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 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.     

Spectral, magnetic, thermal, antimicrobial, and eukaryotic DNA studies on acetone [N-(3-hydroxy-2-naphthoyl)]hydrazone complexes

Abstract  

Acetone [N-(3-hydroxy-2-naphthoyl)] hydrazone (H₂AHNH) has been prepared and its structure confirmed by elemental analysis and ¹H NMR spectroscopy. It has been used to produce diverse complexes with Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and U(VI)O₂ ions. The complexes obtained have been investigated by thermal analysis, spectral studies (¹H NMR, IR, UV–visible, ESR), and magnetic measurements. IR spectra suggest that H₂AHNH acts as a bidentate ligand. The electronic spectra of the complexes and their magnetic moments provide information about geometries. The ESR spectra give evidence for the proposed structure and the bonding for some Cu(II) complexes. Thermal decomposition of the Ni(II) and Cu(II) complexes afforded metal oxides as final products. Kinetic data were obtained for each stage of thermal degradation of some of the complexes using the Coats–Redfern method. The formation of complexes in solution was studied pH-metrically and the order of their stability constants (log K) was found to be U(VI)O₂ > Cu(II) > Zn(II) > Ni(II) > Cd(II) > Co(II). Antimicrobial and eukaryotic DNA studies were carried out.     

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, electrical conductivity,and catalytic studies of some coordination polymers of salen-type schiff base

Coordination polymers of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) with the salen-type Schiff base 4,4′-bis[(N-ethanesalicylaldehydediamine-5)azo]biphenyl have been prepared and characterized by elemental analyses, IR and electronic spectra, magnetic susceptibility measurements, and thermogravimetric analysis. Thermogravimetric analysis confirms the coordination of H₂O in complexes. The ¹H NMR spectrum of ligand clearly indicates the presence of OH and azomethine groups. The octahedral geometry have been suggested for Mn(II), Fe(II), Co(II), and Ni(II) complexes, and square planar Cu((II), whereas tetrahedral is suggested for Zn(II) and Cd(II) polychelates. Thermal data have been analyzed for kinetic parameters by both Coat-Redfern and Broido methods. Solid-state dc conductivity of ligand and its polychelates was measured in their compressed pellet form over 313–413 K temperature range. Solidstate conductivity lies in the range 4.361 × 10⁻¹¹ to 7.241 × 10⁻¹⁰ Ohm⁻¹ cm⁻¹ indicating their semiconducting behavior. Oxidation of styrene with selected catalysts was tested using H₂O₂ as an oxidant.     

Metal chelates of salicyl-4-aminoantipyrine

The formation constants of salicyl-4-amino-2,3-dimethyl-1-phenyl-3-pyrazoline-5-one (SAAP) complexes with 3d transition metal ions [Cu(II), Ni(II), Co(II), Zn(II) and Mn(II)] have been determined in 60% ethanol-water medium ofμ = 0.1M (NaCl) at 25°C. It is observed that the formation constants for chelates with 3d transition metals follow the order Mn(II) < Co(II) < Ni(II) < Zn(II) < Cu(II). The effects of metal ions, ionic radii, electronegativities and ionization potentials on chelate formation constants are discussed. Complexes of UO₂(II) and Pd(II) have been synthesized and characterised by elemental analysis, electrolytic conductance, IR spectra and magnetic measurements. The ligand forms the complexes PdLCl and UO₂L₂,2H₂O, where L is a uninegatively charged tridentate ligand (ONO donor sets).     

Molecular structure,molecular docking,thermal, spectroscopic and biological activity studies of bis‐Schiff base ligand and its metal complexes

