A polarographic study of the mixed complexes of Pb(II) with oxalate and malonate ions

The coordinated mixed Pb(II)-oxalate-malonate system has been polarographically studied in aqueous medium. The ionic strength has been maintained constant at μ = 1.0 by using NaClO₄. Application of the Schaap and McMasters method detected only the existence of the [Pb-ox-mal]_2? complex, the overall stability constant of which was β₁₁ = 4.1 x 10⁵.The various coordination equilibria are discussed on the basis of statistical aspects.     

Potentiometric investigation mixed ligand complexes of Ni(II) with DL-methionine and Dl-ethionine in aqueous solution

The formation of mixed ligand complexes of Ni(II) with DL-methionine in aqueous solution was investigated. The composition and stability constants of the complexes were determined by the potentiometric method.     

Synthesis and spectral studies of mixed copper(II) dipeptide complexes of imidazole and related nitrogen donors

Eight mixed copper(II) complexes of the type [Cu(II)(D)(HL)], where D = anion of glycylglycine, glycyl-L-tyrosine or glycyl-L-phenylalanine, and HL = imidazole, 1-methylimidazole, 2-methylimidazole or benzimidazole have been prepared and characterised. The visible and EPR spectral studies of these complexes indicate that they are monomeric having five coordinate square pyramidal geometry (possibly distorted) about Cu(II). The dipeptide behaves as terdentate ligand in these complexes with amino, ionised amide nitrogen and carboxylate oxygen donor atoms approximately tetragonally disposed about Cu(II). The magnetic and bonding parameters obtained by detailed EPR spectral analysis coupled with electronic absorption spectral data suggest that imidazole, 1-methylimidazole, 2-methylimidazole or benzimidazole occupies the fourth position in the tetragonal plane and water molecule occupies an axial position about Cu(II) in solid state and in solution.     

Comparative study of hydroxo-fluoro and hydroxo-sulphido mixed ligand complexes of aluminum(III) and gallium(III)

The mixed ligand complex formation had been studied in the aluminate-fluoride, gallate-fluoride, aluminate-sulphide and gallate-sulphide systems by spectrophotometric as well as potentiometric methods using glass and sulphide selective electrodes. The formation of the species Al(OH)₃F^? and Ga(OH)₂S^? has been demonstrated and the equilibrium constants have been determined. Similar interaction could not be detected in the aluminate-sulphide and gallate-fluoride systems.The differences in behaviour of the metal ions to the characteristically hard fluoride and soft sulphide ligands can be interpreted in that the Ga³⁺ ion may form complexes with charged soft ligands too, its behaviour then differing from that of the typically hard Al³⁺ ion.     

Formation and thermodynamic properties of mixed complexes of Cd(II) with thiourea and nitrite or thiosulphate ions as ligands

Formation and thermodynamic parameters of mononuclear mixed complexes Cd(SCN₂H₄)_n(NO₂)^2?p_p and Cd(SCN₂H₄)_n(S₂O₃)^2(1?p_p in aqueous solution were investigated by potentiometric measurements at different temperatures and μ = 1 for KNO₃.     

Polarographic study of Eu(III)-succinate-ethylenediamine and Eu(III)-malonate-ethylenediamine mixed systems

The mixed complexes of Eu(III) with succinate (succ^2?) and malonate (mal^2?) and ethylenediamine (en) have been studied polarographically at 25°C and at constant ionic strength, μ = 0.1 (NaNO₃) and pH 6. The reduction of the complexes in each case is quasi-reversible and diffusion-controlled. In each system three mixed complexes are formed, viz. [Eu(succ)(en)]⁺, [Eu(succ)(en)2]⁺ and [Eu(succ)₂(en)]^? with stability constants log β₁₁ = 9.2, log β₁₂ = 17.5 and log β₂₁ = 11.7; and [Eu(mal)(en)]⁺, [Eu(mal)₂(en)₂]^? and [Eu(mal)₃(en)]^3? with stability constants log β₁₁ = 11.4, log β₂₂ = 19.08 and log β₃₁ = 13.5 respectively.     

Polarographic study of Sn(IV) chloride-pyridine N-oxide complexes in acetonitrile

Polarograms recorded of Sn(IV) chloride in acetonitrile in the presence of controlled quantities of each of nine substituted pyridine N-oxide ligands demonstrated the formation of stable and soluble complexes with a stoichiometry dependent upon the nature and position of the ring substituent. The polarographic data associated with each complex and the free ligands are used to substantiate a proposed bonding model which explains the dependency of the complex formula on the ligand structure. The salt SnCl₄·5H₂O was employed as a source of Sn(IV) and the complete polarographic behaviour of this salt in acetonitrile is described as a basis for the interpretation of complex reduction behaviour.     

