Complexes of N(4)-cyclohexylsemicarbazones and N(4)-cyclohexylthiosemicarbazones derived from 2-formyl-, 2-acetyl- and 2-benzoylpyridine

2-Formyl-, 2-acetyl- and 2-benzoylpyridine N(4)-cyclohexylsemicarbazone and N(4)-cyclohexylthiosemicarbazone complexes of cobalt(II, III), nickel(II) and copper(II) have been prepared and characterized by molar conductivities, magnetic susceptibilities and spectroscopic techniques. For many of the complexes, coordination is by the neutral ligand, the main exceptions being the cobalt(III) complexes of the three thiosemicarbazones and three of the benzoylpyridine derivatives. Thus, bonding is via the pyridyl nitrogen, azomethine nitrogen and thione/thiolato sulfur. The five-coordinate copper(II) complex of 2-acetylpyridine N(4)-cyclohexylthiosemicarbazone, [Cu(HAc4CHex)Cl₂], approaches square pyramidal stereochemistry with the basal Cu—Cl bond significantly shorter than the apical Cu—Cl bond. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis and spectral studies of macrocyclic Cu(II) complexes by reaction of various diamines,copper(II) perchlorate and 1,4-bis(2-carboxyaldehyde phenoxy)butane

Six macrocyclic complexes, were synthesized by reaction of 1,4-bis(2-carboxyaldehyde phenoxy)butane and various amines and their copper(II) perchlorate complexes were synthesized by template effect reaction of 1,4-bis(2-carboxyaldehyde phenoxy)butane, Cu(ClO₄)₂?·?6H₂O and amines. The metal-to-ligand ratios were found to be 1?:?1. Cu(II) metal complexes are 1?:?2 electrolytes as shown by their molar conductivities (Λ_M) in DMF (dimethyl formamide) at 10^?3?M. The Cu(II) complexes are proposed to be square planar based on elemental analysis, FT–IR, UV–Vis, magnetic susceptibility measurements, molar conductivity measurements, and mass spectra.     

Synthesis,characterization and ascorbic acid oxidase mimetic catalytic activity of copper(II) picolyl hydrazone complexes

Four new picolyl hydrazones were prepared via Schiff-base condensation of picolonic acid hydrazide with α-formyl-(L¹), α-acetyl-(L²), α-benzoyl-(L³) pyridine and α-formyl-(L⁴) thiophene. Copper(II) complexes of these hydrazones and a series of copper(II) complexes containing (L²) and various anions (Cl, Br, NO₃, SCN, SO₄, ClO₄, AcO, PF₆ and BF₄) have been synthesized. Elemental, thermal analysis, molar conductivity, magnetic moment measurements and spectral (i.r., electronic and e.s.r.) studies have been used to characterize the prepared compounds. The overall structure and reactivity of the reported copper(II) chelates critically depend on the ligand structure and the nature of counter anion incorporated in the complex molecule. Octahedral [complex (7)], square-pyramidal [complex (8)] and square-planar monomeric species [complexes (1–6), (9) and (10)] and a dimeric structure with oxygen bridge in square-planar geometry [complexes (11) and (12)] were suggested. The reported copper(II) complexes exhibit promising oxidase catalytic activity towards the aerobic oxidation of vitamin C. A linear correlation exists between the oxidase catalytic activity and the Lewis-acidity of the central copper(II) ion created by the donating properties of the parent ligand, as well the irregularity of the coordination environment. The probable mechanistic implications of the catalytic oxidation reactions are discussed.     

Mixed-ligand metal complexes containing an ONS Schiff base and imidazole/benzimidazole ligands: synthesis,characterization, crystallography and biological activity

