EPR and 1H ENDOR study of the solution equilibria of bis(2-ethyl-2-hydroxy-butanoato(2-))oxochromate(V) and bis(2-hydroxy-2-methylbutanoato(2-))oxochromate(V).

The behavior of the bischelated oxochromium(V) complex of 2-ethyl-2-hydroxybutanoate(2-) and its 2-hydroxy- 2-methylbutanoate(2-) analogue has been reexamined by EPR and 'H ENDOR spectroscopy in a range of solvents. It has been confirmed that the complexes rearrange in solution to yield two species which are in equilibrium, the kinetics of the process being dependent on the nature of the solvent. The results rule out that such a rearrangement is due to an acid-base process involving the alcoholic group of one of the ligands and suggest that the two species are the cis and trans isomeric forms of the bischelated complex, both exhibiting a distorted five-coordinate geometry.