Coordination compounds of Fe(III), Zn(II), Ni(II), Co(II), Cu(II), Cd(II) and Mn(II) ions were synthesized from the ligand [4,4′‐((((ethane‐1,2‐diylbis(oxy))bis(2,1‐phenylene))bis(methanylylidene))bis(azanylylidene))diphenol]ethane (H₂L) derived from the condensation of bisaldehyde and 4‐aminophenol. Microanalysis, magnetic susceptibility, infrared, ¹H NMR and mass spectroscopies, molar conductance, X ray powder diffraction and thermal analysis were used to confirm the structure of the synthesized chelates. According to the data obtained, the composition of the 1:1 metal ion–bis‐Schiff base ligand was found to be [M(H₂L)(H₂O)₂]Cl_n (M = Zn(II), Ni(II), Co(II), Cu(II), Cd(II) and Mn(II), n = 2; Fe(III), n = 3). Magnetic susceptibility measurements and reflectance spectra suggested an octahedral geometry for the complexes. Central metals ions and bis‐Schiff base coordinated together via O2 and N2 donor sites which as evident from infrared spectra. The Gaussian09 program was applied to optimize the structural formula for the investigated Schiff base ligand. The energy gaps and other important theoretical parameters were calculated applying the DFT/B3LYP method. Molecular docking using AutoDock tools was utilized to explain the experimental behaviour of the Schiff base ligand towards proteins of Bacillus subtilis (5 h67), Escherichia coli (3 t88), Proteus vulgaris (5i39) and Staphylococcus aureus (3ty7) microorganisms through theoretical calculations. The docked protein receptors were investigated and the energies of hydrogen bonding were calculated. These complexes were then subjected to in vitro antibacterial studies against several organisms, both Gram negative (P. vulgaris and E. coli) and Gram positive (S. pyogones and B. subtilis). The ligand and metal complexes exhibited good microbial activity against the Gram‐positive and Gram‐negative bacteria.     

Spectral,magnetic, thermal,antimicrobial, and eukaryotic DNA studies on acetone [<Emphasis Type="Italic">N</Emphasis>-(3-hydroxy-2-naphthoyl)]hydrazone complexes

Abstract  Acetone [N-(3-hydroxy-2-naphthoyl)] hydrazone (H₂AHNH) has been prepared and its structure confirmed by elemental analysis and ¹H NMR spectroscopy. It has been used to produce diverse complexes with Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and U(VI)O₂ ions. The complexes obtained have been investigated by thermal analysis, spectral studies (¹H NMR, IR, UV–visible, ESR), and magnetic measurements. IR spectra suggest that H₂AHNH acts as a bidentate ligand. The electronic spectra of the complexes and their magnetic moments provide information about geometries. The ESR spectra give evidence for the proposed structure and the bonding for some Cu(II) complexes. Thermal decomposition of the Ni(II) and Cu(II) complexes afforded metal oxides as final products. Kinetic data were obtained for each stage of thermal degradation of some of the complexes using the Coats–Redfern method. The formation of complexes in solution was studied pH-metrically and the order of their stability constants (log K) was found to be U(VI)O₂ > Cu(II) > Zn(II) > Ni(II) > Cd(II) > Co(II). Antimicrobial and eukaryotic DNA studies were carried out. Graphical abstract        

Synthesis,characterization and antimicrobial studies of novel ONO donor hydrazone Schiff base complexes with some divalent metal (II) ions

Metal complexes of two general formulae [M(L)(Cl)(H₂O)₂] [M = Mn(II), Co(II), Ni(II) and Cu(II)] and [M(L)(H₂O)] [M = Zn(II) and Cd(II)] with pyrazine-2-carbohydrazone of 2-hydroxy-5-methylacetophenone (H₂L) are synthesized and characterized by microanalytical, thermal, magnetic susceptibility measurement, spectroscopic (IR, ¹H NMR, ¹³C NMR), mass, molar conductance, X-ray powder diffraction, ESR and SEM studies. While the molar conductance measurements in DMSO indicated their non-electrolytic nature, the spectroscopic studies confirmed a tridentate ONO donor behaviour of the ligand towards the central metal ion. Based on the physico-chemical studies monomeric octahedral geometry around Mn(II), Co(II), Ni(II) and Cu(II) ions (i.e. for the first series of complexes) whereas tetrahedral to Zn(II) and Cd(II) ions (i.e. for the second series of complexes) are suggested. Based on the thermal behavior of the complexes, various kinetic and thermodynamic parameters were evaluated using Coats-Redfern method. The ligand and its metal complexes were screened for in vitro antibacterial and antifungal activity against Gram +ve S. aureus, B. subtilis and Gram –ve E. coli and S. typhi. and fungal strains, C. albicans and A. niger. The observed data infer promising biological activity of some of these complexes compared the parent ligand against all bacterial and fungal species.     

