Ján Benko

Molecular, supramolecular and solution structures of peroxovanadium complexes with ON and O3N donor set ligands: two new types of cationic–anionic peroxovanadium(V) peroxovanadates(V)

The complexes, [VO(O(2))(pa)(2)]ClO(4).3H(2)O (1), [VO(O(2))(pa)(2)][VO(O(2))(2)(pa)].3H(2)O (2), [VO(O(2))(pa)(2)][VO(O(2))(ada)].2H(2)O (3) and [VO(O(2))(pa)(pca)].H(2)O (4)[pa = picolinamide, ada = carbamoylmethyliminodiacetate(2-) and pca = 2-pyrazinecarboxylate(1-)], were synthesized. 2 and 3 are new types of peroxovanadium complexes: monoperoxovanadium diperoxovanadate (2) and monoperoxovanadium monoperoxovanadate (3). The complexes were characterized by chemical analysis and IR spectroscopy, and 1, 3 and 4 also by X-ray analysis. The structure of 1 is disordered, with alternating positions of the oxo and peroxo ligands. The peroxo oxygen atoms, O(p), in 1 are involved in weak hydrogen bonds with water molecules and close intramolecular C-HO...(p) bonds [d(HO(p)) approximately 2.0 A]. The supramolecular structure of 1 is formed by a network of hydrogen bonds and strong attractive intermolecular pi-pi interactions between the pyridine rings. The supramolecular architecture in 4 is constructed by (N,O)-H...O hydrogen bonds between the neutral complex molecules and water of crystallization. The peroxo oxygen atoms in 4 form intramolecular C-H...O(p) bonds [d(H...O(p))= 2.303 A]. The pa and pca ligands are ON coordinated via the oxygen atoms of the C(NH(2))=O and COO(-) groups, respectively, and nitrogen atoms of the heterocyclic rings, and ada as a tetradentate O(3)N ligand. The thermal analysis of 4 showed that the loss of water of crystallization and the active oxygen release (T(min)/ degrees C 82, T(max)/degrees C 165) are, under given conditions, individual processes separated by the temperature interval 90-132 degrees C. The solution structures and stability were studied by UV-VIS and (51)V NMR spectroscopies.

Solvent effects on the Co(NH3)4(pzCO2)2+–Fe(CN)64– reaction. An interpretation based on spectroscopic data

The reduction of Co(NH3)4(pzCO2)2+(pzCO2= pyrazinecarboxylate) by Fe(CN)64– has been studied in several isodielectric binary aqueous mixtures (water–tert-butyl alcohol, water–ethylene glycol and water–glycerol) at 298.2 K. Spectroscopic data have been obtained for the metal-to-metal charge-transfer band within the ion-pair, Co(NH3)4(pzCO2)2+/Ru(CN)64–. From these data, the Gibbs energies of activation for the thermal electron-transfer reaction have been calculated and compared with those obtained from a kinetic study. The two series of data corresponding to the different water–cosolvent mixtures are of the same order of magnitude but quantitative agreement between calculated and experimental data is not found. This discrepancy is discussed with the main conclusions being: (i) The classical model of the solvent, with a linear response, does not give correct predictions for the Gibbs energy of reorganization: the trend in changes of this magnitude calculated from the model is opposite to that found experimentally. (ii) Differences between the experimental and calculated Gibbs energies of activation arise from (1) the distance effect and (2) a failure of Hushs formulae based on linear response of the medium.

Redox reactions of cobalt(III) complexes in aqueous organic mixtures effects: of single ion assumptions on initial state-transition state solvation analysis

SummarySolvent effects on the kinetics of redox reactions of cobalt(III) complexes were assessed in aqueous mixtures containing methanol,t-butanol, and acetone according to three different extra-thermodynamic assumptions —Wells, TATB, and TPTB** — at 298.2 K. The calculated values of transfer functions of individual ions and initial and transition states were often markedly different. In some cases these differences led to different conclusions in the evaluation of the role of solvation in the reactions investigated.

KINETICS OF SUBSTITUTION OF NICOTINAMIDE AT PENTACYANO(NICOTINAMIDE)IRON(II) BY DIMETHYL SULFOXIDE IN AQUEOUS AND NON-AQUEOUS SOLVENTS

Abstract The effect of organic cosolvent on the rate constant and activation parameters δH‡, δS‡ of substitution of nicotinamide at pentacyano(nicotinamide)iron(II) by dimethyl sulfoxide was investigated in mixtures containing up to 50% methanol, t-butanol, acetone, acetonitrile, glycerine and glycol. From correlations between the logarithm of the rate constant and Grunwald-Winstein Y values, and between δ m δG‡ and excess Gibbs free energy of mixing GE, the effect of the change in the solvation on the reaction rate was elucidated. The effects of pH on the reaction rate and activation parameters, and the effect of organic cosolvent on the shift of the charge-transfer band of the complex mentioned above are also reported.

