Synthetic,characterization and catalytic studies of some coordination compounds derived from unsymmetrical quadridentate Schiff base ligand

The stable complexes of VO(IV), Cr(III), Mn(III), Fe(III), MoO₂(VI), and WO₂(VI), with an unsymmetrical tetradentate Schiff base ligand derived from 2-hydroxy-5-methylacetophenone, 2-hydroxy-5-chloroacetophenone and carbohydrazide were synthesized and characterized by the elemental analysis, UV-Vis and IR spectroscopy, magnetic measurements and thermal analysis. The VO(IV) and Mn(III) complexes were tested for the catalytic oxidation of styrene. The conversion of styrene increases with use of VO(IV) catalyst and decreases with use of Mn(III) catalyst.     

Synthesis, molecular modeling, thermal and spectral studies of metal complexes of hydrazone derived from 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione and thiosemicarbazide

Metal complexes with the general formula [ML(H2O)(CH3OH)x]·nH2O·(CH3OH)y(NO3)z [M=Cu(II), Ni(II), Co(II), VO(IV), Cr(III), Cd(II), Zn(II) or UO2(VI); x=0-2; y=0,1; z=0,1; n=0-2, 6 and L=hydrazone (H2L) derived from condensation of thiosemicarbazide with 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione. The synthesized ligand and its metal complexes have been characterized on the basis of elemental analyses, spectral and magnetic studies as well as thermal gravimetric analysis (TGA). The deprotonated ligand acts as a dibasic tridentate (ONS) via phenolate oxygen, azomethine (CN), and thiolate (C-S) groups. Copper(II) complex exhibits square planar geometry. Nickel(II), chromium(III) and dioxouranium(VI) complexes exhibit octahedral geometry. Cobalt(II), cadmium(II) and zinc(II) complexes showed tetrahedral geometry, whereas oxovanadium(IV) reveals square pyramidal geometry. Thermal analysis are investigated and showed either three or four thermal decomposition steps. Kinetic parameters (Ea, A, ΔH, ΔS and ΔG) of the thermal decomposition stages have been evaluated using Coats-Redfern equations. The molecular parameters of the ligand and its metal complexes have been calculated and correlated with the experimental data such as IR and TGA results.     

Synthesis,characterization, magnetic,thermal and electrochemical studies of oxidovanadium (IV) picolyl hydrazones as functional catechol oxidase models

The picolyl hydrazone ligands derived from picolonic acid hydrazide and α-pyridyle ketone (L¹, L² and L³), α-acetyl thiophene (L⁴), α-formyl or α-acetyl phenol (L⁵ and L⁶ respectively) and 2-hydroxy-1-naphthaldehyde (L⁷) react with equimolecular amount of vanadyl sulfate in refluxing methanol to yield oxidovanadium (IV) complexes. The structure of the obtained ligands and their oxidovanadium (IV) complexes were characterized by various physicochemical techniques, viz. elemental analysis, molar conductance, magnetic susceptibility measurements, thermal analysis (TGA & DTG), IR, electronic absorption and ESR spectral studies. Cyclic voltammeteric behavior of the complexes has also been discussed. Five-coordinate square-pyramidal structure was proposed for all complexes. A monomeric nature was reported for complexes (2), (3), (6), and (7), while dimeric structures were suggested for complexes (1), (4) and (5). The ability of the complexes to catalyze the aerobic oxidation of catechol to the light absorbing o-quinone has been investigated. The results obtained show that all complexes catalyze this oxidation reaction and large variations in the rate were observed. Electrochemical data for most complexes show that there is a linear relationship between their ability to oxidize catechole and their E_1/2 potentials. The most effective catalysts were those complexes which exhibited E_1/2 values approached to the E° value of the natural tyrosinase enzyme isolated from mushroom, while those that largely deviated from that potential exhibited lower oxidase catalytic activity. The probable mechanistic implications of the catalytic oxidation reactions are discussed.     

