Electrochemical behaviour of zinc(II) and nickel(II) p-diethylaminodithiobenzoate complexes a new nickel(IV) species

The electrochemical behaviour at a platinum electrode in methylene chloride of zinc(II) and nickel(II) p-diethylaminodithiobenzoate complexes has been studied. For the zinc(II) complex the electroactive site of oxidation is the ligand and the tetrathian dication is produced. In contrast, for the nickel(II) complex the electroactive site is the metal and a stable nickel(IV) species is obtained.     

Copper(II), nickel(II), and zinc(II) complexes with <Emphasis Type="Italic">o</Emphasis>-tozylaminobenzaldehyde 4,6-dimethylpyrimidyl hydrazone

o-Tosylaminobenzaldehyde dimethylpyrimidyl hydrazone and its copper(II), nickel(II), and zinc(II) complexesare synthesized and studied. According to the X-ray diffraction data, the zinc(II) complex has the structure of a tetragonal pyramid with the N₃O donor ligand environment. According to EPR and magnetochemistry data, the copper(II) complex has a similar structure of the chelate core. In the nickel(II) complex, the solvent molecule completes the coordination core to an octahedron.     

Mixed-ligand complexes of zinc(II), cobalt(II) and cadmium(II) with sulfur, nitrogen and oxygen ligands. Analysis of the solid state structure and solution behavior. Implications for metal ion substitution in alcohol dehydrogenase

In this paper we characterize new, mixed ligand complexes of zinc(II), cobalt(II) and cadmium(II) with tri-tert-butoxysilanethiolate and 2-(2′-hydroxyethyl)pyridine ligands. Due to the chelating versus non-chelating behavior of 2-(2′-hydroxyethyl)pyridine ligand we have obtained an interesting structural variety in the studied system. The presented coordination patterns together with the results of NMR studies have been used to illustrate a rapid chemical exchange undergoing in methanolic solutions of zinc(II) and cadmium(II) complexes. UV-Vis spectra of cobalt(II) species have also evidenced an exchange in the case of cobalt(II) complex. The relative strength of hydrogen bond formed by hydroxyl group bonded to Zn(II), Co(II) or Cd(II) was evaluated by analysis of structural parameters and position of the OH stretching vibrations in the FT-IR spectra of the complexes in solid state. The data were compared with the activity of zinc (native) alcohol dehydrogenase and alcohol dehydrogenase substituted with cobalt and cadmium ions. The enthalpies of proton abstraction in zinc and cobalt complexes were calculated and found to be very similar. The attempt to apply zinc tri-tert-butoxysilanethiolate as a catalyst in the biomimetic reaction of reduction of N-benzylnicotinamide chloride by ethanol was unsuccessful.     

The thermodynamic characteristics of formation of mono-and binuclear biladiene Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) chelates in dimethylformamide solutions

The spectral and calorimetric data on complex formation between alkyl substituted a,c-biladiene and Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) acetates in dimethylformamide are discussed. The stability of mononuclear biladiene chelates was shown to be determined by steric factors characterizing the formation of coordination polyhedra with the tetradentate ligand. The thermodynamic characteristics of the differential polychelate effect caused by the replacement of the bidentate dipyrrolylmetene ligand with the tetradentate biladiene anion in mononuclear zinc(II) complexes were estimated. The results showed that the largest contribution to the polychelate effect was made by the enthalpy component of the Gibbs energy.     

Synthesis and crystal structure of Isotrithionedithiolato-bis(phenanthroline)zinc(II)

The synthesis of a mixed-ligand complex 1,3-dithiole-2-thione-4,5-dithiolato-bis(1,10-phenanthroline)zinc(II), [Zn(Dmit)(Phen)₂], is described. The crystals are monoclinic, space group P2₁/n, a = 11.868(2) Å, b = 13.122(3) Å, c = 17.010(3) Å, β = 102.01(3)°, Z = 4. The coordination polyhedron of the Zn(II) atom is an octahedron formed by two sulfur atoms of the Dmit ligand and four nitrogen atoms of the two Phen ligands. The complex is studied by IR and UV spectroscopy.     

