, a = 7.4037(13) Angstrom, b = 10.709(3) Angstrom, c = 10.9569(19) Angstrom, alpha = 110.742(16)degrees, beta = 95.600(19)degrees, gamma = 100.195(19)degrees, V = 787.4(3) Angstrom(3), Z = 2, R/R(w) = 0.036/0.026. The oxygen atom of the 2-carboxylate group and the oxo ligand are situated in apical positions of a pseudotrigonal plane formed by the nitrogen atom and the centres of the two peroxo groups. The compounds rapidly oxidize sodium tris(3-sulfonatophenyl)phosphine, in water, to the corresponding oxide. The results are discussed with reference to the reported insulin mimetic activity of this class of compounds.