Conventional and microwave synthesis,spectral, thermal and antimicrobial studies of some transition metal complexes containing 2-amino-5-methylthiazole moiety

Schiff base metal complexes of Cr(III), Co(II), Ni(II) and Cu(II) derived from 5-chlorosalicylidene-2-amino-5-methylthiazole (HL¹) and 2-hydroxy-1-naphthylidene-2-amino-5-methylthiazole (HL²) have been synthesized by conventional as well as microwave methods. These compounds have been characterized by elemental analysis, FT-IR, FAB-mass, molar conductance, electronic spectra, ¹H-NMR, ESR, magnetic susceptibility, thermal, electrical conductivity and XRD analyses. The complexes exhibit coordination number 4 or 6. The complexes are coloured and stable in air. Analytical data reveal that all the complexes exhibit 1:2 (metal:ligand) ratio. IR data show that the ligand coordinates with the metal ions in a bidentate manner through the phenolic oxygen and azomethine nitrogen. FAB-mass and thermal data show degradation pattern of the complexes. The thermal behaviour of metal complexes shows that the hydrated complexes lose water molecules of hydration in the first step; followed by decomposition of ligand molecules in the subsequent steps. XRD patterns indicate crystalline nature for the complexes. The Schiff bases and metal complexes show good activity against the Gram-positive bacteria; Staphylococcus aureus and Gram-negative bacteria; Escherichia coli and fungi Aspergillus niger and Candida albicans. The antimicrobial results also indicate that the metal complexes are better antimicrobial agents as compared to the Schiff bases.     

Synthesis and magnetic,spectral and thermal eukaryotic DNA studies of some 2-acetylpyridine- [N-(3-hydroxy-2-naphthoyl)] hydrazone complexes

Complexes of Ni(II), Co(II), Cu(II), Zn(II), Cd(II), Hg(II) and U(VI)O₂ with 2-acetylpyridine-[N-(3-hydroxy-2-naphthoyl)] hydrazone (H₂APHNH) have been prepared and characterized by elemental analysis, molar conductance, thermal (TG, DTG), spectral (¹H NMR, IR, UV–Vis, ESR) and magnetic measurements. ¹H NMR spectrum of the ligand suggests the presence of intramolecular hydrogen bonding. IR spectra show that H₂APHNH is a bidentate, tridentate and/or tetradentate ligand. Thermal decomposition of some complexes ended with metal oxide as a final product. ESR spectra gave evidence for the proposed structure and the bonding for some Cu(II) complexes. Biological activity measurements were carried out.     

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.     

Synthesis,characterization, and biological activity of metal complexes of azohydrazone ligand

A new azohydrazone, 2-hydroxy-N′-2-hydroxy-5-(phenyldiazenyl)benzohydrazide (H₃L) and its copper(II), nickel(II), cobalt(II), manganese(II), zinc(II), cadmium(II), mercury(II), vanadyl(II), uranyl(II), iron(III), and ruthenium(III) complexes have been prepared and characterized by elemental and thermal analyses as well as spectroscopic techniques (¹H-NMR, IR, UV-Vis, ESR), magnetic, and conductivity measurements. Spectral data showed a neutral bidentate, monobasic bidentate, monobasic tridentate, and dibasic tridentate bonding to metal ions via the carbonyl oxygen in ketonic or enolic form, azomethine nitrogen, and/or deprotonated phenolic hydroxyl oxygen. ESR spectra of solid vanadyl(II) complex (2), copper(II) complexes (3–5), and (7) and manganese(II) complex (10) at room temperature show isotropic spectra, while copper(II) complex (6) shows axial symmetry with covalent character. Biological results show that the ligand is biologically inactive but the complexes exhibit mild effect on Gram positive bacteria (Bacillus subtilis), some octahedral complexes exhibit moderate effect on Gram negative bacteria (Escherichia coli), and VO(II), Cd(II), UO(II), and Hg(II) complexes show higher effect on Fungus (Aspergillus niger). When compared to previous results, metal complexes of this hydrazone have a mild effect on microorganisms due to the presence of the azo group.     

