Spectral,magnetic, thermal and electrochemical studies on new copper(II) thiosemicarbazone complexes

The chelation behavior of some =N(1) and NH(4) thiosemicarbazones towards copper(II) ions has been investigated. The isolated complexes are characterized by elemental analysis, magnetic moment, electronic, IR, ESR and ms spectra, and by thermal and voltammetric measurements. The substituents on =N(1) and/or NH(4) thiosemicarbazones and the log K values of the ligands play an important role in complex formation. The IR spectra showed that the reagents HAT, HAET, HAPT, HApClPT, H₂ST and HBT are deprotonated in the complexes and act as mononegative SN donors; H₂SET, H₂SpClPT, H₂HyMBPT and H₂HyMBpClPT, as binegative NSO donors while H₂SPT is a mononegative NSO donor. The ESR spectra of the complexes are quite similar and exhibit axially symmetric g-tensor parameters with g _‖?>?g _⊥?>?2.0023. The loss of thiol and/or hydroxyl hydrogen was confirmed from potentiometric titrations of the ligands and their copper(II) complexes. The protonation constants of the ligands as well as the stability constants of their Cu(II) complexes were calculated. Thermogravimetric analysis of the complexes suggests different decomposition steps. The Coats–Redfern and Horowitz–Metzger equations have been used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition steps of some complexes. The redox properties, nature of the electroactive species and the stability of the complexes towards oxidation are strongly dependent on the substituents on the precursor NH(4) thiosemicarbazone. The redox data are discussed in terms of the kinetic parameters and the reaction mechanism.     

Chromotropism studies on copper(II) compounds. Part II. Dinuclear copper(II) complexes with triply-bridged hydroxo,acetate, and halo ligands

Abstract

Two triply-bridged dinuclear copper(II) complexes of formula [LCu(μ-OH)(μ-OAc)(μ-X)CuL]X?0.5H₂O where L is a bidentate ligand of N-(pyridine-2-ylmethyl)propane-2-amine and X=Cl, 1 and Br, 2 were synthesized and characterized by elemental analyses, spectroscopic techniques (IR, UV–Vis, EPR), thermal analysis, conductance measurements, and single-crystal X-ray structure determination. The structures of both complexes are similar. The complexes show a distorted square-pyramidal arrangement around each copper(II) ion with a CuN₂O₂X chromophore in which both copper(II) ions are connected by a hydroxo bridge and a triatomic syn-syn carboxylato bridge in equatorial positions and a halide ion bridge at the axial site. The chromotropism behavior of the complexes, including solvato-, thermo-, and halochromism, were investigated in detail. Their halochromism was investigated in the pH range of 2.0–11.0 by visible absorption spectroscopy. The reversible color variations from blue to colorless are attributable to deprotonation and protonation of the ligands. The complexes show reversible thermochromism in solution due to dissociation and recombination of ligands to copper ions.     

Interactions of nitrogen-donor bio-molecules with dinuclear platinum(II) complexes

Substitution reactions of the dinuclear Pt(II) complexes, [{Pt(en)Cl}₂(μ-pz)]²⁺ (1), [{Pt(dach)Cl}₂(μ-pz)]²⁺ (2) and [{Pt(dach)Cl}₂(μ-4,4?-bipy)]²⁺ (3), and corresponding aqua analogs with selected biologically important ligands, viz. 1,2,4-triazole, L-histidine (L-His) and guanosine-5?-monophosphate (5?-GMP) were studied under pseudo-first-order conditions as a function of concentration and temperature using UV–vis spectrophotometry. The reactions of the chloride complexes were followed in aqueous 25 mmol L^?1 Hepes buffer in the presence of 40 mmol L^?1 NaCl at pH 7.2, whereas the reactions of the aqua complexes were studied at pH 2.5. Two consecutive reaction steps, which both depend on the nucleophile concentration, were observed in all cases. The second-order rate constants for both reaction steps indicate a decrease in the order 1 > 2 > 3 for all complexes. Also, the pK_a values of all three aqua complexes were determined. The order of the reactivity of the studied ligands is 1,2,4-triazole > L-His > 5?-GMP. ¹H NMR spectroscopy and HPLC were used to follow the substitution of chloride in the dichloride 1, 2, and 3 complexes by guanosine-5?-monophosphate (5?-GMP). This study shows that the inert and bridging ligands have an important influence on the reactivity of the studied complexes.     

