As shown in a previous paper(1), the ethyl α-ketocyclopentylcarboxylate (hereafter HCBCP, according to its non-systematic name carbetoxycyclopentanone) easily undergoes a keto-enolic tautomerism, the enolic, de-protonized species thus forming coordination compounds with Mn(II), Fe(III), Co(II), Ni(II), and Cu(II). In addition to this bidentate ligand, the complexes usually contain coordinated water molecules, thus completing a distorted octahedral coordination around the metallic site. The immediate environment of the metal in these complexes is very similar to that existing in their acetylacetonate compounds, M(acac)n(n=2 or 3). Theseacacderivatives