Anation of cis- and trans-[Co(en)(2)(OH2)OH](2+) by C2O42- in the pH range
6-9 occurs via the ion pairs cis- and trans-[Co(en)(2)(OH2)OH](2+).C2O42-,
and both cis- and trans- ion pairs lead to both cis-and trans[Co(en)(2)(OC2
O3)OH2](+) Competing isomerization of the reactants occurs both in the free
ions and in the ion-pairs.