Thermochemical studies on copper(II) and nickel(II) complexes of the Schiff base derived from 2-(2-aminophenyl)benzimidazole and salicylaldehyde

Microcalorimetric measurements were made on copper(II) and nickel(II) complexes of the Schiff base (L) derived from 2-(2-aminophenyl)benzimidazole and salicylaldehyde. The complexes were of the general type MX₂L₂ with M = Cu or Ni, and X = Cl, Br, NO₃ or ClO₄. The enthalpies of decomposition of the solid complexes to solid products, MX₂ and L, were derived. Despite showing some variation depending on the anion, the average binding enthalpy of the ligand to nickel was 47.5 ± 7.3 kJ mol⁻¹, greater than that to copper, 16.8 ± 3.5 kJ mol⁻¹ by 30.7 ± 8.1 kJ mol⁻¹.     

DNA-binding,antioxidant activity and solid-state fluorescence studies of copper(II), zinc(II) and nickel(II) complexes with a Schiff base derived from 2-oxo-quinoline-3-carbaldehyde

A Schiff base derived from 2-oxo-quinoline-3-carbaldehyde-4-aminophenazone and its Cu(II), Zn(II) and Ni(II) complexes were synthesized. The molecular structures of the Zn(II) and Ni(II) complexes were determined by X-ray crystal diffraction. The DNA-binding modes of the compounds were investigated by spectroscopic methods, viscosity measurements and ethidium bromide-DNA displacement experiments. The experimental evidence indicated the compounds interact with calf thymus DNA through intercalation. Additionally, the compounds exhibited potential antioxidant properties in in vitro studies, and the Cu(II) complex was the most effective. The solid-state fluorescence properties of the Zn(II) complex were studied.     

Cobalt(II), nickel(II) and copper(II) complexes of a Schiff base ligand: synthesis,structural characterization and luminescence properties

A Schiff base ligand (HL), 2,4-dimethoxy-N-(5-chloro-2-hydroxybenzylidene)-benzenamine, derived from 5-chloro-2-hydroxybenzaldehyde and 2,4-dimethoxyaniline, and its metal complexes [Co(L)₂]·CH₃OH (1), [Ni(L)₂] (2), [Cu(L)₂] (3) have been synthesized. The compounds were characterized by analytical and spectroscopic methods. In addition, the structures of the Schiff base HL and its Co(II) complex were determined by single-crystal X-ray analysis. The Co(II) center is six-coordinate, being coordinated to two imine nitrogen, two phenolate oxygen and two methoxy oxygen atoms of two crystallographically independent Schiff base ligands. Luminescence properties of HL and its complexes were investigated both in solution and in the solid state.     

Synthesis, characterization, and X-ray crystal structures of copper(II) and nickel(II) complexes with Schiff base

New copper(II) complexes, [Cu₂L¹L²] · ClO₄ (I) and [Ni(L³)₂] (II), where L¹ is the monoanionic form of 2-[1-(2-emthylaminoethylimino)ethyl]phenol, L² is the dianionic form of N,N′-ethylene-bis(2-hydroxyacetophenonylideneimine), L³ is the mono-anionic form of 2-(1-iminoethyl)phenol, were prepared and characterized using elemental analysis, FT-IR spectroscopy, and X-ray single-crystal diffraction. In complex I, the Cu(1) atom is coordinated by the NNO tridentate ligand L¹ and the two phenolate O atoms of L², forming a square pyramidal geometry. The Cu(2) atom in complex I is coordinated by the NNOO tetradenate ligand L², forming a square planar geometry. The Ni atom in complex II is coordinated by two phenolate O and two imine N atoms from two ligands L³, forming a square planar geometry. In the crystal structure of I, the perchlorate anions are linked to the dinuclear copper(II) complex cations through intermolecular N-H...O hydrogen bonds. In the crystal structure of II, the mononuclear nickel complex molecules are linked through intermolecular N-H...O hydrogen bonds, forming a trimer.     