Synthesis,spectral, and thermal studies of oxomolybdenum(V) Schiff-base complexes derived from heterocyclic β-diketone

Six mononuclear Mo(V) Schiff-base complexes were prepared by the reaction of MoCl₅ with Schiff bases, namely HL¹–HL³ and HL⁴–HL⁶, such as 5-hydroxy-3-methyl-1(2-chloro)phenyl-1H-pyrazolone-4-carbaldehyde (I), 5-hydroxy-3-methyl-1(3-chloro)phenyl-1H-pyrazolone-4-carbaldehyde (II), and 5-hydroxy-3-methyl-1(3-sulfoamido)phenyl-1H-pyrazolone-4-carbaldehyde (III) with ethanolamine and propanolamine, respectively, in aqueous ethanolic medium. The resulting complexes have been characterized by elemental analyses, molar conductance, FT-IR, ¹H-NMR, electronic, electron spin resonance (ESR) spectra, magnetic susceptibility, and thermal study. The molar conductivity data show them to be non-electrolytes. IR and ¹H-NMR spectral data suggest that the ligand is a dibasic bidentate with ON donor toward metal ion. Electronic, magnetic, and ESR spectral data suggest that the oxomolybdenum(V) complexes have distorted octahedral geometry. One chloride coordinated to molybdenum is confirmed by thermal study.     

Zeolite-Y enslaved manganese(III) complexes as heterogeneous catalysts

Traditional catalytic procedures for oxidation of phenol produce environmentally undesirable wastes. As a consequence, there is a clear demand for development of an environmentally benign catalytic route for the selective oxidation of phenol. A series of zeolite-Y enslaved Mn(III) complexes with Schiff bases derived from vanillin furoic-2-carboxylic acid hydrazone (VFCH), vanillin thiophene-2-carboxylic acid hydrazone (VTCH), ethylvanillin thiophene-2-carboxylic acid hydrazone (EVTCH), and/or ethylvanillin furoic-2-carboxylic acid hydrazone have been synthesized and characterized by physico-chemical techniques. Catalytic oxidations of phenol using 30% H₂O₂ as an oxidant over [Mn(VTCH)₂·2H₂O]⁺-Y, [Mn(VFCH)₂·2H₂O]⁺-Y, and [Mn(EVTCH)₂·2H₂O]⁺-Y under mild conditions were studied. These zeolite-Y enslaved Mn(III) complexes are stable and recyclable under current reaction conditions.     

Synthesis,spectral and EPR studies of oxovanadium(IV) complexes incorporating tridentate ONO donor hydrazone ligands: Structural study of one oxovanadium(V) complex

Five oxovanadium(IV) complexes of 2-hydroxy-4-methoxybenzaldehyde nicotinic acid hydrazone (H₂L¹), 2-hydroxy-4-methoxyacetophenone nicotinic acid hydrazone (H₂L²) and a binuclear oxovanadium(V) complex of H₂L² have been synthesized. These complexes were characterized by different physicochemical techniques like electronic, infrared and EPR spectral studies. The complexes [VOL¹]₂ · H₂O (1) and [VOL²]₂ · H₂O (4) are binuclear and [VOL¹bipy] (2), [VOL¹phen] · 1.5H₂O (3) and [VOL²phen] · 2H₂O (6) are heterocyclic base adducts and are EPR active. In frozen DMF at 77 K, all the oxovanadium(IV) complexes show axial anisotropy with two sets of eight line patterns. The complex [VOL² · OCH₃]₂ (5) is an unusual product and has distorted octahedral geometry, as obtained by X-ray diffraction studies.     