Effect of acid-base equilibria of reactants and the effect of waterorganic mixtures on the kinetics of oxidation of cysteinsulphenatobis(ethylenediamine)cobalt(III) ion by periodate

SummaryThe kinetics of oxidation of cysteinsulphenatobis(ethylenediamine)cobalt(III) ion by periodate were investigated in mixtures containing up to 40%t-BuOH andi-PrOH. The effect of acid-base equilibria on the rate constants and activation parameters ΔH≠, ΔS≠ and the effect ionic strength on the rate constant at different concentrations HClO4 are also reported. The solvent effects on the oxidation at the different pH are interpreted in terms of solvation of the initial and transition states.

Kinetics of oxidation of pentaammine-isothiocyanato-cobalt(III) ion with peroxodisulphate and periodate in water and water-organic mixtures

SummaryThe kinetics of oxidation of [Co(NH3)5(NCS)]2+ by peroxodisulphate and periodate were investigated at different ionic strengths, and at different temperatures and concentrations of perchloric acid. Rate constants and activation parameters are also reported in mixed water-organic solvents. It was shown that the acid-base equilibria involving S2O8−2, and IO4− ions are important in the reactions studied. Solvent effects on the oxidation are interpreted in terms of the solvation of both the initial state and the activated complex.

Solvent effects on the kinetics of oxidation of cysteinatobis(ethylenediamine)cobalt(III) ion by peroxodisulphate

The kinetics of oxidation of cysteinatobis(ethylenediamine)cobalt(III) ion, [Co(CysOS)(en)2]+, by peroxodisulphate were investigated at different ionic strengths, adjusted with various electrolytes, and at different temperatures and concentrations of perchloric acid. Rate constants and activation parameters are also reported for this oxidation in mixtures containing up to 40% acetone, t-butyl alcohol, isopropyl alcohol, or acetonitrile. The solubilities of [Co(CysOS)(en)2]ClO4 and KClO4 have been determined in water and aqueous acetone and aqueous t-butyl alcohol at 298.2 K. From these values, Gibbs free energies of transfer for [Co(CysOS)(en)2]+ and S2O82– have been estimated. The solvent effects on the oxidation have been divided into their initial-state and transition-state components.

Reactions of carbonyl compounds in basic solutions. Part 35

The kinetics of the alkaline hydrolysis and the configuration, conformation and electronic structure were studied using IR, NMR spectroscopy, X-ray analysis and AM1 theoretical calculations for a series of (Z)-4-(substituted benzylidene)-2-phenyl-4H-oxazol-5-ones (1) and compared with analogous results reported for (E)-4-benzylidene-2-phenyl-4H-furan-5-ones (5) and related compounds.

Study of the reduction of Co(NH3)4(pzCO2)2+ by Fe(CN)54− in binary aquerous mixtures: An interpretations of solvent effects based on spectroscopic data

Abstract The reduction of [Co(NH 3 ) 4 (pzCO 2 )] 2+ (pzCO 2 =pyrazincarboxylato) by [Fe(CN) 6 ] 4- has been studied in several water-methanol mixtures. This study, in addition to the spectroscopic data obtained for the metal-to-metal charge transfer band of the ion-pair [Co(NH 3 ) 4 (pzCO 2 )] 2+ -[Ru(CN) 6 ] 4- and of the binuclear complex [(NH 3 ) 5 CoNCRu(CN) 5 ] - in the same mixtures, supports the idea that the classical (continuun) model of solvent, with a linear response of the polarization, does not give correct predictions for the free energy of solvent reorganization in solvent mixtures.

Solvent Effect on the Kinetics of Oxidation of [Co(en)2SCH2CH2 NH2]2+ by S2O8 2−

The effect of the solvent on rate of the oxidation of [Co(en)2SCH2CH2NH2]2+ by S2O82− in aqueous mixtures of methanol (MeOH), tert-butyl alcohol (ButOH), acetonitrile (AN), ethylene glycol (EG) and ethylene carbonate (EC) has been analysed as regards initial and transition state contributions. From kinetic measurements and solubilities of the reactants, the Gibbs transfer functions, ΔGt°, corresponding to transfer of reactants and activated complex from water to water-organic mixtures were evaluated. The trends of the transfer functions are discussed in terms of ion-solvent interactions and the structural effects in the solvent mixtures.