Synthesis, characterization, structures and magnetic property of chiral oxalate-bridged dicopper(II) complexes

The oxalato-bridged dicopper(II) complexes [Cu-2(mu-ox)(L-RR)(2)(H2O)(2)(ClO4)(2)] (1), [Cu-2(mu-ox)(L-RR)(2)(CH3COCH3)(2)(ClO4)(2)](1a), [Cu-2(mu-ox)(L-SS)(2)(H2O)(2)(ClO4) 2] (2) and [Cu-2(mu-ox)(L-RR)(L-SS)(2)(CH3COCH3)(2)(ClO4)(2)] (3) [L-RR = (8R, 10R)-(-)-[4,5]-pineno-2,2'- bipyridine, L-SS=(8S, 10S)-(+)-[4,5]-pineno-2,2'-bipyridine; ox(2-) = oxalate] were first prepared. A possible mechanism for the formation of the chial dicopper(II) complexes was proposed. Based on elemental analysis, conductance measurement, UV-Vis spectra, CD spectra and X-ray single-crystal diffraction, the oxalato-bridged structures of 1 and 2 were deduced to adopt two Cu(II) ions and the bridged oxalate lying in the nearly same plane. The crystal structures of 1a and 3 reveal that the coordination geometry around each Cu(II) ion is an elongated and distorted octahedron and two axial solvent molecules and two perchlorate ions are anti to each other respectively in both binuclear molecules. The solution CD spectra of 1 and 2 in the visible d-d range show very weak Cotton effects with peaks at 588 and 779 nm, which are approximately of mirror image, suggesting the optical activities may be derived from the vicinal effects of the chiragenic centers at the pinene group of L-RR and L-SS, respectively. Complex 1 has been characterized by variable-temperature magnetic susceptibility and the data was least-square fitted to the Blenaey-Bowers equation. The exchange integral J was found to be. 338.41(4) cm(-1), indicating a strong antiferromagnetic interaction between two copper(II) ions.National Natural Science Foundation of China [20773098, 20973136]; Innovation Foundation of Xiamen University [XDKJCX20061027