We report on a convenient synthesis of the ligand precursor, diethylethylene-1,2-bis(oxamate), (Et
2H
2oeo,
1), and show how a partial and preferential hydrolysis of the ester group can give rise to the dianionic ligand, (H
2oeo)
2−. Reaction of this ligand with Cu(II) affords the neutral dimeric species, [Cu
2(H
2oeo)
2], which has a low aqueous solubility. We describe the crystal structure of the hydrate Cu
2(H
2oeo)
2(H
2O)
4 (
2) and report magnetic studies that show a weak exchange interaction in the solid. Under more basic conditions and in the presence
of Cu(II) ions, we are able to avoid amide cleavage and yet deprotonate the amide group, resulting in the formation of the
highly soluble [Cu(Hoeo)
2]
4− complex anion. The structure of (NBu
4)
4[Cu(Hoeo)
2](H
2O)
4 (
3) is described and compared with the recently reported anhydrous phase.