Copper(I) oxalate complexes: Synthesis, structures and surprises

A series of dinuclear copper(I) oxalate complexes was synthesized by the direct acid-base reaction of Cu2O with oxalic acid in ethanol with a ligand, or in neat ligand. The complexes incorporated a variety of ligands L(L = triphenylphosphine, 1,2-bis(diphenylphosphino)ethane, triphenylphosphite, diisopropyl sulfide, cyclooctadiene and cyclohexylisocyanide) and had the general formula LnCu(mu(2)-C2O4)CuLn (n =1 or 2). The Cu-I/Cu-II mixed-valence trinuclear compound (iPr(2)S)(2)Cu-I(C2O4)Cu-II(C2O4)Cu-I(iPr(2)S)(2) was formed concomitantly with the target dinuclear Cu2C2O4(iPr(2)S)(4) complex, shedding light on the mechanism of disproportionation of this family of complexes. With norbornadiene (nbd) as a ligand, however, a coordination polymer Cu2C2O4(nbd) was formed. Also, the same reaction with L = 2,9-dimethyl-1,10-phenanthroline or pyridine resulted in the known tetrahedral complex ions [CuLm](+) (m = 2 or 4). Lastly, the ligand di-2-(1-di-(2-picolyl)amino)propyl disulfide produced not the expected Cu(I) oxalate complex, but a Cu(II) picolylamine oxalate coordination polymer. All products were structurally characterized by single-crystal X-ray diffraction if soluble, and by powder X-ray diffraction methods if not. (C) 2016 Elsevier Ltd. All rights reserved.