Synthesis and characterization of copper(II) and nickel(II) complexes of the Schiff base derived from 2-(2-aminophenyl)benzimidazole and salicylaldehyde

Summary Copper(II) and nickel(II) complexes with the Schiff base derived from 2-(2-aminophenyl)benzimidazole and salicylaldehyde, L, have been prepared. They are of the general types ML₂X₂ (M = Ni or Cu and X = Cl, Br, NO₃ or ClO₄) and NiL(NCS)₂.The compounds have been characterized by elemental analyses, magnetic measurements, e.s.r., electronic and i.r. spectra studies. The i.r. spectra suggest that the molecule, and not the anion, of the Schiff base is coordinated as a bidentate ligand with the metal ion. Possible structures for the complexes have been proposed.     

Equilibrium studies on Schiff base complexes of copper(II) and nickel(II): Ligand substitution and formation of mixed ligand complexes

Summary Vis spectrophotometry has been used to study various ligand substitution equilibria (1) and (2) involving four-coordinate copper(II) and nickel(II) his chelate complexes in methanol, propan-2-ol and toluene. MA₂ + HB MAB+HA, K₁ (1) MAB + HB MB₂ + HA, K₂ (2) The Schiff base ligands, HA and HB, which are monobasic and bidentate, represent salicylaldimine type N,O-ligands ( HSA=NR) (1) or pyrrole-2-aldimine type N,N-ligands ( HPA=NR) (2) with different branching at the - or (3-carbon of the organic group R. For both types of ligand the relative thermodynamic stability of their copper and nickel complexes is governed mainly by the steric demands of R, which determine the degree of tetrahedral distortion. The order of stability as given by = K₁ K₂ is: t-Bu < neo-Pent < i-Pr < i-Bu < Et < n-Pr. The K₁/K₂ ratio is strongly solvent dependent in the sense that the mixed ligand species MAB is stabilised in toluene relative to methanol. Such a solvent effect is not observed for . The MAB complexes could not be isolated. The vis spectrum of the mixed ligand species Ni(SA=NiPr, SA=NEt) was calculated by computer fitting of the experimental data.     

Nicke(II) complexes of half unit,symmetric and unsymmetric Schiff base ligands

Summary The template reaction of isonitrosoacetylacetone (Hina) witho-phenylenediamine (o-phenen) in the presence of (MeCO₂)₂Ni·4H₂O in EtOH yielded three types of nickel(II) complexes (depending on the molar ratio of the reactants) formulated as L¹Ni(O₂CMe)·2H₂O (1), (L¹)₂Ni (2), and L²Ni·H₂O (3). HL¹ and H₂L² are the half unit and symmetric Schiff base ligands obtained from the (11) and (21) condensation of (Hina) with (o-phenen) respectively. The (11) molar ratio reaction of (1) with either acetylacetone (Hacac) or (Hina) in CHCl₃ led to the formation of mixed ligand complexes L¹Ni(acac)·H₂O (4) and L¹Ni(ina)·H₂O (5) whereas a similar reaction with salicylaldehyde (Hsal) produced L³Ni (6); H₂L³ is the unsymmetric Schiff base formed by the (11) condensation of the amino group in (1) with (Hsal). Analytical, spectral and magnetic moment evidence are compatible with the suggested structures of the metal complexes.This paper is a summary of the M.Sc. thesis of S. M. Imam.     

