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

Abstract A series of dinuclear copper(I) oxalate complexes was synthesized by the direct acid-base reaction of Cu 2 O 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 L n Cu(μ 2 -C 2 O 4 )CuL n ( n  = 1 or 2). The Cu I /Cu II mixed-valence trinuclear compound (iPr 2 S) 2 Cu I (C 2 O 4 )Cu II (C 2 O 4 )Cu I (iPr 2 S) 2 was formed concomitantly with the target dinuclear Cu 2 C 2 O 4 (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 Cu 2 C 2 O 4 (nbd) was formed. Also, the same reaction with L = 2,9-dimethyl-1,10-phenanthroline or pyridine resulted in the known tetrahedral complex ions [CuL m ] + ( 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.