Magnetism and structure of a novel trinuclear cluster compound of divalent copper

Abstract

The magnetic properties of a series of salts of the type [Cu₃L₃OH]²⁺ (where HL is pyridine-2-aldehyde oxime and L is the deprotonated ligand) have been examined. All of the compounds showed a magnetic moment of 1.00 B.M. per copper atom over a wide temperature range which suggests that the cation contains a trinuclear cluster of interacting copper atoms. The crystal structure of Cu₃L₃OH(SO₄),xH₂O has been determined by single- crystal X-ray diffraction techniques and confirms that the complex does indeed contain an unusual type of trinuclear cluster of metal atoms. The three copper atoms form an equilateral triangle and the sulphato group exhibits a highly novel ?tripod? bridging function to the Cu₃ triangle. On the other side of the triangle, the hydroxyl group also bridges to all the metal atoms. A qualitative molecular orbital analysis not only suggests that the hydroxyl group is involved in four-centre bonding with the Cu₃ triads, but also highlights its role in reducing the spin of the trimer so that only a doublet ground state is populated between 80-300°K. However, the alternative super-exchange mechanism cannot be ruled out by the magnetic and structural data.