Three heterotrinuclear Schiff base complexes of nickel(II) with cobalt(II), copper(II) and manganese(II)

The title compounds, bis­(di­methyl­form­amide)‐1κO,3κO‐bis{μ‐2,2′‐[2,2′‐di­methyl­propane‐1,3‐diyl­bis­(nitrilo­methylidyne)]­diphenolato}‐1κ⁴N,N′,O,O′:2κ²O,O′;2κ²O,O′:3κ⁴N,N′,O,O′‐di‐μ‐nitrito‐1:2κ²N:O;2:3κ²O:N‐dinickel(II)­cobalt(II), [CoNi₂(NO₂)₂(C₁₉H₂₂N₂O₂)₂(C₃H₇NO)₂], (I), ‐copper(II), [CuNi₂(NO₂)₂(C₁₉H₂₂N₂O₂)₂(C₃H₇NO)₂], (II), and ‐manganese(II), [MnNi₂(NO₂)₂(C₁₉H₂₂N₂O₂)₂(C₃H₇NO)₂], (III), consist of centrosymmetric linear heterotrinuclear metal complexes. The three complexes are isostructural. There are three bridges across the Ni–M atom pairs (M is Co²⁺, Cu²⁺ or Mn²⁺) in each complex, involving two O atoms of a μ‐N,N′‐bis­(salicyl­idene)‐2,2′di­methyl‐1,3‐propane­diaminate ligand and an N—O moiety of a μ‐nitrito group. The coordination sphere around each metal atom, whether Co²⁺, Cu²⁺, Mn²⁺ or Ni²⁺, can be described as distorted octahedral. The Ni?M distances are 2.9988 (5) Å in (I), 2.9872 (5) Å in (II) and 3.0624 (8) Å in (III).     

Spectral and magnetic studies of polynuclear copper(II) complexes of Schiff base derived from ethylenediamine and ethylacetoacetate

Summary The Schiff base (L), prepared by the condensation of two molecules of ethyl acetoacetate and one molecule of ethylenediamine reacts with copper(II) chloride to give poiynuclear complexes of the type Cu₃L Cl₆, Cu₄L Cl₈, Cu₅L Cl₁₀, Cu₆L Cl₁₂, Cu₇L Cl₁₄ and Cu₈L Cl₁₆. Elemental analyses, molar conductivities, magnetic susceptibilities, x-ray powder diffraction and i.r. spectral studies have been used to characterize the complexes. The i.r. spectra show that the Schiff base binds in a tetradentate manner and the spectral and magnetic studies suggest the presence of a chlorine bridge between the copper atoms. The magnetic susceptibility of the complexes follows the Curie-Weiss law.     

Homogeneous and heterogeneous styrene epoxidation catalyzed by copper(II) and nickel(II) Schiff base complexes

Both monomeric Schiff base complexes and 1D helical polymeric complexes of Cu(II) and Ni(II) were synthesized and characterized by physicochemical and spectroscopic methods. X-ray single-crystal studies were made on [K₂(CuL)₂Ni(CN)₄]_n·0.5nEt₂O and [K₂(NiL)₂Ni(CN)₄]_n·0.5nEt₂O. The polymers were screened as heterogeneous catalysts for styrene epoxidation. For comparison, the catalytic properties of the homogeneous and heterogeneous catalysts were also examined under identical reaction conditions, and the influence of various solvents and oxidants was studied. The polymeric catalysts showed better activities in chloroform when using tert-butyl hydroperoxide as oxidant, suggesting that heterogenization increased the activity of the catalyst under this condition.     

Synthesis,crystal structures and yeast RNA-binding properties of copper(II) and nickel(II) complexes with a bidentate Schiff base

Abstract  

Trans-CuL₂ and cis-NiL₂ (L = 1-((furan-2-yl)methylene)-4-phenylthiosemicarbazide) were synthesized and characterized by physico-chemical and spectroscopic methods. Their X-ray crystal structures were determined. The complexes contain the same bidentate Schiff base ligand, but with different cis-NiN₂S₂ and trans-CuN₂S₂ square-planar coordination geometries. Three-dimensional supramolecular networks were formed through “face to face” π–π conjugated systems between phenyl and furan rings. The interactions with yeast RNA (yRNA) were investigated by UV spectra and electrochemical methods, which showed that the complexes intercalated into yRNA. The bonding of trans-CuL₂ to yRNA is the stronger of the two, suggesting that the trans geometry is more favorable for interaction with RNA.     