Synthesis and spectroscopic studies of copper(II) and nickel(II) complexes containing hydrazonic ligands and heterocyclic coligand

Two types of copper(II) and nickel(II) complexes derived from benzophenone anthranoylhydrazone (L1), 2-acetonaftanone anthranoylhydrazone (L2), 4-phenylacetonaftonone anthranoylhydrazone (L3), benzophenone salicyoylhydrazone (L4), 2-acetonaftanon salicyoylhydrazone (L5), 4-phenylacetonaftanon salicyoylhydrazone (L6) and bidentate heterocyclic base [1,10-phenanthroline (phen)] with general stoichiometry [ML2] and [ML(phen)]Cl have been synthesized and characterized by elemental analysis, infrared spectra, UV-vis electronic absorption spectra and magnetic susceptibility measurements. The effect of varying pH and solvent on the absorption behavior of both ligands and complexes have been investigated. According to the IR spectra, the ligands act as monobasic bidentate and coordination takes place in the enol tautomeric form.     

Molecular complexes of hydrazides with copper(II)

Summary The reaction of substituted hydrazides with copper(II) chloride was investigated in the solid state or in solution in order to account for substituent effects. Spectroscopic results and values of the formation constants indicate the occurrence of strong complexes.

---

Molekulare Komplexe von Hydraziden mit Kupfer(II)

Zusammenfassung Die Reaktionen von substituierten Hydraziden mit Kupfer(II)chlorid wurden im Festzustand und in Lösung untersucht. Die spektroskopischen Ergebnisse und die Werte der Bildungskonstanten zeigen die Koordinierung zu starken Komplexen an.

     

Polynuclear copper (II) complexes with aminoalcohol ligands

Copper complexes with aminoalcoholato ligands have attracted much attention recently because of their potential applications in ceramic materials. This review deals with polynuclear copper (II) complexes containing bidentate and triden-tate aminoalcoholato ligands. The focus of this article is on the synthesis, structure, and magnetic properties of polynuclear copper (II) complexes obtained recently by our group. Some relevant work reported previously by other researchers is also included.Dedicated to Professor Jiaxi Lu on the occasion of his 80th birthday.     

Thermal behaviour of hydrated copper(II) complexes

Dehydration steps of aquacopper(II) complexes with homogeneous and heterogeneous coordination sphere are investigated from the view point of structural changes taking place under their heating to the decomposition temperature and during the dehydration. The role of loosening of intra-and intermolecular hydrogen bonds in the decomposition reaction for the structure changes of the remainder, the structural presumptions of the reactants for lower hydrates formation are discussed. Activation parameters of dehydration were found to be the lower, the smaller are the structure differences between the reactants and products. They do not reflect the bond length central atomvolatile ligand, much more the overall structure differences between the starting and resulting compounds. From all data on crystal and molecular structures of dehydrated compounds is the reaction pathway best indicated by anisotropic temperature parameters of donor atoms corrected for the thermal movement of the central atom: the higher these values in the bond direction are, the lower the values of activation energies of dehydration are.     

Synthesis,structure, EPR,and DFT calculation on dinuclear paddle wheel Cu(II) complexes with bis-chelate rings

A series of diester-dicarboxylic acids, L¹H₂, L²H₂, L³H₂, L⁴H₂, and L⁵H₂ and their dinuclear Cu₂ complexes [Cu(L¹)CH₃CN]₂ (1), [Cu(L²)H₂O]₂ (2), [Cu(L³)CH₃CN]₂ (3), [Cu(L⁴)EtOH]₂ (4), and [Cu(L⁵)CH₃CN]₂ (5), were synthesized. The crystal structures obtained for 1, 2, and 4 and the density functional theory optimized structures for 2, 3, and 5 illustrated the formation of tetracarboxylate “paddle wheel” complexes. The phthalyl and diphenyl head groups and the spacer moieties were appropriately altered and the size of the chelate ring expanded from 15-membered in 1 to 21-membered in 5. The dinuclear units have strong Cu–Cu interaction with EPR spectra exploring spin coupled features.     

Synthesis of unsymmetrical compartmental oxime nickel(II) and copper(II) complexes: spectral, electrochemical and magnetic studies

A new series of binuclear unsymmetrical compartmental oxime complexes (1–5) [M₂L] [M=Cu(II), Ni(II)] have been synthesized using mononuclear complex [ML] (L=1,4-bis[2-hydroxy-3-(formyl)-5-methylbenzyl]piperazine), hydroxylamine hydrochloride and triethylamine. In this system there are two different compartments, one has piperazinyl nitrogens and phenolic oxygens and the other compartment has two oxime nitrogens and phenolic oxygens as coordinating sites. The complexes were characterized by elemental and spectral analysis. Electrochemical studies of the complexes show two step single electron quasi-reversible redox processes at cathodic potential region. For copper complexes E¹ _pc=−0.18 to −0.62 and E² _pc=−1.18 to −1.25 V, for nickel complexes E¹ _pc=−0.40 to −0.63 and E² _pc=−1.08 to −1.10 V and reduction potentials are sensitive towards the chemical environment around the copper and nickel atoms. The nickel(II) complexes undergo two electrons oxidation. The first one electron oxidation is observed around +0.75 V and the second around +1.13 V. ESR Spectra of the binuclear copper(II) complexes [Cu₂L](ClO₄), [Cu₂L(Cl)], [Cu₂L(NO₃)] shows a broad signal at g=2.1 indicating the presence of coupling between the two copper centers. Copper(II) complexes show a magnetic moment value of μ_eff around 1.59 B.M at 298 K and variable temperature magnetic measurements show a −2J value of 172 cm⁻¹ indicating presence of antiferromagnetic exchange interaction between copper(II) centres.     