Synthesis and characterization of mixed ligand complexes of copper(II), nickel(II), cobalt(II) and zinc(II) with glycine and uracil or 2-thiouracil

Mixed ligand complexes of Cu(II), Ni(II), Co(II) and Zn(II) formed with glycine and uracil or 2-thiouracil have been synthesized and characterized by elemental analysis, conductance, spectral (IR and electronic spectra) and magnetochemical measurements. Results show that glycine is bidentate in all cases; uracil behaves as a bidentate ligand in Cu(II) complex, coordinating through its one carbonyl oxygen and nitrogen, whereas in other cases it is only monodentate, coordinating only through nitrogen. With thiouracil, coordination occurs from carbonyl oxygen and one nitrogen in Cu(II) and Ni(II) complexes, but in the Co(II) complex coordination occurs from thionyl sulphur and nitrogen. In the Zn(II) complex it shows tridentate behaviour, coordinating through oxygen, sulphur and one nitrogen. Mixed Cu(II), Co(II) and Zn(II) complexes of uracil and of Ni(II) and Zn(II) with thiouracil are octahedral, whereas the mixed Ni(II) complex with uracil shows distorted tetrahedral geometry, and the mixed Co(II)-thiouracil complex is square planar. The mixed Cu(II)-thiouracil complex has a binuclear structure, with square planar arrangement around each copper atom.     

A study of mixed ligand complexes using differential pulse polarography

Differential pulse polarography was used to study the mixed ligand complexes of trimethylenediamine (TMDA) and oxalate (OX) with Cd(II) at constant ionic strength (μ = 1, NaNO₃) at 25°C. It has been found that the reduction of complexes is reversible and diffusion-controlled. Three mixed complexes, [Cd(TMDA)(OX)], [Cd(TMDA)(OX)₂]^2? and [Cd(TMDA)₂(OX)], are formed. Their overall stability constants are: log β₁₁ = 6.78, log β₁₂ = 7.53 and log β₂₁ = 8.20, respectively.     

An NMR study of the complexes of Zn(II) and Cd(II) ions with tris(dimethylamino)phosphine sulphide: Ligand exchange kinetics

The preparation of the complex species [Cd(TDPS)₄](ClO₄)₂ and [Zn(TDPS)₄](ClO₄)₂ (TDPS = tris(dimethylamino)phosphine sulphide)     

Four- and five-coordinate copper(II) complexes containing mixed ligands

New copper(II) complexes of general formula, Cu(ONS)B (ONS = the di-negatively charged Schiff base, S-benzyl-β-N-(2-hydroxyphenyl) methylendithiocarbazate; B = pyridine, 2,2′-dipyridyl or 1,10-phenanthroline) have been synthesized and characterised by magnetic and spectroscopic measurements. The complex, Cu(ONS)py is four-coordinate and square-planar. Magnetic and spectroscopic data support a five-coordinate, presumably, a trigonal-bipyramidal structure for the [Cu(ONS)dipy] and (Cu(ONS)phen] complexes     

Inhibitorial effect of the Cu(II) and Ni(II) complexes with polyamines and imidazole derivatives on the Ca,Mg-dependent ATP-ase substrate

The investigation of the inhibitory activity on the Ca,Mg-dependent ATP-ase substrate of some Cu(II) and Ni(II) complexes with polyamines and imidazole derivatives is reported. These results show that the Cu(II) complexes have high inhibitorial effect with the exception of the following very stable compounds: square planar [Cu(N-PropIm)₂(NCS)₂], distorted octahedral [Cu(bipy)₂(NCS)₂] and five coordinate [Cu(Me₆tren)(NCS)] (SCN). The Ni(II) derivatives present a medium inhibitorial activity except to the stable tetrahedral [Ni(N-PropIm)₂(NCS)₂], hexacoordinate [Ni(dpt)(tn)(NCS)] (SCN) and fivecoordinate [Ni(dpt)(tn)]Br₂ and [Ni(Me₆tren)(NCS)] (SCN). An explanation of these conclusions is reported.     

Mixed ligand complexes involved in the system pyridoxamine-glycylglycine-imidazole copper(II)

Ternary as well as quaternary complexes involved in the system pyridoxamine-glycylglycine-imidazole-copper(II) have been studied by pH-metric titration at 37°C and I = 0.15 M (NaNO₃). The data were assessed by program MINIQUAD 75. The formation constants were compared with those obtained from the system of pyridoxamine-glycine-imidazole with some bivalent metal ions previously reported. They are ～ 2.5 log units less. In addition, the enhancement of quaternary complex formation has been described in terms of binary and ternary complex formation reactions. It has been also found that deprotonation of the peptidic proton of glycylglycine took place in the presence of more than one different ligand.     