Synthesis,spectral, and antifungal studies of transition metal complexes with sixteen-membered hexadentate macrocylic ligand

A novel hexadentate nitrogen donor [N₆] macrocyclic ligand viz, 1,5,11,15,21,22-hexaaza-2,14-dimethyl-l4,12-diphenyltricyclo[15.3.1.I(7–11)]docosane[1,4,6,8,10(22)-11,14,16,18,20(21)]decaene (L), has been synthesised. The Co (II), Ni (II), and Cu (II) complexes with this ligand have been prepared and subjected to elemental analysis, molar conductance, magnetic susceptibility measurements, mass, ¹H NMR (ligand), IR, electronic, and ESR spectral studies and electrochemical investigation. On the basis of molar conductance the complexes can be formulated as [M(L)]X₂ (where M = Co (II), Ni (II), Cu (II) and X = Cl⁻ and NO₃⁻) due to their 1: 2 electrolytic nature in DMSO. All the complexes are of the high-spin type and are six-coordinated. On the basis of IR, electronic, and ESR spectral studies, an octahedral geometry has been assigned for the Co(II) and Ni(II) complexes, whereas a tetragonal geometry for the Cu(II) complexes was found. Antimicrobial activity of L and its complexes as growth inhibiting agents have been screened in vitro against two species (F. moniliformae and R. solani) of plant pathogenic fungi. The text was submitted by the authors in English.     

Geometric parameters and energies of molecular structures of macrocyclic metal chelates in the ternary 3<Emphasis Type="Italic">d</Emphasis> M(II) ion-ethanedithioamide-ethanedial systems according to quantum-chemical DFT B3LYP calculations

The thermodynamic and geometric parameters of isomeric macrotricyclic Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes with the (NSSN) coordination of the ligand donor centers formed in the reaction of corresponding hexacyanoferrates(II) with ethanedithioamide H₂N-C(=S)-C(=S)-NH₂ and ethanedial HC(=O)-CH(=O) in gelatin-immobilized matrix implants have been calculated by the hybrid B3LYP density functional theory method with the use of the 6–31G(d) basis set and the Gaussian 03 program package. The bond lengths and bond and torsion angles in these complexes have been reported, and it has been stated that the Mn(II), Co(II), and Cu(II) complexes are nearly planar, the Fe(II) and Ni(II) complexes are slightly nonplanar, while the Zn(II) complex exhibits a rather considerable deviation from coplanarity. The additional five-membered chelate ring resulting from template cross-linking is almost planar in all cases.     

Novel Schiff base ligand and its metal complexes with some transition elements. Synthesis,spectroscopic, thermal analysis,antimicrobial and in vitro anticancer activity

A novel Schiff base ligand (H₂L) was prepared through condensation of 2,6‐diaminopyridine and o‐benzoylbenzoic acid in a 1:2 ratio. This Schiff base ligand was characterized using elemental and spectroscopic analyses. A new series of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) metal complexes of H₂L were prepared and characterized using elemental analysis, spectroscopy (¹H NMR, mass, UV–visible, Fourier transform infrared, electron spin resonance), magnetic susceptibility, molar conductivity, X‐ray powder diffraction and thermal analysis. The complexes are found to have trigonal bipyramidal geometry except Cr(III), Mn(II) and Fe(III) complexes which have octahedral geometry based on magnetic moment and solid reflectance measurements. The infrared spectral studies reveal that H₂L behaves as a neutral bidentate ligand and coordinates to the metal ions via the two azomethine nitrogens. ¹H NMR spectra confirm the non‐involvement of the carboxylic COOH proton in complex formation. The presence of water molecules in all reported complexes is supported by thermogravimetric studies. Kinetic and thermodynamic parameters were determined using Coats–Redfern and Horowitz–Metzger equations. The synthesized ligand and its complexes were screened for antimicrobial activities against two Gram‐positive bacteria (Bacillus subtilis and Staphylococcus aureus), two Gram‐negative bacteria (Escherichia coli and Neisseria gonorrhoeae) and one fungus (Candida albicans). Anticancer activities of the ligand and its metal complexes against human breast cancer cell line (MCF7) were investigated. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis, electrochemical and structural characterization of novel azacrown ether containing macrocyclic redox-active vic-dioxime ligand and its mononuclear transition metal complexes: Application of DEPT, HSQC, HMBC-NMR and cyclic voltammetry

