Synthesis, crystal structure and magnetic properties of [Cu(bipy)2(CH3COO)][Cu(bipy)2(Cr(C2O4)3)]·∼10.5H2O, the first compound containing the [Cr(C2O4)3]3− building block acting as a monodentate ligand

The reaction between copper(II) acetate with 2,2′-bipyridine and K3[Cr(C2O4)3] leads to the novel salt [Cu(bipy)2(CH3COO)][Cu(bipy)2(Cr(C2O4)3)]·∼10.5H2O, 1 (bipy=2,2′-bipyridine). The crystal structure of 1 consists of mononuclear cationic species [Cu(bipy)2(CH3COO)]+ and heterobinuclear anionic units, [Cu(bipy)2(Cr(C2O4)3)]−. The tris-oxalato-chromium entity behaves as a monodentate ligand toward the copper(II) ion within the complex anion. The distance between Cr(III) and Cu(II) across the bridging oxalato group is 5.056(2) A. The copper(II) ions exhibit a distorted trigonal bipyramidal surrounding in both cationic and anionic species. The π–π stacking interaction between bipy ligands of the neighboring [Cu(bipy)2(CH3COO)]+ mononuclear entities leads to chains of copper atoms running along the b axis. Magnetic susceptibility measurements of 1 in the temperature range of 1.9–290 K reveal a quasi-Curie law behavior, the magnetic coupling between Cr(III) and Cu(II) through the bridging oxalato group with the bidentate/monodentate coordination mode being negligible.