The preparation and electrochemistry of manganese(II) complexes of an unsaturated pentadentate macrocyclic ligand

The preparation of a series of six and seven coordinate manganese(II) complexes [Mn^(II)(L)X]⁺, and [Mn^(II)(L)X₂]^2? (X = halide, water, triphenylphosphine oxide, imidazole, 1-methyl imidazole and pyridine) incorporating the pentadentate planar macrocylic ligand L is described. Cyclic voltammetry of these complexes in acetonitrile each shows a reversible one-electron reduction wave near - 1.4 V vs a Ag/AgNO₃ reference electrode. Quantitative reduction of these complexes by controlled potential electrolysis at a platinum gauze at - 1.4 V yields the corresponding one-electron reduction products which have been shown by ESR spectroscopy to be manganese(II)-ligand radical species, the electron being thought to reside on the di-imino pyridine moiety of the macrocyclic ligand. No metal reduced species could be isolated even in the presence of π-acceptor ligands such as CO or phosphines.     

Some mixed-ligand palladium(II) complexes and comparison of their photosensitizing ability with analogous platinum(II) complexes

Three new palladium(II) complexes of formula [Pd(bipy)(XX)] [where bipy is 2,2′-bipyridine and XX are dianions of catechol (CAT), 4-tert-butylcatechol (BCAT) and 3,4-dimercaptotoluene (DMT)] have been prepared and characterized by physical methods. A ligand-ligand charge-transfer band in each complex was observed between 16–21 kK (ε_max = 1500–2200 1 mol^?1 cm^?1) which is negatively solvochromic. These palladium(II) complexes in dimethylformamide photosensitize the formation of singlet oxygen and their ability to photosensitize triplet oxygen (³O₂) to singlet oxygen (¹O₂) are compared with analogous platinum(II) complexes. In addition, 2,2′-bipyridine-platinum(II) complex of 3,4-dimercaptotoluene also undergoes self-sensitized photooxidation.     

3,6-bis(2′,-pyridyl)pyridazine dinuclear complexes: Palladium(II), platinum(II) and first row transition metal(II) mixed complexes

New Pd(II) and Pt(II) 3,6-bis(2′-pyridyl)pyridazine (dppn) mononuclear complexes of the type M(dppn)Cl₂ were prepared and characterized. From M(dppn)Cl₂, the bimetallic homonuclear complexes M(dppn)MCl₄ were prepared by reaction with Pd(PhCN)₂Cl₂ or K₂PtCl₄. Bimetallic heteronuclear species of the type M(dppn)M′Cl₄, were prepared reacting the mononuclear complexes with the stoichiometric amount of M′Cl₂ (M′ = Cu, Co, Ni). All the described reaction give product in high yield. The isolated compounds, almost completely insoluble in most organic solvents, were characterized by elemental analysis, IR, ESR, reflectance spectra, and magnetic moment measurements. On the basis of these data the geometries around the metals are discussed.     

Some complexes of nickel (II) with morpholine

The compounds NiX₂M_x[M = morpholine; X = C₆F₅ (x = 2), NO₃(x = 3), Br(x = 2 or 3), and I(x = 4)] have been prepared and investigated. Magnetic and spectral studies have been carried out to determine the mode of coordination and stereochemistry of the complexes. Except for NiBr₂M₃, which appears to contain bridging morpholine, in all other compounds the neutral ligand acts as a monodentate N-donor group.     

Potentiometric studies on mixed complexes of Ni(II) with taurine,dl-methionine and dl-ethionine in aqueous solution

The formation and stability of the simple and mixed complexes of Ni(II) with taurine, dl-methionine and dl-ethionine have been investigated by means of potentiometric measurement of hydrogen ion concentration at 25°C and in a 0.1 M NaClO₄ medium. Mixed complexes, [Ni(Met₂)Tau] and [Ni(Eth₂)Tau], have been considered, where Met = dl-methionine, Eth = dl-ethionine and Tau = taurine.     

Carbonyl-organocobalt(I) and -(II) complexes

Passage of CO through solutions of complexes (C₆F₅)₂CoL₂ gives carbonyl derivatives (C₆F₅)₂CoL₂(CO) (L₂ = 2 PEt₃, 2 P-n-Bu₃, 2 PPh₃, Ph₂PCH₂CH₃PPh₂). The properties of these compounds are described.The compounds are also produced by treating solutions of (C₆F₅)₂Co-(dioxane)₂ with CO, but a simultaneous reduction to (C₆F₅)Co(CO)₄ takes place. Treatment of the latter complex with monodentate ligands gives substitution products (C₆F₅)Co(CO)₃L (L = PEt₃, P-n-Bu₃, PPh₃) all of which are monomeric, whereas the addition of Ph₂PCH₂CH₂PPh₂ gives the dimer (C₆F₅)(CO)₂CoLLCo(CO)₂(C₆F₅). The properties of these compounds are discussed.     

Preparation and characterization of copper(II) and nickel(II) complexes with novel tetraaza-macrocyclic schiff bases

Novel tetraaza-macrocycles with N-substituted carbamoyl groups were prepared by the reaction of 5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,5,7,12-tetraene with isocyanates (RNCO, R = Ch₃ and C₆H₅). Their copper(II) and nickel(II) complexes were characterized by magnetic susceptibilities, electronic absorption spectra, and electrochemical properties. The complexing abilities and extractabilities of the ligands for the metal ions were investigated.