Complex formation in the ternary systems copper(II)/nickel(II)/cobalt(II) - isonicotinic acid hydrazide-L-histidine was studied by the methods of spectrophotometry and mathematical modeling in an aqueous solution with 0.1 mol dm(-3) KNO3 as a background electrolyte. The compositions, formation constants, and spectral parameters of the heteroligand complexes with a metal/hydrazide/amino acid ratio of 1:1:1 were determined. It was found that the heteroligand complexes with the neutral form of isonicotinic acid hydrazide have higher stability values than those with the protonated form. The stability of bis- and tris-complexes of the same composition in the series copper(II) - nickel(II) - cobalt(II) is in agreement with the Irving-Williams order. Three isomers of the heteroligand complex of nickel(II) with the protonated form of isonicotinic acid hydrazide and histidine zwitterion were optimized by the method of molecular mechanics. In the system with cobalt(II), a reversible interaction with atmospheric oxygen was revealed.

Using the methods of pH-metry and mathematical simulation, we studied the complex formation in the copper(II)–malonic (L)/adipic acid (L')–L-histidine (HisH) ternary systems in aqueous medium against 1.0 M KNO3 solution at 25.0°C. The stability constants of (1 : 1 : 1) heteroligand complexes were determined. Quantum chemical calculations of the structures of heteroligand complexes were performed. It was revealed that the Cu(His)(L)+ and Cu(His)(L')+ complexes exist predominantly in the cis-form.

The composition and stability constants of homo- and heteroligand copper(II) complexes with benzoic acid, p-methoxybenzoic acid, or o-hydroxybenzoic acid hydrazide and L-histidine have been determined by spectrophotometry and mathematical modeling methods in aqueous solution with 0.1 M KNO3 as background at 25.0°C. Structural features of some complexes formed in binary and ternary systems have been determined using IR spectroscopy and quantum-chemical calculations.

Complex formation of nickel(II) with benzoic, para-methoxybenzoic acid hydrazides, and L-histidine have been studied by the methods of pH-metric titrimetry, spectrophotometry, and mathematical modelling in aqueous solutions with 1.0 mol dm(-3) KNO3 as background at 298 K. Dissociation constants of ligands, as well as composition, formation constants, and spectral parameters of homo-and heteroligand complexes have been determined. It has been shown that stability of the complexes formed with para-methoxybenzoic acid hydrazide is higher than with benzoic acid hydrazide, which is consistent with the electron-donor properties of the methoxy group. Extra stabilization of the nickel(II) heteroligand complexes with benzoic (para-methoxybenzoic) acid hydrazide and L-histidine has been discovered and interpreted.

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The protolytic and complex formation properties of copper(II) with tetrahydrazide (25,26,27,28-tetrakis[hydrazinocarbonylmethyloxy]calix[4]arene) were studied in water-dimethylsulfoxide media using spectrophotometry, pH-metric titration, and mathematical modeling. The dissociation constants for the protonated forms of the tetrahydrazide and the formation constants for the complexes have been determined. Mono-and polynuclear complexes with molecular and protonated forms of the ligand were observed.

Acid-base and complexing properties of 4-tert-butylphenoxyacetic acid hydrazide, resorcinol acetic acid dihydrazide, and 25,26,27,28-tetrakis[hydrazinocarbonylmethyloxy]-2,8,14,20tetrathiacalix[4] arene have been studied in water-dimethylsulfoxide media (80 vol. %, 0.48 mol) by spectrophotometry, pH-titration, and mathematical modeling. The dissociation constants of the protonated forms of the hydrazides have been determined. The compositions and the formation constants of the complexes with copper(II) and nickel(II) have been calculated. For the monohydrazide, 1 : 1 and 1 : 2 stoichiometry complexes with molecular form of the ligand have been obtained. For the case of resorcinol acetic acid dihydrazide and 25,26,27,28-tetrakis[hydrazinocarbonylmethyloxy]-2,8,14,20-tetrathiacalix[4] arene, complexes with molecular and protonated forms of the ligands as well as dimeric and tetrameric complexes have been characterized. It has been found that the stability of the copper(II) and nickel(II) complexes of similar composition is in agreement with the Irving-Williams series.

Protolytic equilibrium of adipic acid dihydrazide (L) in water-organic media (dimethyl sulfoxide, dimethyl formamide, 1,4-dioxane) with the mole fraction of organic solvent of 0-0.68 was studied using the methods of pH-metric titration and mathematical simulation. Dissociation constants for mono-and diprotonated dihydrazide forms were determined. There is an extreme dependence of pK(a) on the proportion of organic component in water solutions of aprotonic solvents. It is shown that in water-organic media the diprotonated form of dihydrazide is more stabilized compared to the monoprotonated one, the latter being more solvated in relation to the molecular form.