Catechol oxidase activity of dinuclear copper(II) complexes of Robson type macrocyclic ligands: Syntheses, X-ray crystal structure, spectroscopic characterization of the adducts and kinetic studies

Five dinuclear copper(II) complexes, [Cu₂L¹(N₃)₂·2H₂O] (1), [Cu₂L²(N₃)₂·2H₂O] (2), [Cu₂L³(N₃)₂·2H₂O] (3), [Cu₂L⁴(N₃)₂·2H₂O] (4) and [Cu₂L⁵(N₃)₂·2H₂O] (5) of Robson type macrocyclic Schiff-base ligands derived from [2 + 2] condensation of 4-methyl-2,6-diformylphenol with 1,3-diaminopropane (H₂L¹), 1,2-diaminoethane (H₂L²), 1,2-diaminopropane (H₂L³), 1,2-diamino-2-methylpropane (H₂L⁴) and 1,2-diaminocyclohexane (H₂L⁵), respectively have been synthesized and characterized. Catecholase activity of those complexes using 3,5-di-tert-butylcatechol as substrate has been investigated in two solvents, methanol and acetonitrile. The role of the solvent and of the steric properties of the macrocyclic ligand of these complexes on their catecholase activity has been examined thoroughly. Acetonitrile is observed to be a better solvent than methanol as far as their catalytic activity is concerned. However, methanol reveals to be a better choice to identify the enzyme–substrate adduct. The investigation also prompted that chelate ring size does affect on the catalytic efficiency: 6-membered ring (as in H₂L¹) exhibits better activity than its 5-membered counterpart (as in H₂L²). The activity of the 5-membered counter parts also depend upon the steric factor. Moreover, the catalytic activity of the complexes is enhanced to a significant extent by increasing the bulkiness of the substituents on the backbone of macrocyclic H₂L² ligands.     

Chloro-bridged complexes of copper(II) and manganese(II) derived from unsymmetric bidentate ligands: synthesis,crystal structure and characterization

Two new usymmetric bidentate Schiff-base ligands (2-pyridyl-2-furylmethyl)imine (L1) and (2-pyridyl-phenylmethyl)imine (L2) were prepared. The crystal structures of two chloro-bridged complexes [Cu₂(μ-Cl)₂(L1)₂Cl₂] (1) and [Mn (μ-Cl)₂(L2)] (2) derived from the each ligand have been confirmed by single-crystal X-ray diffraction analysis. The complexes were characterized by IR, elemental analysis and spectroscopic methods. In complex 1, the two copper atoms are five-coordinate involving a square-pyramidal geometry having a N₂Cl₃ donor set with the two chlorine atoms bridging the two copper atoms. In complex 2, the manganese atoms are both six-coordinate. In contrast to 1, all chlorine atoms in 2 are bridging chlorides and link adjacent manganese atoms together forming 1-D infinite chains.     

Neutral pyridylmethylamide ligands and their mononuclear copper(II) complexes

Mononuclear copper(II) complexes of a family of pyridylmethylamide ligands HL, HL^Me, HL^Ph, HL^Me3 and HL^Ph3, [HL = N-(2-pyridylmethyl)acetamide; HL^Me = N-(2-pyridylmethyl)propionamide; HL^Ph = 2-phenyl-N-(2-pyridylmethyl)acetamide; HL^Me3 = 2,2-dimethyl-N-(2-pyridylmethyl)propionamide; HL^Ph3 = 2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide], were synthesized and characterized. The reaction of copper(II) salts with the pyridylmethylamide ligands yields complexes [Cu(HL)₂(OTf)₂] (1), [Cu(HL^Me)₂](ClO₄)₂ (2), [Cu(HL)₂Cl]₂[CuCl₄] (3), [Cu(HL^Me3)₂(THF)](OTf)₂ (4), [Cu(HL^Me3)₂(H₂O)](ClO₄)₂ (5a and 5b), [Cu(HL^Ph3)₂(H₂O)](ClO₄)₂ (6), [Cu(HL)(2,2′-bipy)(H₂O)](ClO₄)₂ (7), and [Cu(HL^Ph)(2,2′-bipy)(H₂O)](ClO₄)₂ (8). All complexes were fully characterized, and the X-ray structures vary from four-coordinate square-planar, to five-coordinate square-pyramidal or trigonal-bipyramidal. The neutral ligands coordinate via the pyridyl N atom and carbonyl O atom in a bidentate fashion. The spectroscopic properties are typical of mononuclear copper(II) species with similar ligand sets, and are consistent their X-ray structures.     