This paper presents a new azacrown containing vic-dioxime; anti-N-(4-aminophenyl)aza-15-crown-5-glyoxime (LH₂), and its mononuclear nickel(II), copper(II), cobalt(II), cadmium(II) and zinc(II) complexes. The azacrown moieties appended at the periphery of the oxime provide solubility for the vic-dioxime ligand and complexes in common organic solvents. The mononuclear M(LH)₂ (M = Ni and Cu), M(LH)₂(H₂O)₂ (M = Co) and [M(LH)(H₂O)(Cl)] (M = Cd and Zn) complexes have been obtained with the metal:ligand ratios of 1:2 and 1:1. The structure of the ligand is confirmed by elemental analysis, Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis), mass spectrometry (MS), one-dimensional (1D) ¹H, ¹³C NMR, distortionless enhancement by polarization transfer (DEPT) and two-dimensional (2D) heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) techniques. The structures of the complexes are confirmed by elemental analyses, MS, UV-Vis, FT-IR and ¹H, ¹³C NMR techniques. Redox behaviors of the ligand and its complexes have been investigated by cyclic voltammetry at the glassy carbon electrode in 0.1 M TBATFB in DMSO. The antibacterial activity was studied against Staphylococcus aureus ATCC 29213, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Lactobacillus acidophilus RSHM 06029, Escherichia coli ATCC 25922, Pseudomonasaeruginosa ATCC 27853. The antimicrobial test results indicate that all the complexes have low levels of antibacterial activity against both Gram negative and Gram positive bacterial species.     

Physicochemical characterization of nanobidentate ferrocene‐based Schiff base ligand and its coordination complexes: Antimicrobial,anticancer, density functional theory,and molecular operating environment studies

A novel bidentate Schiff base ligand (HL, Nanobidentate Ferrocene based Schiff base ligand L (has one replaceable proton H)) was prepared via the condensation of 2‐amino phenol with 2‐acetyl ferrocene. The ligand was characterized using elemental analysis, mass spectrometry, infrared (IR) spectroscopy, ¹proton nuclear magnetic resonance (H‐NMR) spectroscopy, scanning electron microscopy (SEM), and thermal analysis. The corresponding 1:1 metal complexes with some transition‐metal ions were additionally characterized by their elemental analysis, molar conductance, SEM, and thermogravimetric ana1ysis (TGA). The complexes had the general formula [M(L)(Cl)(H₂O)₃]xCl·nH₂O (M = Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II)), (x = 0 for Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II), x = 1 for Cr(III) and Fe(III)), (n = 1 for Cr(III), n = 3 for Mn(II) and Co(II), n = 4 for Fe(III), Ni(II), Cu(II), Zn(II), and Cd(II)). Density functional theory calculations on the HL ligand were also carried out in order to clarify molecular structures by the B31YP exchange‐correlation function. The results were subjected to molecular orbital diagram, highest occupied mo1ecu1ar orbital–lowest occupied molecular orbital, and molecular electrostatic potential calculations. The parent Schiff base and its eight metal complexes were assayed against four bacterial species (two Gram‐negative and two‐Gram positive) and four different antifungal species. The HL ligand was docked using molecular operating environment 2008 with crystal structures of oxidoreductase (1CX2), protein phosphatase of the fungus Candida albicans (5JPE), Gram(?) bacteria Escherichia coli (3T88), Gram(+) bacteria Staphylococcus aureus (3Q8U), and an androgen‐independent receptor of prostate cancer (1GS4). In order to assess cytotoxic nature of the prepared HL ligand and its complexes, the compounds were screened against the Michigan cancer foundation (MCF)‐7 breast cancer cell line, and the IC₅₀ values of compounds were calculated.     

Spectroscopic and thermodynamic studies of complexation of some divalent metal ions with isatin-<Emphasis Type="Italic">β</Emphasis>-thiosemicarbazone

Metal complexes of some divalent metal ions (Co, Ni, Cu, Zn, Hg, and Pd) with isatin-β-thiosemicarbazone (ITS) as the Schiff base have been investigated potentiometrically and spectrophotometrically. The dissociation constants of the ligand and formation constants of the metal complexes, as well as the corresponding thermodynamic functions (ΔG, ΔH and ΔS) have been determined at different temperatures in ethanol—water solution. The full stability constants were also evaluated spectrophotometrically by the Job method. The experimental results indicate that Cu(II), Zn(II), Pd(II), and Hg(II) form one-to-one molecular complexes (ML) with the studied ligand, whereas Co(II) and Ni(II) form both ML and ML₂ species.     

