Kinetics of the equilibrium: cis-⇌trans-diaquobis(oxalato)chromate(III)

Abstract

An equilibrium between the cis- and the trans-forms of diaquobis(oxalato)chromate(III) anions is established in aqueous solution at pH 3–4. The equilibrium constant, 0·17 ± 0·01, is insensitive to temperature changes in the range 283–303 K. The enthalpy and the entropy of activation are 67·6 ± 2·7 kJ mol^–1 and –48·5 ± 4·6 J mol^–1 K^–1 for the forward reaction and 67·6 ± 2·7 kJ mol^–1 and –41·0 ± 4·6 J mol^–1 K^–1 for the backward reaction respectively. These parameters and the rate constants are unchanged, within experimental error, in solutions in heavy water. A mechanism involving a trigonal-bipyramidal intermediate, containing a nonchelating oxalate, has been proposed.