Carbohydrazone polychelates: Synthesis,physicochemical characterization,solid state conductance and biological studies

The polychelates of Ti(III), VO(IV), Cr(III), Mn(III), Fe(III), Zr(IV), MoO₂(VI) and UO₂(VI) with the chelating hydrazone derived from 2,4-dihydroxy-5-acetylacetophenone and carbohydrazide have been synthesized. The polychelates have been characterized on the basis of elemental analyses, IR, magnetic moment, electronic spectral data and thermal analysis. Various kinetic parameters have been determined from the thermal data and decomposition follows first order kinetics. The solid—state electrical conductivity has been measured over 40–130°C-temperature range and all the compounds showed semiconducting behavior as their conductivity increases with increase in temperature. The ligand and its polychelates have also been screened for their antimicrobial activities using various microorganisms and all of them were found to be active against the organisms.     

Crystal Structure of 2-[2-hydroxy-3-methoxyphenyl]-3-[2-hydroxy-3-methoxybenzylamino]-1,2-dihydroquinazolin-4(3H)-one and the Synthesis, Spectral and Thermal Investigation of its Transition Metal Complexes

A new 1,2-dihydroquinazolin-4(3H)-one ligand, 2-[2-hydroxy-3-methoxyphenyl]-3-[2-hydroxy-3-methoxybenzylamino]-1,2-dihydroquinazolin-4(3H)-one (Hmpbaq), formed by the condensation of 2-aminobenzoylhydrazide with 2-hydroxy-3-methoxybenzaldehyde and its copper(II), nickel(II), cobalt(II), manganese(II), zinc(II) and cadmium(II) complexes, have been synthesized. Their structures have been elucidated on the basis of elemental analyses, conductance measurements, magnetic moments, spectral (i.r., ¹H-n.m.r., u.v.–vis., e.p.r. and FAB-mass) and thermal studies. The formation of 1,2-dihydroquinazolin-4(3H)-one rather than hydrazone in the reaction of 2-aminobenzoylhydrazide with 2-hydroxy-3-methoxybenzaldehyde is confirmed by the ¹H-n.m.r. spectra and single crystal X-ray diffraction studies. The tridentate behavior of the ligand was proposed on the basis of spectral studies. X-band e.p.r. spectra of the copper(II) and manganese(II) complexes in the polycrystalline state at room temperature and liquid nitrogen temperature were recorded and their salient features are reported. Thermal stabilities of the manganese(II) and zinc(II) complexes have been studied.     

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.     

pH-metric studies on formation constants of the complexes of substituted pyrazoles with some lanthanide metal ions and the influence of ionic strengths on complex equilibria in a 70% dioxane-water mixture

The pK a values of N-heterocyclic compounds (substituted pyrazoles) in a 70% (v/v) dioxane-water mixture have been determined using pH-metric measurements. The stability constants of the complexes of Dy(III), Nd(III), Sm(III), and Tb(III) with 3-(2-hydroxyphenyl)-5-methylpyrazole, l-phenyl-3-(2-hydimyphenyl)-5-methylpyrazole 3-(2-hydroxy-4-methylphenyl)-5-methylpyrazole, and l-phenyl-3-(2-hydroxy-4-methylphenyl)-5-methylpyrazole have been determined by the pH-metric method at ( 300 ± 0.1) K. The effect of ionic strengths on the complexes of Sm³⁺ and Pr³⁺ ions with pyrazole has been investigated in the internal from 0.02 to 0.1 mol dm⁻³ (sodium perchlorate) in the pH range 2–3.     

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.     

Diorganotin(IV) complexes with furan-2-carbohydrazone derivatives: synthesis,characterization, crystal structure and antibacterial activity

Four new diorganotin(IV) complexes, R₂SnL (L?=?L^a: R?=?Me 1, Ph 2; L?=?L^b: R?=?Me 3, and Ph 4), have been synthesized by reaction of hydrazone ONO donors, 5-bromo-2-hydroxybenzaldehyde furan-2-carbohydrazone (H₂L^a) and 2-hydroxynaphthaldehyde furan-2-carbohydrazone (H₂L^b) with diorganotin(IV) dichloride in the presence of a base. The compounds have been investigated by elemental analysis and IR, ¹H NMR, and ¹¹⁹Sn NMR spectroscopies. Spectroscopic studies show that the hydrazone is a tridentate dianionic ligand, coordinating via the imine nitrogen and phenolic and enolic oxygens. The structures of H₂L^b and 3 have also been confirmed by X-ray crystallography. The results show that the structure of 3 is a distorted square pyramid with imine nitrogen in apical position. The in vitro antibacterial activities of ligands and complexes have been evaluated against gram-positive (Bacillus cereus and Staphylococcus aureus) and gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. H₂L^a and H₂L^b show no activity but the diphenyltin(IV) complexes exhibit good activities towards two bacterial strains in comparison with standard bacterial drugs.     

