain gram +ve bacteria (Staphylococcus aureus), gram -ve bacteria (Escherichia coli), and Fungi (Candida albicans). The prepared metal complexes exhibited higher antibacterial activities than the parent ligand and their biopotency is discussed.     

Synthesis and characterization of some Schiff base transition metal complexes derived from vanillin and L(+)alanine

The cobalt(II), nickel(II), copper(II) and zinc(II)-vanillidene-L(+)alanine complexes were synthesized and characterized by elemental analysis, conductivity measurements, magnetic behavior, infrared, electronic spectral measurements, X-ray powder diffraction and biological studies. The conductance measurements indicate that all the complexes are non-electrolytes. The infrared spectra indicate the coordination of imino nitrogen, phenolic oxygen and carboxylato oxygen atoms. The electronic spectral measurements demonstrate that cobalt(II) and nickel(II)-vanillidene-L(+)alanine complexes are tetrahedral, while copper(II)-vanillidene-L(+)alanine complex has square planar geometry. The cobalt(II) complex is found to be ferromagnetic. The powder XRD studies confirm the crystalline nature of the complexes. The ligand and complexes were less active against PN, PA and BC, whereas copper complex shows moderate activity against AN.     

Synthesis, structural, thermal studies and biological activity of a tridentate Schiff base ligand and their transition metal complexes

Schiff base (L) ligand is prepared via condensation of pyridine-2,6-dicarboxaldehyde with -2-aminopyridine. The ligand and its metal complexes are characterized based on elemental analysis, mass, IR, solid reflectance, magnetic moment, molar conductance, and thermal analyses (TG, DTG and DTA). The molar conductance reveals that all the metal chelates are non-electrolytes. IR spectra shows that L ligand behaves as neutral tridentate ligand and bind to the metal ions via the two azomethine N and pyridine N. From the magnetic and solid reflectance spectra, it is found that the geometrical structures of these complexes are octahedral (Cr(III), Fe(III), Co(II), Ni(II), Cu(II), and Th(IV)) and tetrahedral (Mn(II), Cd(II), Zn(II), and UO2(II)). 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*, ΔH*, ΔS* and ΔG* are calculated from the DTG curves using Coats-Redfern method. The synthesized ligand, in comparison to their metal complexes also was screened for its antibacterial activity against bacterial species, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus pyogones and Fungi (Candida). The activity data shows that the metal complexes to be more potent/antibacterial than the parent Schiff base ligand against one or more bacterial species.     

Redox, thermodynamic and spectroscopic of some transition metal complexes containing heterocyclic Schiff base ligands

Complexes of two series of Schiff base ligands, H₂L_a and H₂L_bderived from the reaction of 2,6-diacetyl pyridine with semicarbazide, H₂L_a and thiosemicarbazide, H₂L_b, with the metal ions, Co(II), Ni(II), Cu(II), VO(IV) and UO₂(VI) have been prepared. The ligands are characterized by elemental analysis, IR, UV–vis and ¹H NMR. The structures of the complexes are investigated with the IR, UV–vis, X-band ESR spectra, ¹H NMR and thermal gravimetric analysis as well as conductivity and magnetic moment measurements. The IR-spectra reveal the presence of variable modes of chelation for the investigated ligands. A variety of binuclear or mononuclear complexes were obtained with the two ligands in tri-, tetra or pentadentate forms. The bonding sites are the pyridine nitrogen, two azomethine nitrogen atoms and ketonic oxygen in case of H₂L_a or sulphur atoms in case of H₂L_b. The Coats–Redfern equation has been used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition steps of some complexes. Cyclic voltammograms of Co(II) and Ni(II) show quasi-reversible peaks. The redox properties and the nature of the electro-active species of the complexes have been characterized.     