Syntheses and crystal structures of nickel(II), copper(II), and zinc(II) complexes with a biphenyl-bridged bis(pyrrole-2-yl-methyleneamine) ligand

The reactions of nickel(II), copper(II), and zinc(II) acetate salts with a potentially tetradentate biphenyl-bridged bis(pyrrole-2-yl-methyleneamine) ligand yielded three complexes with different coordination geometries. X-ray crystal structural analysis reveals that in the nickel(II) complex each nickel is five-coordinate, distorted trigonal bipyramid. In the copper(II) complex, each copper is four-coordinate, between square planar and tetrahedral. In the zinc(II) complex, each zinc is four-coordinate with a distorted tetrahedral geometry and the molar ratio of the zinc and ligand is 1 : 2.     

Syntheses and structures of isoindoline complexes of Zn(II) and Cu(II): an unexpected trinuclear Zn(II) complex

Deprotonation of the tridentate isoindoline ligand 1,3-bis[2-(4-methylpyridyl)imino]-isoindoline, 4'-MeLH, and reaction with hydrated zinc(II) perchlorate produces an unexpected trinuclear Zn(II) complex, [Zn(3)(4'-MeL)(4)](ClO(4))(2).5H(2)O (1), whereas reaction with hydrated copper(II) perchlorate in methanol produces the expected mononuclear product, [Cu(4'-MeL)(H(2)O)(2)]ClO(4) (2). X-ray diffraction shows that the trinuclear Zn(II) complex (1) contains a linear zinc backbone, and the arrangement of ligands about the outer chiral zinc(II) atoms is helical. The two terminal zinc ions exhibit approximate C(2) site symmetry, with tetrahedral coordination by two pyrrole and two pyridyl nitrogen atoms of the potentially tridentate isoindoline ligands. The central zinc ion exhibits approximate tetrahedral symmetry, with coordination by four pyridyl nitrogen atoms of four different isoindoline ligands. Pyridyl-pyrrole intramolecular pi-stacking interactions contribute to the stability of the trinuclear cation. The structure of the mononuclear copper(II) complex cation in 2 is best described as a distorted trigonal bipyramid. The isoindoline anion binds Cu(II) in both axial positions and one of the equatorial positions; water molecules occupy the other two equatorial positions.     

Oxidative degradation of beta-diketiminate ligand in copper(II) and zinc(II) complexes

Copper(II) and zinc(II) complexes supported by a popular beta-diketiminate ligand (1(-), 2-mesitylamino-4-mesitylimino-2-pentene), [CuII(1)(AcO)] and [[ZnII(1)]2(mu-MeO)(mu-AcO)], have been demonstrated to undergo an oxidative degradation to give a ketone diimine derivative (2) under aerobic conditions. The crystal structures of the mononuclear copper(II) and dinuclear zinc(II) complexes of the beta-diketiminate ligand as well as the copper(II) complex of the modified ligand have been determined by X-ray crystallographic analysis. Mechanism for the oxidative degradation reaction of the beta-diketiminate ligand is also discussed.     

Thermodynamic and biodistribution studies of Zn(II), Ca(II), Gd(III) and Cu(II) complexes of 3,3,9,9-tetramethyl-4,8-diazaundecane-2,10-dione dioxime

The thermodynamic equilibria of copper(II), zinc(II), calcium(II) and gadolinium(III) with 3,3,9,9-tetramethyl-4,8-diazaundecane-2,10-dione dioxime (L1) have been studied at 25 degrees C and an ionic strength of 0.15 mol dm(-3). Copper and gadolinium form stable complexes with the ligand while the corresponding zinc species are more than 9 log units less stable. No complexes between calcium and the ligand were detected. The low binding strength of L1 towards zinc is attributed to the square-planar coordination geometry forced on the metal ion by the ligand as revealed by molecular mechanics calculations and molecular dynamics simulations. Speciation calculations, using a computer model of blood plasma, indicate that, despite the high concentration of zinc(II) and calcium(II) in vivo, L1 is able to increase the low-molecular-mass fraction of copper in plasma. Octanol/water partition coefficient of [CuL1H(-1)] indicates that although this species is largely hydrophilic, approximately 6% of the complex goes into the octanol phase and hence may promote dermal absorption of copper by the same amount. The dermal penetration rate is calculated to be 4.0 x 10(-4) mm h(-1). The [CuL1H(-1)] complex, which predominates at pH 7.4, is a poor mimic of native copper-zinc superoxide dismutase. Biodistribution experiments using the 64Cu-labelled [CuL1H(-1)] complex indicate an initial high uptake of this species in the liver followed by redistribution into muscle. Only a small amount is excreted through the urine.     