Solvation and complexation of Cu(II), Ni(II), and Co(II) with adipic acid dihydrazide (L) in aqueous and aqueous-ethanol solutions (ethanol mole fraction 0.07–0.68) were studied by spectrophotometry. The formation constants of the species M(LH) 3+ , ML 2+ , M 2 L 4+ (μ = Cu 2+ , Ni 2+ , Co 2+ ), and also M 2 L 2 4+ and ML 2 2+ (μ = Cu 2+ , Ni 2+ ) were determined. With Cu(II), the complexes Cu(LH) 2 4+ , CuL(LH) 3+ , and Cu 2 L(LH) 5+ were also detected and characterized. Evidence is given for the hydrazide coordination mode: tridentate in ML 2+ , bidentate in M(LH) 3+ and ML 2 2+ , and tetradentate in M 2 L 4+ and M 2 L 2 4+ . The ligand exchange reactions involving CuL 2+ , Cu(LH) 3+ , Cu(LH) 2 4+ , CuL(LH) 3+ , CuL 2 2+ , and Cu 2 L(LH) 5+ in aqueous solutions of Cu(II) were revealed and kinetically characterized by nuclear magnetic relaxation. The heretofore unknown rate constants of formation of these complexes were calculated from the thermodynamic and kinetic parameters. Factors controlling the rate constants of the complex formation and chemical exchange are discussed.

Solvation and complexation of Cu(II) and Ni(II) with benzoic (L′), p-methoxybenzoic (L″), and isonicotinic (L) acid hydrazides in aqueous-ethanol solutions (ethanol mole fraction 0.07–0.68) were studied by pH-metry, spectrophotometry, and nuclear magnetic relaxation. The formation constants of the species M(L′)2+, M(L′) 2 2+ , M(L″)2+, M(L″) 2 2+ , M(LH)3+, M(L)2+, M(L)(LH)3+, and M(L) 2 2+ , where M = Cu2+ and Ni2+, were determined. With isonicotinic acid hydrazide, a change in the coordination mode was observed in an isomer of Cu(L) 2 2+ , with one of the ligands coordinating in the bidentate fashion, and the other, in the monodentate fashion via the pyridine nitrogen atom. The suggested structures were confirmed by analysis of the parameters of the ESR and electronic absorption spectra of the complexes. The rate constants of ligand exchange and formation of the complexes Cu(L′)2+, Cu(L′) 2 2+ , Cu(L″)2+, and Cu(L″) 2 2+ in aqueous solutions were determined from nuclear magnetic relaxation measurements; the reactions occur by the associative mechanism. A cyclic process of reduction of Cu(II) to colloidal copper in the presence of L″ and atmospheric oxygen is described.

Solvation and complex formation of nickel(II) with benzoic, p -chlorobenzoic, and p -methoxybenzoic hydrazides in aqueous-dioxane media were studied. The mean coordination numbers of water and 1,4-dioxane in Ni(II) solvation complexes, the formation constants of mono- and biscomplexes of nickel(II) of the listed hydrazides at dioxane contents of 0-0.65 mole fraction, as well as the free energies of transfer of the ligands from water to aqueous-dioxane solvents were determined. An important role the basicity and solvation of the ligands play in te stability of Ni(II) complexes with benzoic hydrazides was demonstrated.

Solvation and complexation of Ni(II) with benzoic (L1), p-methoxybenzoic (L3), and isonicotinic (L) acids hydrazides in water and aqueous acetonitrile were studied. The coordination of acetonitrile with Ni(II) was qualitatively estimated, and the formation constant were determined for the complexes Ni(L1)2+, Ni(L1)22+, Ni(L3)2+, Ni(L3)22+, Ni(HL)3+, NiL2+, NiL(HL)3+, and NiL22+. The effects of dilution, ligand basicity, and ligand solvation on the stability of Ni(II) compounds with hydrazides of benzoic acid and its derivatives were demonstrated. The stability of the Ni(II) complexes with isonicotinic acid hydrazide is governed by dehydration of the metal ion, decrease in the donor power of the coordinating hydrazide fragment on protonation of the pyridine substituent L, formation of the intracomplex hydrogen bond between the protonated and deprotonated pyridine nitrogen atoms in NiL(HL)3+, and stacking interaction between the heterocycles in NiL22+.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.