Salicylaldehyde-4-methylthiosemicarbazone (H₂MTSali) has been prepared via the condensation reaction of 4-methyl-3-thiosemicarbazide and salicylaldehyde. Four new mixed-ligand copper(II) and nickel(II) complexes with a general formula [M(MTSali)L] (M = Cu²⁺ or Ni²⁺; L = co-ligand) were synthesized, where L is either imidazole (im) or benzimidazole (bzim). The Schiff base and its mixed-ligand complexes were characterized by IR and UV/Vis spectroscopy, and the complexes by molar conductivity and magnetic susceptibility measurements. The spectroscopic data indicated that the Schiff base behaves as a tridentate ONS donor ligand coordinating via the phenoxide-oxygen, azomethine-nitrogen, and thiolate-sulphur atoms. Magnetic data indicate a square planar environment for the nickel(II) complexes while molar conductance values indicate that the metal complexes are essentially non-electrolytes in DMSO solution. X-ray crystallography shows Cu(MTSali)bzim (1) and Ni(MTSali)bzim (3) to be isostructural, with the metal(II) ions being coordinated by a N₂OS donor set that defines an approximate square planar geometry; in both cases, the benzimidazole is splayed with respect to the coordination plane. The copper(II) complexes were active against MDA-MB-231 and MCF-7 breast cancer cell lines, more so than H₂MTSali, whereas the nickel(II) complexes were inactive.     

Synthesis, structure and DNA binding studies of mononuclear copper(II) complexes with mixed donor macroacyclic ligands, 2,6-bis({N-[2&3-(phenylselenato)alkyl]}benzimidoyl)-4-methylphenol

Two new phenol based macroacyclic Schiff base ligands, 2,6-bis({N-[2-(phenylselenato)ethyl]}benzimidoyl)-4-methylphenol (bpebmpH, 1) and 2,6-bis({N-[3-(phenylselenato)propyl]}benzimidoyl)-4-methylphenol (bppbmpH, 2) of the Se₂N₂O type have been prepared by the condensation of 4-methyl-2,6-dibenzoylphenol (mdbpH) with the appropriate (for specific reactions) phenylselenato(alkyl)amine. These ligands with Cu(II) acetate monohydrate in a 2:1 molar ratio in methanol form complexes of the composition [(C₆H₂(O)(CH₃){(C₆H₅)CN(CH₂)_nSe(C₆H₅)}{(C₆H₅)CO}₂Cu] (3 (n = 2), 4 (n = 3)) with the loss of phenylselenato(alkyl)amine and acetic acid. In both these complexes, one arm of the ligand molecule undergoes hydrolysis, and links with Cu(II) in a bidentate (NO) fashion, as confirmed by single crystal X-ray crystallography of complex 3. The selenium atoms do not form part of the copper(II) distorted square planar coordination sphere which has a trans-CuN₂O₂ core. The average Cu–N and Cu–O distances are, respectively, 1.973(3) and 1.898(2) Å. The N–Cu–N and O–Cu–O angles are, respectively, 167.4(11)° and 164.5(12)°. The compounds 1–4 have been characterized by elemental analysis, conductivity measurements, mass spectrometry, IR, electronic, ¹H and ⁷⁷Se{¹H} NMR spectroscopy and cyclic voltammetry. The interaction of complex 3 with calf thymus DNA has been investigated by a spectrophotometric method and cyclic voltammetry.     

Synthesis, spectral characterization and in vitro microbiological evaluation of novel glyoxal, biacetyl and benzil bis-hydrazone macrocyclic Schiff bases and their Co(II), Ni(II) and Cu(II) complexes

A series of binuclear Co(II), Ni(II) and Cu(II) complexes were synthesized by the template condensation of glyoxal, biacetyl or benzil bis-hydrazide, 2,6-diformyl-4-methylphenol and Co(II), Ni(II) or Cu(II) chloride in a 2:2:2 M ratio in ethanol. These 22-membered macrocyclic complexes were characterized by elemental analyses, magnetic, molar conductance, spectral, thermal and fluorescence studies. Elemental analyses suggest the complexes have a 2:1 stoichiometry of the type [M₂LX₂]·nH₂O and [Ni₂LX₂2H₂O]·nH₂O (where M = Co(II) and Cu(II); L = H₂L¹, H₂L² and H₂L³; X = Cl; n = 2). From the spectroscopic and magnetic studies, it has been concluded that the Co(II) and Cu(II) complexes display a five coordinated square pyramidal geometry and the Ni(II) complexes have a six coordinated octahedral geometry. The Schiff bases and their metal complexes have also been screened for their antibacterial and antifungal activities by the MIC method.     