Synthetic,spectroscopic and thermal studies of some complexes of unsymmetrical Schiff base ligand

New unsymmetrical Schiff base ligand (H₂L) is prepared via condensation of 2-hydroxy-5-methyl acetophenone, 2-hydroxy-5-chloro-3-nitro acetophenone and carbohydrazide in 1:1:1 ratio. Metal complexes of VO(IV), Cr(III), Mn(III), Fe(III), Zr(IV), MoO₂(VI), WO₂(VI) and UO₂(VI) have been prepared. These complexes were characterized by elemental analysis, UV–Vis and IR spectroscopy and magnetic moment and thermogravimetric analysis. The purity of the ligand and the metal complexes is confirmed by microanalyses, while unsymmetrical nature of ligand was further corroborated by ¹H NMR. All the complexes are air stable and insoluble in water and common organic solvents but fairly soluble in DMSO. The elemental analysis shows 1:1 metal to ligand stoichiometry for all the complexes. Thermal behaviour of the complexes was studied, the complexes were found to be quite stable and their thermal decomposition was generally via partially loss of the organic moiety and ended with respective metal oxide as a final product. Comparison of the IR spectrum of ligand and its metal complexes confirm that Schiff base behave as a dibasic tetradentate ligand towards the central metal ion with an ONNO donor sequence. The dc electrical conductivity is studied and data obtained obeyed the relation σ = σ ₀ exp(−E _a/kT) over the temperature range 40–130 °C. X-ray diffraction study of VO(IV) complex shows its crystalline nature with triclinic crystal system.     

Quinoxaline-based Schiff base transition metal complexes: review

The literature survey highlights spectra and biological activity of transition metal complexes derived from Schiff bases of quinoxaline. The extensive studies of synthesis, spectral, structural characterization, and biological activities of the metal complexes with heterocyclic Schiff bases of quinoxaline are reviewed.     

Synthesis and genotoxicity of Schiff base transition metal complexes

A new ONNO‐type azomethine ligand, 2,2′‐(ethane‐1,2‐diylidenedinitrilo)dibenzoic acid, (YLH₂) ( 1 ) has been prepared by the condensation of 2‐aminobenzoic acid and glyoxal. The coordination compounds [Ni(YL)] ( 2 ), [Co(YL)] ( 3 ), [Cu(YL)(H₂O)] ( 4 ), [Zn(YL)] ( 5 ), and [Cd(YL)] ( 6 ) of the YLH₂ ligand with five transition metal ions, Ni(II) Co(II), Cu(II), Zn(II), and Cd(II) have been prepared. The structures of these new azomethine compounds are proposed on the basis of the elemental analyses, proton nuclear magnetic resonance, infrared, ultraviolet–visible spectroscopy, and X‐ray powder diffraction patterns. Elemental analyses indicate a ligand metal ratio of 1:1 in the coordination compounds. X‐ray powder diffraction parameters for [Cu(YL)(H₂O)] and [Cd(YL)] compounds correspond to orthorhombic and monoclinic structures, respectively. The ligand acts as a tetradentate ligand bending through oxygen atoms of the hydroxyl groups of benzoic acid and nitrogen atoms of the azomethine groups. In addition, the ligand and its metal complexes have been studied for their possible genotoxic potential. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:119–130, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20665     

Derivatives of phosphate Schiff base transition metal complexes: synthesis, studies and biological activity

We report the synthesis and structural characterization of series of tetra- and hexacoordinate metal chelate complexes of phosphate Schiff base ligands having the general composition LMX(n).H(2)O and L(2)MX(n) (L=phosphate Schiff base ligand; M=Ag(+), Mn(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), or Fe(3+) and X=NO(3)(-), Br(-) or Cl(-)). The structure of the prepared compounds was investigated using elemental analysis, IR, 1H and 31P NMR, UV-vis, mass spectra, solid reflectance, magnetic susceptibility and conductance measurements as well as conductometric titration. In all the complexes studied, the ligands act as a chelate ligand with coordination involving the phosphate-O-atom and the azomethine-N-atom. IR, solid reflectance spectra and magnetic moment measurement are used to infer the structure and to illustrate the coordination capacity of ligand. IR spectra show the presence of coordinated nitrate and water molecule, the magnetic moments of all complexes show normal magnetic behavior and the electronic spectra of the metal complexes indicate a tetra- and octahedral structure for Mn(2+), octahedral structure of Fe(3+) and both square-planar and distorted octahedral structure for Cu(2+) complexes. Antimicrobial activity of the ligands and their complexes were tested using the disc diffusion method and the chosen strains include Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Microsporum canis, Trichophyton mentagrophyte and Trichophyton rubrum. Some known antibiotics are included for the sake of comparison and the chosen antibiotic are Amikacin, Doxycllin, Augmantin, Sulperazon, Unasyn, Septrin, Cefobid, Ampicillin, Nitrofurantion, Traivid and Erythromycin.     