Novel repaglinide complexes with manganese(II), iron(III), copper(II) and zinc(II): Spectroscopic,DFT characterization and electrochemical behaviour

Novel transition metal complexes with the repaglinide ligand [2-ethoxy-4-[N-[1-(2piperidinophenyl)-3-methyl-1-1butyl] aminocarbonylmethyl]benzoic acid] (HL) are prepared from chloride salts of manganese(II), iron(III), copper(II), and zinc(II) ions in water-alcoholic media. The mononuclear and non-electrolyte [M(L)₂(H₂O)₂]?nH₂O (M = Mn²⁺, n = 2, M = Cu²⁺, n = 5 and M = Zn²⁺, n = 1) and [M(L)₂(H₂O)(OH)]?H₂O (M = Fe³⁺) complexes are obtained with the metal:ligand ratio of 1:2 and the L-deprotonated form of repaglinide. They are characterized using the elemental and molar conductance. The infrared, ¹H and ¹³C NMR spectra show the coordination mode of the metal ions to the repaglinide ligand. Magnetic susceptibility measurements and electronic spectra confirm the octahedral geometry around the metal center. The experimental values of FT-IR, ¹H, NMR, and electronic spectra are compared with theoretical data obtained by the density functional theory (DFT) using the B3LYP method with the LANL2DZ basis set. Analytical and spectral results suggest that the HL ligand is coordinated to the metal ions via two oxygen atoms of the ethoxy and carboxyl groups. The structural parameters of the optimized geometries of the ligand and the studied complexes are evaluated by theoretical calculations. The order of complexation energies for the obtained structures is as follows:

$$Fe(III) complex < Cu(II) complex < Zn(II) complex < Mn(II) complex.$$

The redox behavior of repaglinide and metal complexes are studied by cyclic voltammetry revealing irreversible redox processes. The presence of repaglinide in the complexes shifts the reduction potentials of the metal ions towards more negative values.

     

Bioactive Co(II), Ni(II), and Cu(II) Complexes Containing a Tridentate Sulfathiazole-Based (ONN) Schiff Base

New Co(II), Ni(II), and Cu(II) complexes were synthesized with the Schiff base ligand obtained by the condensation of sulfathiazole with salicylaldehyde. Their characterization was performed by elemental analysis, molar conductance, spectroscopic techniques (IR, diffuse reflectance and UV–Vis–NIR), magnetic moments, thermal analysis, and calorimetry (thermogravimetry/derivative thermogravimetry/differential scanning calorimetry), while their morphological and crystal systems were explained on the basis of powder X-ray diffraction results. The IR data indicated that the Schiff base ligand is tridentate coordinated to the metallic ion with two N atoms from azomethine group and thiazole ring and one O atom from phenolic group. The composition of the complexes was found to be of the [ML₂]∙nH₂O (M = Co, n = 1.5 (1); M = Ni, n = 1 (2); M = Cu, n = 4.5 (3)) type, having an octahedral geometry for the Co(II) and Ni(II) complexes and a tetragonally distorted octahedral geometry for the Cu(II) complex. The presence of lattice water molecules was confirmed by thermal analysis. XRD analysis evidenced the polycrystalline nature of the powders, with a monoclinic structure. The unit cell volume of the complexes was found to increase in the order of (2) < (1) < (3). SEM evidenced hard agglomerates with micrometric-range sizes for all the investigated samples (ligand and complexes). EDS analysis showed that the N:S and N:M atomic ratios were close to the theoretical ones (1.5 and 6.0, respectively). The geometric and electronic structures of the Schiff base ligand 4-((2-hydroxybenzylidene) amino)-N-(thiazol-2-yl) benzenesulfonamide (HL) was computationally investigated by the density functional theory (DFT) method. The predictive molecular properties of the chemical reactivity of the HL and Cu(II) complex were determined by a DFT calculation. The Schiff base and its metal complexes were tested against some bacterial strains (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis). The results indicated that the antibacterial activity of all metal complexes is better than that of the Schiff base.     