Acetato and formato copper(II) paddle-wheel complexes with nitrogen ligands

Compounds Cu(AcO)₂(pydz) (1), Cu(HCOO)₂(pymd)_1/2 (2), Cu(AcO)₂(pymd)_1/2 (3), and Cu(AcO)₂(4,4′-bipy)_1/2 (4) were obtained by reactions of Cu(AcO)₂?H₂O and Cu(HCOO)₂ ? 4H₂O with pyridazine, pyrimidine, or 4,4′-bipyridine. In all the studied structures, the paddle-wheel units [Cu₂[µ-RCOO)₄] are present. Coppers show a square pyramidal coordination determined by four oxygens in the equatorial positions and a nitrogen in the axial position. Compound 1 consists of centrosymmetric dimeric molecules. Compounds 2 and 3 instead consist of zig-zag chains of [Cu₂[µ-RCOO)₄] units linked by bridging pyrimidine molecules. The chains run in the (1 0 1) and (1 1 ?2) directions in 2 and 3, respectively. By crystallization of a solution of 4 in chloroform, Cu(AcO)₂(4,4′-bipy)_1/2 ? 1/2CHCl₃ (5) was obtained. It consists of monodimensional chains of [Cu₂(µ-CH₃COO)₄] units linked by bridging 4,4′-bipy molecules. The chains, of two different types, run parallel to the b-axis in the crystal. Two chlorines of each CHCl₃ molecule are close to two oxygens of two parallel chains. The packing can be described as sheets parallel to the (1 0 ?1) plane. Magnetic properties and electron paramagnetic resonance spectra have been studied.     

Ternary copper(II) complexes of aroylhydrazones and mono/bidentate heterocycles with different structures: synthesis,crystal structure and properties

Two mixed-ligand Cu(II) complexes, [CuL¹(Himdz] · CH₃OH (1) and [CuL²(phen)] · 0.5DMF (2), with different structures have been synthesized by using substituted aroylhydrazones, 5-bromo-salicylaldehyde-benzoylhydrazone (H₂L¹) and 5-bromo-salicylaldehyde-3,5-dimethoxy-benzoylhydrazone (H₂L²), and mono/bidentate heterocycles, imidazole (Himdz) and 1,10-phenanthroline (phen). Their crystal structures and spectroscopic properties have been studied. X-ray analysis show a distorted square-planar geometry for 1 and a distorted square-pyramidal geometry for 2, in which the chelating phen ligand displays axial-equatorial bonding. In both structures the ONO tridentate ligand occupies the basal plane. Self-assembly via O–H ··· N, N–H ··· O and C–H ··· O interactions lead to one-dimensional chain arrangement in 1 and 2.     

Synthesis and properties of the copper(Ⅱ) complexes with stable radical

Four novel copper(Ⅱ) complexes have been synthesized,namely Cu(hfac)2NITPhNO2 (1),Cu(hfac)2NITPhCH3 (2),Cu(pfpr)2NITPhNO2,(3) and Cu(Pfpr)2NITPhCH3 (4),where hfac= hexafluoro-acetylacetonate,pfpr=pentafluoropropionate,NITR.=2-R-4,4,5,5-tetraniethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide.(R=4-nitrophenyl,4-methylphenyl).These complexes were rharicter-ized by elemental analyses,IR,electronic spectra and molar conductance.The temperature-dependent magnetic susceptibility of complexes 1 and 3 have been studied in the 4 300 K range,giving I he exchange integral J=10.56 cm-1 for complex 1 and J =-30.9 cm-1 for complex 3.     

Thermal kinetic TG-analysis of the mixed-ligand copper(II) and nickel(II) complexes of N-(1-phenyl-3-methyl-4-benzylidene-5-pyrazolone) p-nitrobezoylhydrazide and pyridine

Thermal behaviors of three mixed-ligand complexes, [Ni(PMBP-PNH)(Py)₃], [Ni(PMBP-PNH)Py] and [Cu(PMBP-PNH)Py] (PMBP-PNH = N-(1-phenyl-3-methyl-4-benzylidene-5-pyrazolone) p-nitrobezoylhydrazide; Py = pyridine), were studied by TG and DTG in dynamic air atmosphere. The complexes show the loss of pyridine molecule which is followed by the decomposition of the PMBP-PNH anion and give respective metal oxides as residues. Meanwhile, the Ozawa-Flynn-Wall model-free analyses and multivariate non-linear regression were applied to perform single and overall steps optimization. Kinetic parameters were given and the most probable mechanism functions were suggested in this study.