Kinetics and mechanism of anation of hydroxopentaaquarhodium(III) ion by <img src='http://www.niscair.res.in/jinfo/smaller.gif' border=0><img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-methionine

Abstract

The kinetics of anation of [Rh(OH₂)₅(OH)]²⁺ by <img src='http://www.niscair.res.in/jinfo/smaller.gif' border=0><img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-methionine has been studied spectrophotometrically by monitoring the characteristic absorption peak of the product complex (λ_max = 262 nm) as a function of substrate and ligand concentrations in the 50-65°C temperature range and in the <i>p</i>H range 2.5-4.3. The rate law involving the outersphere complex formation has been established at <i>p</i>H 4.3 as <img src='http://www.niscair.res.in/jinfo/equation39.gif' border=0>. The activation parameters have been calculated and compared with those for water exchange reaction and other substitution reactions. A mechanism· involving the prior formation of an outersphere complex followed by associative interchange (I_a) is suggested where both bond making and bond breaking are equally important in the transition state.