Three-ring, branched cyclam derivatives and their interaction with nickel(II), copper(II), zinc(II) and cadmium(II)

The interaction of two symmetrically branched tris-cyclam derivatives based on 1,3,5-trimethylenebenzene and phloroglucinol cores with nickel(II), copper(II), zinc(II) and cadmium(II) is reported. All four metal ions yield solid complexes in which the metal : ligand ratio is 3 : 1. For both ligand types, spectrophotometric titrations confirm the formation of nickel(II) and copper(II) complexes of similar 3 : 1 stoichiometry in dimethyl sulfoxide. Visible spectral, electrochemical, magnetic moment, ESR and NMR studies have been performed to probe the nature of the respective complexes. Where appropriate, the results from the above metal-ion studies are compared with those from parallel investigations in which the corresponding (substituted) mono-cyclam analogues were employed as the ligands. A structural determination employing a poorly diffracting crystal of the trinuclear nickel(II) complex of the tris-cyclam ligand incorporating a 1,3,5-trimethylenebenzene core was successfully carried out with the aid of a synchrotron radiation source. A nickel ion occupies each cyclam ring in a square-planar coordination arrangement, with each cyclam ring adopting the stable trans-III configuration.     

Synthesis,Crystal Structure,Antioxidation and DNA‐Binding Studies of a Zinc(II) Complex with the Bis(N‐allylbenzimidazol‐2‐ylmethyl)aniline

A complex of zinc(II) picrate (pic) with bis(N‐allylbenzimidazol‐2‐ylmethyl)aniline (abba), with composition [Zn(abba)₂](pic)₂, was synthesized and characterized by elemental analysis, electrical conductivity, IR and UV/Vis spectral measurements. The crystal structure of the zinc(II) complex has been determined by single‐crystal X‐ray diffraction. The Zn(II) is bonded to two abba ligands through four benzimidazole nitrogen, resulting in a distorted tetrahedron geometry. The DNA‐binding properties of the ligand and the zinc(II) complex were investigated by electronic absorption, fluorescence spectra and viscosity measurements. The experimental results suggest that the zinc(II) complex binds to DNA in an intercalation mode. In addition, the ligand abba and Zn(II) complex have scavenging effects for hydroxyl radicals and the complex shows stronger scavenging effects for hydroxyl radicals than the ligand.     

Solution studies of tris(2-benzylaminoethyl)amine complexes of zinc(II) and copper(II): The catalytic hydrolysis of toxic organophosphate

Solution studies of the tetradentate ligand tris(2-benzylaminoethyl)amine, BzTren with both zinc(II) and copper(II) salts were investigated in aqueous methanol (33% v/v) by means of ¹H NMR, potentiometric, and UV-visible titrations as well as cyclic voltammetry. Subsequently, their zinc(II) and copper(II) complexes [BzTren-M(OH₂)]²⁺ 1 and 2 (M²⁺ = Zn²⁺ and Cu²⁺) were synthesized and fully characterized by using FT-IR spectroscopy, elemental analysis, and thermal analysis. Complexes 1 and 2 are investigated kinetically for the catalytic hydrolysis of the toxic organophosphate parathion at 50 °C in aqueous methanol (33%, v/v). The kinetic results indicate that copper(II) complex 2 is more active than zinc(II) complex 1, presumably a reflection of the effective electron-withdrawing as well as the greatest electrophilicity of copper(II) ion.     

Copper(II) and zinc(II) complexes with terpene derivatives of ethylenediamine: unexpected ligand transformations

Crystallization of copper and zinc complexes with imino terpene derivatives of ethylenediamine causes unexpected chemical transformation of the ligand. Copper(II) chloride catalyzes the hydrolysis of the imine and also acts as a halogenating agent. Crystallization of the zinc complex in acetone is accompanied by the condensation of the ketone with the primary amino group of the ligand.     

A novel vic-dioxime ligand and its Ni(II), Cu(II) and Co(II) complexes containing calix[4]pyrrole moiety: synthesis, characterization and redox properties

A new calix[4]pyrrole functionalized vic-dioxime, 3-(4-methyl-9,9,14,14,19,19-hexaethylcalix[4]pyrrole)benzoaminoglyoxime (LH₂) was synthesized from anti-chloroglyoxime and 3-aminophenyl-calix[4]pyrrole at room temperature. The mononuclear complexes {nickel(II), copper(II) and cobalt(II)} of this vic-dioxime ligand were prepared and their structures were confirmed by elemental analysis, IR and UV–Vis spectrophotometry, magnetic susceptibility; the MS, ¹H and ¹³C NMR spectra of the LH₂ ligand and its Ni(II) complex were also recorded. The experimental results indicated that the ligand:metal ratio was 2:1 in the cases of Ni(II), Cu(II) and Co(II) complexes as is with most vic-dioximes. Electrochemical properties of the ligand, and its complexes were investigated in DMSO solution by cyclic voltammetry at 200?mV?s^?1 scan rate.     