Design,synthesis, characterization and biological studies of copper(II) complexes with 2‐aminobenzimidazole derivatives as biomimetic agents

Four novel copper(II) complexes of 2‐aminobenzimidazole derivatives (obtained from the Knoevenagel condensation of acetylacetone (obtained from acetylacetone and halogen‐substituted benzaldehydes) and 2‐aminobenzimidazole) were synthesized. They were characterized using elemental analysis, molar conductance measurements, and fast atom bombardment mass, Fourier transform infrared, NMR, UV–visible and electron paramagnetic resonance spectroscopies. On the basis of the spectral studies, a distorted square planar geometry was assigned for all the complexes. The antibacterial screening of the ligands and their complexes revealed that all the complexes had higher activities than the free ligands. Superoxide dismutase and antioxidant activities of the copper complexes were also studied. The shifts in ΔE _p, E _1/2, I _pc and I _pa values were explored for the interaction of the complexes with calf thymus DNA using the electrochemical technique.     

Ligational behavior of a bidentate coumarin derivative towards CoII,NiII, and CuII: synthesis,characterization, electrochemistry,and antimicrobial studies

A series of new Co(II), Ni(II), and Cu(II) complexes of Schiff base derived from coumarin have been prepared and characterized by analytical and spectral methods. The Schiff base is synthesized by the condensation of 2,6-diaminopyridine and 3-acetylcoumarin in 1 : 1 stoichiometric ratio. All complexes have 1 : 1 metal : ligand ratio except the nickel complex, where it was found to be 1 : 2. UV-Vis spectra and magnetic moment studies confirm the existence of tetrahedral and octahedral geometries around cobalt(II) and nickel(II) metal ions, respectively, but copper(II) chloride/nitrate/sulfate complexes have square-planar geometry and copper(II) acetate complex is distorted octahedral. ESR spectra of copper complexes at room temperature and liquid nitrogen temperature were tetragonal. All the complexes were found to be more active against bacteria except Ni(II) complex; only CuLSO₄ and CuL(CH₃COO)₂ have shown the enhanced activity against fungi.     

Synthesis, characterization and catalytic oxidation of tetrahydrofuran with 16-membered pentaazabis(macrocyclic) copper(II) complexes; {[Cu([16]aneN5)]2R}4+ (R = aromatic nitrogen–nitrogen linkers)

New square-planar bis(macrocyclic)dicopper(II) complexes containing phenylene bridges between 16-membered pentaaza macrocyclic subunits have been synthesized via in-situ one pot template condensation reaction (IOPTCR) of aromatic nitrogen-nitrogen linker (R = 1,4-phenylenediamine; benzidine; 4,4′-diaminodiphenylmethane; 4,4′-diaminodiphenylether; 4,4′-diaminodiphenylsulfone), formaldehyde, bis(1,3-diaminopropane)copper(II) perchlorate and 1,3-dibromopropane in a 1:4:2:2 molar ratio results in the formation of new series of binuclear copper(II) complexes; 1-phenyl- (1); 1,1′-phenyl- (2); 1,1′-diphenylmethan- (3); 1,1′-diphenylether- (4); 1,1′-diphenylsulfone- (5) bis(1,3,7,11,15-pentaazacyclohexadecane)copper(II)), {[Cu([16]aneN₅)]₂R}(ClO₄)₄″. The formation of the macrocyclic framework and the mode of bonding of the complexes have been confirmed by data obtained from elemental analyses, UV-visible, FT-IR, ¹H-NMR, electronic spectral studies, conductivity and magnetic susceptibility measurements. These bis(macrocyclic) complexes catalyzed efficiently the selective oxidation of tetrahydrofuran into tetrahydrofuran-2-one and a small amount of tetrahydrofuran-2-ol and 4-hydroxybutyraldehyde using dil. H₂O₂ as the oxidant.     

