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, 1,2bis(diphenylphosphino)ethane, triphenylphosphite, diisopropyl sulfide, cyclooctadiene and cyclohexylisocyanide) and had the general formula LnCu(µ2-C2O4)CuLn (n = 1 or 2). The Cu I /Cu II mixed-valence trinuclear compound (iPr2S)2Cu I (C2O4)Cu II (C2O4)Cu I (iPr2S)2 was formed concomitantly with the target dinuclear Cu2C2O4(iPr2S)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 3 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.

In the title compound, [Cu(CH 3 CN) 4 ](C 2 HO 4)Á0.5C 2 H 2 O 4 Á-0.5CH 3 CN, the Cu I ion is coordinated by the N atoms of four acetonitrile ligands in a slightly distorted tetrahedral environment. The oxalic acid molecule lies across an inversion center. The acetonitrile solvent molecule is disordered across an inversion center and was refined with half occupancy. In the crystal, the hydrogen oxalate anions and oxalic acid molecules are linked via O-HÁ Á ÁO hydrogen bonds, forming chains along [010]. Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LH5649). metal-organic compounds m544 Royappa et al.