OXIMATO COMPLEXES .2. DINUCLEAR DIMETHYLGLYOXIMATO COMPLEXES OF COPPER(II) WITH A NEW COORDINATION MODE OF THE OXIMATE LIGAND

Three new dinuclear copper(II) complexes of formula [Cu2(dmg)(Hdmg)(H2dmg)]Cl.H2O 1, [Cu2(dmg)(Hdmg)(H2dmg)]ClO4 2 and [{Cu2(dmg)(Hdmg)(H2dmg)}2(SO4)].2.5H2O 3 (H2dmg = dimethylglyoxime) have been synthesised. The crystal structure of 3 was solved by single-crystal X-ray diffraction methods: monoclinic, space group C2/c, a = 22.736(2), b = 21.367(l 2), c = 11.781 (7) angstrom, beta = 122.97(5)degrees and Z = 4. The structure consists of two cationic binuclear [Cu2(dmg)(Hdmg)(H2dmg)]+ units bridged by a sulfate anion, leading to a neutral tetrameric entity, and lattice water. In the dinuclear cation the copper(II) ions are bridged by two oximate groups, one through the nitrogen and oxygen atoms and the other only through the oxygen atom. The intramolecular Cu(1) ... Cu(2) distance is 3.266(2) angstrom. The geometry around the copper atoms is a distorted square pyramid: the basal plane for Cu(1) comprises three nitrogen and one oxygen atom of the Hdmg- and dmg2- groups, whereas that of Cu(2) is formed by two nitrogens of H-2dmg and two oximate oxygens; two oxygen atoms from a sulfate ion occupy the apical position of each copper atom. The temperature dependence of the molar magnetic susceptibility (100-300 K) for 1-3 reveals a very strong intramolecular antiferromagnetic coupling between copper(II) ions (J ca.-950 cm-1).