Synthesis,spectral studies,and antimicrobial activity of binary and ternary Cu(II), Ni(II), and Fe(III) complexes of new hexadentate Schiff bases derived from 4,6-diacetylresorcinol and amino acids

Two new hexadentate N₂O₄ donor Schiff bases, H₄L¹ and H₄L², were synthesized by condensation of 4,6-diacetylresorcinol with glycine and alanine, respectively. The structures of the ligands were elucidated by elemental analyses, IR, ¹H NMR, electronic, and mass spectra. Reactions of the Schiff bases with copper(II), nickel(II), and iron(III) nitrates in 1 : 2 molar ratio gave binuclear metal complexes and, in the presence of 8-hydroxyquinoline (8-HQ) or 1,10-phenanthroline (Phen) as secondary ligands (L′), mixed-ligand complexes in two molar ratios 1 : 2 : 2 and 1 : 2 : 1 (L¹/L² : M : L′). The complexes were characterized by elemental and thermal analyses, IR, electronic, mass, and ESR spectral studies, as well as conductivity and magnetic susceptibility measurements. The spectroscopic data reveal that the Schiff-base ligands were dibasic or tetrabasic hexadentate ligands. The coordination sites with the metal ions are two azomethine nitrogens, two oxygens of phenolic groups, and two oxygens of carboxylic groups. Copper(II) complexes were octahedral and square planar while nickel(II) and iron(III) complexes were octahedral. The Schiff bases, H₄L¹ and H₄L², and some of their metal complexes showed antibacterial activity towards Gram-positive (Staphylococcus aureus and Streptococcus pyogenes) and Gram-negative (Pseudomonas fluorescens and Pseudomonas phaseolicola) bacteria and antifungal activity towards the fungi Fusarium oxysporium and Aspergillus fumigatus.     

Synthesis,characterization, and catalytic oxidation of ethylbenzene over host (zeolite-Y)/guest (copper(II) complexes of tetraaza macrocyclic ligands) nanocomposite materials

Cu(II) complexes of 14- and 16-membered tetraaza macrocyclic ligands have been encapsulated in nanopores of zeolite-Y by a two-step process in the liquid phase: (1) adsorption of [bis(diamine)copper(II)] (diamine = 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene, and 1,3-diaminobenzene); [Cu(N–N)₂]²⁺–NaY; in the nanopores of the zeolite-Y and (2) in situ condensation of the copper(II) precursor complex with ethylcinnamate. The new host–guest nanocomposite materials were characterized by chemical analysis and spectroscopic methods. The “neat” and encapsulated complexes exhibit good catalytic activity in the oxidation of ethylbenzene at 333 K, using tert-butyl hydroperoxide as the oxidant. Acetophenone was the major product though small amounts of o- and p-hydroxyacetophenones were also formed revealing that C–H bond activation takes place both at benzylic and aromatic ring carbon atoms.     

Synthesis,crystal structure,and magnetism of a binuclear Cu(II) complex with double azido as asymmetric basal–apical end-on bridged ligand

A new binuclear copper(II) complex, [Cu₂(μ_1,1-N₃)₂(PP)₂)] ? 2ClO₄ (PP = 2,6-dipyrazol-1-yl-pyridine), was synthesized with double azide as asymmetric end-on bridge ligand and 2,6-dipyrazol-1-yl-pyridine as the terminal ligand. The crystal structure was determined by X-ray crystallography. Cu(II) is located in a distorted square pyramidal geometry, and azide bridges the equatorial-axial linking two Cu(II) atoms with a separation of 3.3595(11) Å. The fitting for the data of the variable-temperature (2–300 K) magnetic susceptibilities by using the Curie–Weiss law gives the Weiss temperature θ = ?7.830 K, indicating a very weak anti-ferromagnetic interaction between the bridging Cu(II) complexes.     

2,6-Diacetyl- and 2,6-diformylpyridine bis(N4-substituted thiosemicarbazones) and their copper(II) and nickel(II) complexes

2,6-Diformylpyridine bis(N4-methylthiosemicarbazone) and bis(N4-dimethylthiosemicarbazone), H₂2,6Fo4M and H₂2,6Fo4DM, respectively, and 2,6-diacetylpyridine bis(N4-methylthiosemicarbazone) and bis(N4-dimethylthiosemicarbazone), H₂2,6Ac4M and H₂2,6Ac4DM, and their copper(II) and nickel(II) complexes have been synthesized. The ¹H-n.m.r. spectra of the free bis(thiosemicarbazones) show that, most often, one of the thiosemicarbazone moieties is hydrogen bonded to the pyridine nitrogen, and in [²H₆]-DMSO there is interaction with solvent oxygen. Golden yellow H₂2,6Ac4DM has a bifurcated hydrogen bonding interaction by one of the thiosemicarbazone moieties resulting in conjugation. Coordination to copper(II) and nickel(II) centers is via the pyridine nitrogen, amine nitrogen and thiolato sulfur and most of the complexes formed are polynuclear with thiosemicarbazone moieties from the same ligand coordinating to different metal centers.     