Synthesis, characterization and antimicrobial activity of 3d transition metal complexes of a biambidentate ligand containing quinoxaline moiety

A new series of oxovanadium(IV), chromium(III), manganese(II), iron(III), cobalt(II), nickel(II), and copper(II) complexes of the 3-hydrazino quinoxaline-2-one (HQO) were prepared and characterized. The ligand exhibits biambidenticity. It behaves as a bidentate ON donor in oxovanadium(IV), iron(III) and copper(II) complexes and as a bis bidentate ONNN donor in chromium(III), manganese(II), cobalt(II) and nickel(II) complexes. The nature of bonding and the stereochemistry of the complexes have been deduced from elemental analyses, thermal, infrared, ¹H NMR, electronic spectra, magnetic susceptibility and conductivity measurements. An octahedral geometry was suggested for all the complexes. All the complexes show subnormal magnetic moments. The ligand, HQO, and its complexes were tested against one strain Gram +ve bacteria (Staphylococcus aureus), Gram −ve bacteria (Escherichia coli). The prepared metal complexes exhibited higher antimicrobial activities than the parent ligand.     

Synthesis of stannic(IV) complexes: Their structural elucidation in solid and solution state and antimicrobial activity

A series of organotin(IV) thiocarboxylates have been synthesized with the general formula R₂SnL₂ and R₃SnL (R = Ph₂(I), Me₃(II), n‐Bu₃(III), Ph₃(IV), Cy₃(V), Me₂(VI), n‐Bu₂(VII), and L = piperidine‐1‐thiocarboxylic acid) in anhydrous toluene under the reflux conditions. The complexes were characterized by microanalysis, IR, ¹H and ¹³C NMR, mass spectrometry, and XRD. NMR data revealed that thiocarboxylic acid acts as bidentate, and complexes exhibit the four‐coordinated geometry in solution state. In solid state, diorganotin complexes exhibit the hexa‐coordinated geometry whereas the triorganotin(IV) compounds show the five‐coordinated geometry. These complexes were also tested for their antimicrobial activity along with the ligand against different animals, plant pathogens, and Artemia salina. All complexes with few exceptions show high activity as compared to the ligand. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:664–674, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20380     

Synthesis and characterization of some Cr(III), Fe(III) and Zr(IV) compounds with substituted o-hydroxy benzophenone

This work presents our data concerning the synthesis and characterization of some Cr(III), Fe(III) and Zr(IV) complexes with substituted (2-hydroxy-4-methoxy-phenyl)-phenyl-methanone - C₁₄H₁₂O₃, denoted by (L1). The synthesis of these complex compounds was performed using melted urea as reaction medium. The obtained complexes have been studied by chemical analysis, IR spectroscopy, X-ray diffraction and thermogravimetric analysis. Based on the data resulting from the thermal behaviour of the studied complex compounds, the kinetic parameters of the thermal decomposition reactions have been determined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spectral and thermal studies of alloxan complexes

The complexes of alloxan with Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) Cd(II), Hg(II), Ti(IV) and Zr(II) have been isolated and characterized on the basis of elemental analysis, molar conductivity, spectral studies (mid infrared, ¹H-NMR and UV/vis spectra), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The thermal decomposition of the metal complexes was studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The kinetic thermodynamic parameters, E*, ΔH*, ΔS* and ΔG*, were calculated using Coats and Redfern and Horowitz and Metzger equations. The ligand and its complexes have been studied for possible biological activity including antibacterial and antifungal activity.