Volume 220, Issue 8

The complexation of a newly synthesized mercapto compound, (2-mercapto-4-methyl phenyl)-2-benzamido-3-ethoxy thiopropenate, with Co 2+ , Cu 2+ , and Hg 2+ have been studied in binary dimethylsulphoxide–acetonitrile (DMSO-AN) mixtures at different temperatures by a conductometric technique. Stoichiometry and stability of the resulting complexes were evaluated by KINFIT program and from molar conductivity–mol ratio (ligand to metal) data were found to vary in the sequence Co 2+ > Cu 2+ > Hg 2+ . In all cases, evidence for the formation of both 1:1 and 2:1 (ligand to metal) complexes were obtained. The stability of these complexes increases with decreasing temperature. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. In all cases, the complexes were found to be enthalpy and entropy stabilized. Furthermore, in all of the complexes which were studied, not only an increase in the percentage of dimethylsulfoxide in DMSO-AN solvents mixtures would drastically decrease the stability of the resulting complexes, but also enthalpy and entropy would be more positive and negative respectively (decrease of stability).

Low frequency vibrations in [Ni(H 2 O) 6 ](ClO 4 ) 2 and [Ni(D 2 O) 6 ](ClO 4 ) 2 were measured by the FIR Fourier Transform Spectroscopy method. They were compared with those obtained by the IINS method. No evidence of proton glass discovered by the IINS was observed via the FIR method. By applying the band contour method, the barrier to rotation U act for H 2 O groups in [Ni(H 2 O) 6 ](ClO 4 ) 2 crystals was determined. A III–II phase transition mechanism was proposed.

Rate coefficients and branching ratios for unimolecular reactions of alkoxyl radicals in the temperature range 200 to 1500 K and in the pressure range 10 −2 to 10 4 bar are presented. Special emphasis is given to the change of the relative importance of different reaction channels. This is evident for longer chain alkoxyl radicals which at lower temperatures undergo isomerisation via an energetically favourable six-member ring transition state. At temperatures above >600 K, however, the rates of the alternative decomposition pathways become faster than that of isomerisation. The theoretical approach to derive unimolecular rate coefficients makes use of extensive (G2/G3) ab initio calculations. These are used as input data for RRKM calculations to which a tunnelling probability of the generalised Eckart type has been included on the microcanonical level. A subsequent multi-channel master equation (ME) treatment yields thermal rate coefficients and complete fall-off curves for arbitrary pressure and temperature conditions. The kinetics of two linear chain alkoxyl radicals, 1-butoxyl and 2-pentoxyl, have been analysed to show the expected complex temperature and pressure behaviour resulting from the competition of multiple accessible reaction channels, each with its specific p , T -dependence. Additional results are reported for the minimum temperatures where channel switching can occur, the trajectory of these characteristic points on the p , T -surface, and the temperature dependence of the fractional ratios of the unimolecular reaction channels and the bimolecular reaction with oxygen at ambient atmospheric pressure.

Apparent molar adiabatic compressibility, K 2,φ,S , of glycine, DL-α-alanine, DL-α-amino- n -butyric acid, L-leucine and L-phenylalanine in water and in (0.5, 1.0, 2.0, 4.0, 5.5 mol kg −1 ) aqueous sodium acetate and in (0.5, 1.0, 1.5, 2.0 mol kg −1 ) aqueous magnesium acetate solutions has been determined from sound velocity, u , measurements at 298.15 K. The partial molar adiabatic compressibilities at infinite dilution, K 0 2,S , obtained from K 2,φ,S data have been used to calculate the corresponding partial molar adiabatic compressibilities of transfer at infinite dilution, Δ t K 0 2,S , from water to aqueous sodium acetate and magnesium acetate (cosolutes) solutions. The Δ t K 0 2,S values are positive for the studied amino acids in case of both the cosolutes and the values increase with the increase of the concentrations of both the cosolutes. The trends of Δ t K 0 2,S have been rationalized in terms of the hydration of hydrophilic and hydrophobic parts of the amino acids studied. The interaction coefficients and hydration number, n H , have also been calculated and are discussed in terms of the dehydration effect of sodium acetate and magnesium acetate upon the amino acids in solutions. Attempt has been made to correlate these results with the earlier reported volumetric and viscometric studies for the same systems.

A new organic substrate has been used to promote oscillations under batch conditions in the Briggs–Rauscher oscillating system. The new substrate, 1,4-cyclohexanedione (CHD), reacts with aqueous iodine via an enol mechanism. We discuss the effect of the initial concentrations, the temperature and chemical perturbations. In a definite range of concentrations long-lived oscillations with two significantly different frequency periods were observed. The low frequency parts are temperature-dependent while the high frequency oscillations do not show temperature dependence. The inhibitory effects of 1,4-hydroquinone and 1,4-benzoquinone on the oscillations and the kinetics of some important component reactions were studied to develop a model for the simulation of the observed oscillations.

Both electrochemical (at Pt electrode) and homogeneous (with Cl 2 (aq)) oxidation of the aqueous solution of Ni(II)-N 3 − yields the solution of a brown product that was found to be the azide complex of Ni(IV). Its UV/Vis spectrum, consisting of a single band of high intensity (ε = 26500 cm −1 dm 3 mol −1 at λ max = 471 nm), has been ascribed to the ligand-to-metal charge-transfer mechanism (LMCT). The Ni(IV)-N 3 − complex undergoes spontaneous decomposition in aqueous solution, with Ni(IV) reduced back to Ni(II) and N 3 − oxidized to molecular nitrogen. The first-order kinetics of this process was studied spectrophotometrically and the following parameters were found: rate constant k = 1.96×10 −2 s −1 , Arrhenius activation energy E a = 82±7 kJ mol −1 , standard activation enthalpy Δ H ≠0 = 79±7 kJ mol −1 , and small standard activation entropy Δ S ≠0 = 10±20 J mol −1 K −1 . The outline mechanism for the intramolecular redox Ni(IV)-N 3 − decomposition has been suggested. Nickel ions at various oxidation states were found to be powerful catalysts for the redox processes of azide ions.