Synthesis and structure of aqua-2′,?-(2,6-pyridindiyldiethylidene) dioxamohydrazide-copper(II) hydrate

In a template synthesis from copper(II) acetate, 2,6-diacetylpyridine, and semioxamazide (NH₂CO CONHNH₂), two copper(II) complexes, [Cu(dapsox)(H₂O)]·H₂O and [Cu(Hdapsox)](H₂O)]ClO₄, (where H₂dapsox = 2′,2?-(2,6-pyridindiyldiethylidene)dioxamohydrazide) were obtained and characterized. The structure of the former complex was determined by a single-crystal X-ray analysis. Cu^II is located in a square pyramidal environment. The polydentate ligand, dapsox²⁻ is coordinated in dianionic form, as an unsymmetrical quadridentate planar system forming one-membered and two-five-membered metal-chelate rings. The fifth coordination site is occupied by a water molecule.     

Antioxidant,DNA interaction,molecular docking and cytotoxicity studies of aminoethylpiperazine‐containing macrocyclic binuclear copper(II) complexes

A series of new macrocyclic binuclear copper(II) complexes of the type [Cu₂L^1–5(ClO₄)](ClO₄) ( 1 – 5 ) were synthesized by template condensation between precursor compounds 2,6‐bis(4‐aminoethylpiperazin‐1‐ylmethyl)‐4‐substituted phenols and 2,6‐diformyl‐4‐substituted phenols. The synthesized precursors and complexes were characterized using regular physicochemical techniques. The rate constant values obtained for the hydrolysis of 4‐nitrophenylphosphate were in the range 1.83 × 10⁻²–4.19 × 10⁻² min⁻¹. Antioxidant studies against 2,2′‐diphenyl‐1‐picrylhydrazyl revealed the antioxidant potency of the synthesized complexes. Binding studies of the complexes with calf thymus DNA were conducted using electronic, viscometric and voltammetric techniques, and the obtained results suggested a non‐covalent groove mode of binding. The oxidative cleavage of pBR322 DNA in the presence of co‐reactant H₂O₂ and radical scavengers showed single strand scission and involvement of H₂O₂ radical in the cleavage process. Molecular docking studies were performed to insert complexes into the crystal structures of 1BNA and VEGFR kinase at active sites to determine the possible binding mode and predominant binding interactions. In vitro cytotoxicity of the complexes was tested against human epidermoid carcinoma cells (A431) by MTT assay, which revealed the effective anticancer activity of the complexes. Live cell and fluorescent imaging of A431 cells showed that the complexes induce cell death through apoptosis.     

<Emphasis Type="Italic">Ab Initio</Emphasis> quantum chemical calculation of the structures of coordination compounds arising at template synthesis in ion M(II)-hydrozinomethane thiohydrazide-acetone (M = Co,Ni, Cu) systems

Using a hybrid B3LYP density functional method with the 6-31G(d) basis set and the Gaussian-98 program, the geometrical parameters of macrocyclic complexes of Co(II), Ni(II) and Cu(II) with NNSS-coordination of donor centers of the chelate ligand, formed due to template processes in M(II)-hydrozinomethane thiohydrazide-acetone systems, are calculated. Coordinates of atoms, selected bond lengths and angles, and dihedral angles in complexes with MN₂S₂ metal-chelate site are given. It is noted that for all considered M(II) ions the additional six-membered metal cycle, formed because of template stitching, is turned at a considerable angle to two five-membered cycles, and this cycle itself is not planar either.     