Synthesis,characterization and in vitro antimicrobial and anti‐breast cancer activity studies of metal complexes of novel pentadentate azo dye ligand

A new azo dye with N3O2 donor set of atoms has been synthesized via coupling reaction of 2,6‐diaminopyridine with p‐methoxybenzaldehyde. The molecular and electronic structure of the azo dye ligand (L) was optimized theoretically and the quantum chemical parameters were calculated. Molecular docking was used to predict the binding between L and the receptors of breast cancer mutant 3hb5‐oxidoreductase, crystal structure of Escherichia coli (3 T88) and crystal structure of Staphylococcus aureus (3q8u). The newly synthesized L was used for complex formation with Cr(III), Mn(II), Fe(III), Co.(II), Ni(II), Cu(II), Zn(II) and Cd(II) ions. The nature of bonding and the stoichiometry of L and its mononuclear complexes were deduced from elemental analyses, spectroscopic, magnetic susceptibility, molar conductance, electron spin resonance and conductivity measurements, thermogravimetric analyses and powder X‐ray diffraction. Elemental analysis data show that the complexes have composition of ML type with an octahedral geometry for all the complexes. The activation thermodynamic parameters were calculated. The prepared azo dye and its metal complexes were tested against various Gram‐positive and Gram‐negative bacteria and a fungus. Most complexes exhibit antibacterial and antifungal activities against these organisms. Anticancer evaluation studies against standard breast cancer cell line were performed using various concentrations. The activity index was calculated. Copyright © 2016 John Wiley & Sons, Ltd.     

Physicochemical and Biological Characterization of Transition Metal Complexes with a Nitrogen Donor Tetra-dentate Novel Macrocyclic Ligand

A novel tetradentate nitrogen donor [N₄] macrocyclic ligand, i.e. 3,5,13,15,21,22-hexaaza-2,6,12,16-tetramethyl-4,14-dithia-tricyclo[15.3.1.1(7–11)]docosane-1(21),2,5,7,9,11(22),12,15,17,19-decaene, has been synthesized. Mn(II), Co(II), Ni(II) and Cu(II) complexes with this ligand have been prepared and subjected to elemental analyses, molar conductance measurements, magnetic susceptibility measurements, mass, ¹H-n.m.r. (Ligand), i.r., electronic, and e.p.r. spectral studies. On the basis of molar conductance the complexes may be formulated as [M(L)X₂] and [Ni(L)]X₂ [where M = Mn(II), Co(II) and Cu(II), and X = Cl⁻ and NO₃⁻] due to their nonelectrolytic nature in dimethylsulphoxide (DMSO). All the complexes are of the high spin type and are six coordinated. On the basis of i.r., electronic and e.p.r. spectral studies an octahedral geometry has been assigned to Mn(II) and Co(II), square planar for Ni(II) complexes, and tetragonal for Cu(II) complexes. The antimicrobial activities of the ligand and its complexes, as growth inhibiting agents, have been screened in vitro against several species of bacteria and plant pathogenic fungi.     

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 crystal structure of two zinc(II) halide complexes with the symmetrical bidentate Schiff-base ligand (3,4-MeO-ba)2en

Abstract  

In this study two zinc(II) halide complexes with the Schiff-base ligand (3,4-MeO-ba)₂en [N,N′-bis(3,4-dimethoxybenzylidene)ethane-1,2-diamine] have been synthesized and characterized by elemental analyses (CHN), single-crystal X-ray diffraction, Fourier-transform infrared (FT-IR), and ¹H nuclear magnetic resonance (NMR) spectroscopy. The metal-to-ligand ratio was found to be 1:1 within the formula ZnX₂((3,4-MeO-ba)₂en) (X = Br, I). Crystal structure analysis reveals that the coordination geometry around the zinc(II) ions in the two isotypic complexes is distorted tetrahedral. The Schiff-base ligand (3,4-MeO-ba)₂en acts as a chelating ligand and coordinates via two N atoms to the metal center and adopts an (E,E) conformation. The coordination spheres of the metal atoms are completed by the two halide atoms, which are also involved in weak non-classical hydrogen-bonding interactions of the type C–H···X–Zn.     

Template synthesis, spectroscopic studies and biological screening of macrocyclic complexes derived from thiocarbohydrazide and benzil

A novel series of complexes of the type [M(TML)X₂]; where TML is a tetradentate macrocyclic ligand; M = Co(II), Ni(II), Cu(II) or Zn(II); X = Cl⁻, CH₃COO⁻ or NO ₃ ⁻ have been synthesized by template condensation of benzil and thiocarbohydrazide in the presence of divalent metal salts in methanolic medium. The complexes have been characterized with the help of elemental analyses, conductance measurements, molecular weight determination, magnetic measurements, electronic, NMR, infrared and far infrared spectral studies. Electronic spectra along with magnetic moments suggest the six coordinate octahedral geometry for these complexes. The low value of molar conductance indicates them to be non-electrolytes. The biological activities of metal complexes have been tested in vitro against a number of pathogenic bacteria to assess their inhibiting potential.