Cyclovoltammetric and spectroscopic characterization of optically active cobalt(II) and copper(II) complexes with the Schiff base derived from (N,N′)-(1R,2R)-(−)-cyclohexylenediamine and 2-hydroxyacetophenone

The Schiff base prepared by reacting (–)-(1R,2R)-1,2-cyclohexanediamine with 2-hydroxyacetophenone was used as a ligand for Co^II and Cu^II. The coordination compounds were studied by u.v.–vis. absorption and by circular dichroism (c.d.) spectroscopy in solution. The complexes are four-coordinated in a slightly distorted square planar symmetry. The distortion from planarity is a main factor influencing the chiral surroundings of the metal ion. The d–d and c.t. transitions are consistent with the observed distortion, which arises from intramolecular interactions between the methyl groups attached to the Schiff base imine carbon and hydrogen atoms of the cyclohexane ring. The electrochemical properties of the Co^II and Cu^II complexes were observed in MeCN but investigations revealed weaker oxygen activation than of Co^II analogue with salicylaldehyde. The Cu^II complex is reduced in H₂O to Cu^I which disproportionates to Cu^II and Cu⁰.     

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.     

Synthesis,crystal structure and antibacterial activity of four mononuclear Schiff base complexes of copper(II) and nickel(II)

Transition Metal Chemistry - Three mononuclear copper(II) complexes, viz. [CuL1] (1), [CuL2] (2), [CuL3] (3), and one nickel(II) complex, viz.[NiL3] (4) where...     

Synthesis,characterization and electrochemical properties of copper(II) complexes derived from succinoyldihydrazine Schiff base ligands

Four new copper(II) complexes of the composition [Cu(H₂L)(H₂O)] have been synthesized by template method from reaction of copper(II) acetate, succinoyldihydrazine and some o-hydroxy aromatic aldehydes and ketones in aqueous methanol media. The composition of the complexes has been established on the basis of data obtained from analytical and mass spectral studies. The structure of the complexes has been discussed in the light of molar conductance, magnetic moment, Uv-vis, EPR and IR spectral studies. All of the complexes are non-electrolyte in DMSO. The μ_eff values for the complexes fall in the region 1.76–1.85 BM which rules out the possibility of any M–M interaction in the structural unit of the complexes. The ligands coordinate to the metal centre in enol form through phenolate/naphtholate oxygen atoms and azomethine nitrogen atoms. The NMR spectra show that ligands are present in anti-cis configuration in uncoordinated state. In all of the complexes the copper centre adopts square pyramidal stereochemistry. The unpaired electron is present in $d_{x^2-y^2}$ orbital in the ground state for copper centre in the complexes. The electron transfer reactions for the complexes have been studied by cyclic voltammetry.     

New complexes of iron(III), cobalt(II), nickel(II) and copper(II) with Schiff bases derived from 2-aminocyclopent-1-ene-1-dithiocarboxylic acid

Summary Fe^III, Co^II, Ni^II and Cu^II, complexes of a new Schiff base ligand, prepared by condensing 2-aminocyclopent-1-ene-1-dithiocarboxylic acid with benzaldehyde (ACB), and also Cu^II and Ni^II complexes of a second Schiff base ligand prepared by condensing 2-aminocyclopent-1-ene-1-dithiocarboxylic acid with salicylaldehyde (ACS), have been prepared and characterized by elemental analyses, conductivity measurements, magnetic and spectral (electronic, i.r. and e.p.r.) studies. The i.r. spectra suggest that both ACB and ACS are acting as bidentate ligands, coordinating through one of the sulphur atoms and through the azomethine nitrogen atom. The magnetic moment of the Fe^III complex indicates spin crossover behaviour. Square planar structures have been assigned to the Cu^II and Ni^II complexes and a tetrahedral structure to the Co^II complex. The e.p.r. spectra of the Cu^II complexes suggest a square planar environment with rhombic distortion around the Cu^II ion.