New copper(II) and zinc(II) complexes based on azo Schiff base ligand: Synthesis,crystal structure,photoisomerization study and antibacterial activity

Newly synthesized mononuclear copper(II) and zinc(II) complexes containing an azo Schiff base ligand (L), prepared by condensation of 2-hydroxy-5-(o-tolyldiazenyl)benzaldehyde and propylamine, were obtained and then characterized using infrared and NMR spectroscopies, mass spectrometry and X-ray diffraction. Ligand L behaves as a bidentate chelate by coordinating through deprotonated phenolic oxygen and azomethine nitrogen. The copper and zinc complexes crystallize in triclinic and orthorhombic systems, respectively, with space groups P⁻1 and Pca2₁. In these complexes, the Cu(II) ion is in a square planar geometry while the Zn(II) ion is in a distorted tetrahedral environment. The photochemical behaviors of ligand L, [Cu(L)₂] and [Zn(L)₂] were investigated. The azo group in L underwent reversible trans–cis isomerization under UV and visible irradiation. This process was inhibited for the complexes. In addition, ligand L and its copper and zinc complexes were assessed for their in vitro antibacterial activities against four pathogenic strains.     

New acyclic Schiff-base copper(II) complexes and their electrochemical,catalytic, and antimicrobial studies

A new series of acyclic mononuclear copper(II) complexes have been prepared by Schiff-base condensation derived from 5-methylsalicylaldehyde, diethylenetriamine, tris(2-aminoethyl) amine, triethylenetetramine, N,N-bis(3-aminopropyl)ethylene diamine, N,N-bis(aminopropyl) piperazine, and copper perchlorate. All the complexes were characterized by elemental and spectral analyses. Electronic spectra of the complexes show a d–d transition in the range 500–800?nm, electrochemical studies of the complexes show irreversible one-electron-reduction process around ?1.10 to ?1.60?V. The reduction potential of the mononuclear copper(II) complexes shifts toward anodic direction upon increasing the chain length of the imine compartment. ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry, with nuclear hyperfine spin 3/2. The copper(II) complexes show a normal room temperature magnetic moment value μ _eff?=?1.72–1.76?BM, close to the spin-only value of 1.73?BM. Electrochemical and catalytic studies of the complexes were compared on the basis of increasing the chain length of the imine compartment. All the complexes were screened for antifungal and antibacterial activities.     

Synthesis and spectral characterization of zinc(II), copper(II), nickel(II) and manganese(II) complexes derived from <Emphasis Type="Italic">bis</Emphasis>(2-hydroxy-1-naphthaldehyde) malonoyldihydrazone

The present study shows that the reaction of different salts of the same metal with sterically crowded dihydrazone bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone (CH₂LH₄) in ethanol/aqueous media gives complexes of different stereochemistry. While the reaction of zinc(II) and copper(II) sulphate with dihydrazone yields tetrahedral complexes, the zinc(II) and copper(II) chlorides give square pyramidal and distorted octahedral complexes, respectively. On the other hand, nickel(II) sulphate and chloride, both give high-spin octahedral complexes with dihydrazone, manganese sulphate gives low-spin octahedral and manganese(II) chloride gives high-spin octahedral complexes. The reaction of these complexes with KF has been investigated. All of the products have been characterized by analytical, magnetic moment and molar conductivity data. The structures of the complexes have been established by spectroscopic studies.     

General routes to porous metal oxides via inorganic and organic templates

The generation of porous metal oxides by removal of template molecules from inorganic polymers formed by sol-gel type hydrolysis and condensation of metal alkoxides is described. The template molecules include organic polymers, copper (II) ions in hybrid copper oxide/silica sols and copper (II) bis(hexafluorocetylacetonate) (hfac). Neutron scattering experiments on the system in which polyacrylic acid (Mw=2,000 Daltons) is used as an organic template to generate microporous tin oxide show that removal of the template generates skeletal voids. In a second series of experiments, mixed copper/silicon oxide xerogels were prepared by hydrolysis of mixtures of Si(OEt)₄ and Cu(OCH₂CH(CH₃)N(CH₃)H)₂ in the ratios of Si:Cu=2:1, 4:1, 9:1. Selective removal (etching) of the copper component generates porous silica. Neutron scattering data and BET surface area measurements are consistent with the creation of pores with molecular dimensions (micropores, 10 Å or less). In the third strategy, Si(OEt)₄ is hydrolyzed in the presence of Cu(hfac)₂, a volatile, inert inorganic template, in a 4 to 1 molar ratio. Removal of the template from the xerogel at 100°C in vacuo affords microporous silica.