KINETICS AND MECHANISM OF ANATION OF HYDROXOPENTAAQUARHODIUM(III) IONBY DL-METHIONINE

The kinetics of anation of [Rh(OH2)(5)(OH)](2+) by DL-methionine has b een studied spectrophotometrically by monitoring the characteristic ab sorption peak of the product complex (lambda(max) = 262 nm) as a funct ion of substrate and ligand concentrations in the 50-65 degrees C temp erature range and in the pH range 2.5-4.3. The rate law involving the outersphere complex formation has been established at pH 4.3 as d[Rh(O H2)(2)(OH)(L)(+)]/dt = k(a)K(E)[Rh(OH2)(5)(OH)(2+)](T)[LH]/1 + K-E[LH] The activation parameters have been calculated and compared with thos e for water exchange reaction and other substitution reactions. A mech anism 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.