Transition metal complexes of a Schiff base: synthesis,characterization, and antibacterial studies

Synthesis of a new Schiff base derived from 2-hydroxy-5-methylacetophenone and glycine and its coordination with compounds Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and UO₂(VI) are described. The ligand and complexes have been characterized on the basis of analytical, electrical conductance, infrared, ESR and electronic spectra, magnetic susceptibility measurements, and thermogravimetric analysis. The ligand is a dibasic tridentate (ONO) donor in all the complexes except Zn(II), where it is a monobasic bidentate (OO) donor. The solid state DC electrical conductivity of ligand and its complexes have been measured over 313–398 K, and the complexes were semiconducting. Antibacterial activities of ligand and its metal complexes have been determined by screening the compounds against various Gram (+) and Gram (?) bacterial strains.     

Synthesis, characterization and thermal properties of metal-containing polyurethane-ureas from hexadentate Schiff base metal complexes

Metal-containing polyurethane-ureas and copolyurethane-ureas have been synthesized by the reaction between hexadentate Schiff base metal complexes and isocyanate-terminated prepolymers. The metal complexes employed were MSal₂trien, where (M=Ni and Zn, Sal=salicylaldehyde and trien=triethylenetetramine). The NCO-terminated prepolymers used were tolylene 2,4-diisocyanate terminated poly(1,4-butanediol) (PB), tolylene 2,4-diisocyanate terminated poly(propylene glycol) (PP) prepolymers and the prepolymers synthesized from 4,4^′-diphenylmethane diisocyanate (MDI) and diols. The diols employed were polycaprolactone diol (PCL) and poly(tetramethylene oxide) (PTMO). Copolyurethane-ureas were synthesized by the reaction between MSal₂trien, PB or PP prepolymers and MDI. Characterizations of polymers were carried out using IR spectroscopy, elemental analysis, solubility and viscosity. Flammability of polymers was investigated by measuring limiting oxygen index (LOI) values and thermal stability was studied by thermogravimetric analysis (TGA).     

Spectroscopic and thermal characterization of biologically and anticancer active novel Schiff base metal complexes

The novel Schiff base ligand 2,2′-((1Z,1′Z)-(1,3-phenylenebis(azanylylidene))-bis(phenylmethanylylidene))dibenzoic acid (H₂L) was obtained by the condensation of m-phenylenediamine with o-benzoylbenzoic acid. The molecular and electronic structure of Schiff base ligand (H₂L) was optimized theoretically, and the quantum chemical parameters are calculated. Molecular docking was used to predict the binding between Schiff base ligand (H₂L) and the receptors of breast cancer mutant 3hb5-oxidoreductase, crystal structure E. coli (3t88) and crystal structure of S. aureus (3q8u). The newly synthesized Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) complexes were characterized by elemental microanalysis, molar conductance, spectroscopic techniques (IR, ¹H NMR, ESI-mass, ESR, UV–Vis), magnetic susceptibility, thermal (TG/DTG) and powder X-ray diffraction data to explicate their structures. The data showed that the complexes had composition of MH₂L type. The IR results confirmed the bidentate binding of the ligand involving two azomethine nitrogens. ¹H NMR spectral data of the ligand (H₂L) and its Zn(II) and Cd(II) complexes agreed well with the proposed structures. On the basis of electronic spectra and the magnetic measurements, octahedral geometry of the complexes was proposed. Thermogravimetric data (TG and DTG) were also studied. The kinetic and thermodynamic parameters for thermal decomposition of the complexes were calculated using the Coats–Redfern and Horowitz–Metzger methods. In order to appraise the effect of antimicrobial activity of metal ions upon chelation, the newly synthesized ligand and its metal complexes were screened against a number of bacteria organisms as Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Neisseria gonorrhoeae and against one fungus, Candida albicans, to assess their inhibiting potential by using the disc diffusion method. The results showed that in some cases the antimicrobial activity of complexes was more biologically active than the Schiff base ligand. Anticancer activity of the ligand and its metal complexes were evaluated in human cancer (MCF-7 cells viability). It was found that [Cd(H₂L)(H₂O)₂Cl₂]2H₂O complex showed lowest IC₅₀ than the others, and hence was the more active. The activity index was calculated.