Thermal decomposition of mixed ligand complexes of cobalt(II), nickel(II), zinc(II) and cadmium(II) containing 1,3-diaminopropan-2-ol and oxalate

Non-isothermal kinetics of the thermal decomposition of mixed ligand complexes of cobalt(II), nickel(II), zinc(II) and cadmium(II) have been studied using thermogravimetry (TG) and differential scanning calorimetry (DSC). The reaction in which the complex loses one molecule of the ligand is found to be first order and the activation energy was calculated using established techniques. Using Dharwadkar and Karkhanavala's method, the values obtained were 25.65, 17.32, 25.22 and 20.95 kcal mole^?1, respectively. Infrared spectral studies of these complexes and intermediates provided information regarding the coordinating nature of the ligand 1,3-diaminopropan-2-ol in these complexes.     

Synthesis,thermal, spectral and biological properties of zinc(II) 4-hydroxybenzoate complexes

New zinc(II) 4-hydroxybenzoate complex compounds with general formula [Zn(4-OHbenz)₂L_n]·xH₂O, where 4-OHbenz = 4-hydroxybenzoate; L = isonicotinamide, N-methylnicotinamide, N,N-diethylnicotinamide, thiourea, urea, phenazone, theophylline, methyl-3-pyridylcarbamate; n = 2, 3; x = 0–3, 5, were synthesized and characterised by elemental analysis, thermal analysis and IR spectroscopy. The thermal behaviour of the prepared compounds was studied by TG/DTG and DTA methods in argon atmosphere. The thermal decomposition of hydrated compounds started with dehydration. During the thermal decomposition, organic ligand, carbon monoxide, carbon dioxide and phenol were evolved. The final solid product of the thermal decomposition was zinc or zinc oxide. The volatile gaseous product, solid intermediate products and the final product of thermal decomposition were identified by IR spectroscopy, mass spectrometry, qualitative chemical analyses and X-ray powder diffraction method. The antimicrobial activity of zinc(II) carboxylate compounds was tested against various strains of bacteria, yeasts and filamentous fungi (S. aureus, E. coli, C. parapsilosis, R. oryzae, A. alternata, M. gypseum). The presence of zinc in complexes led to the increase in their antimicrobial activity in comparison with free 4-hydroxybenzoic acid.     

Synthesis and characterization of cobalt(II) and zinc(II) complexes of poly(3-nitrobenzyli dene-1-naphthylamine-co-succinic anhydride)

The cobalt(II) and zinc(II) complexes of poly(3-nitrobenzylidene-1-naphthylamine-co-succinic anhydride) were synthesized by the reaction of THF solution of the alternating copolymer with aqueous solution of cobalt(II) and zinc(II) acetates. The metal complexes were characterized by elemental analysis, magnetic measurements, IR, UV–Vis. and ¹H NMR spectral studies. The elemental analysis of the metal polymer complexes suggests that the metal to ligand ratio is 1:2. Conductance measurements indicate the non electrolytic nature of both the complexes. Electronic spectrum and magnetic moment studies are taken into account for the geometry of cobalt complex. Thermal analysis data of the two metal–polymer complexes were reported. XRD data revealed the nanocrystalline nature of both the complexes. The SEM studies give the surface morphology of the complexes.     

Complexation Equilibria of Zn(II), Pb(II) and Cd(II) with Reduced Glutathione (GSH) and Biologically Important Zwitterionic Buffers

The interaction of zinc(II), lead(II), and cadmium(II) with Glutathione (S‐L‐glutamyl‐Lcysteinylglycine) as primary ligand and zwitterionic buffers (N‐[2‐Hydroxyethyl]piperazine‐N′‐[2‐ethanesulfonic acid]) (HEPES) and (N‐Hydroxyethyl]piperazine‐N′‐[2‐hydroxy‐propanesulfonic acid]) (HEPPSO) as secondary ligands were studied by potentiometric‐pH titration in 1:1:1 ratio at 25.0 °C and I = 0.1 mol.dm^?3 (KNO₃). The formation constants of different normal and protonated binary and ternary complex species were calculated. Formation constants for the monohydroxy, and dihydroxy complexes for the binary systems M(II) + HEPES and M(II) + HEPPSO have been evaluated. The distribution curves for the various complex species as a function of pH were constructed.