Influence of a Small Amount of Water on the Polarographic Reduction of Nickel(11) Perchlorate in Acetonitrile

Abstract

The stability constants of Ni (CH₅CN), _p (H₂0)p2+ (P=1 to 4) were roughly estimated from the shift of an absorption maximum for nickel(II) measured as a function of water concentration in an acetonitrile solution. The chemical species Ni (CH, CN) (H₂0)52+ was found to be predominant over a mole fraction range of water from 0.4 to O.9 in an acetonitrile-water mixture. When tetraethylammonium perchlorate was used as a supporting electrolyte, a doublestep reduction wave was obtained for nickel ( ) perchlorate in acetonitrile containing a small amount of water. The kinetic character of the first wave was proved from its temperature dependence. The ratio of the first wave height to the total one was increased in proportion to water concentrations less than 40 mmol/kg. It was attempted to interpret the first wave as kinetically controlled by the chemical reaction preceding an electron transfer step:The proposed mechanism could be supported from the linear relationship between the parameter AV t and AR / pk estimated from the polarographic limiting currents and the calculated distribution ratio of the complex species respectively. The double-layer capacity measurements revealed that no appreciable amount of Et, INT+ cation was adsorbed onto a DME surface in an acetonitrile solution.