DINUCLEAR COPPER(II) COMPLEXES CONTAINING NITROSO-OXIMATO BRIDGES - 2DIFFERENT COPPER(II)-BRIDGING ENTITIES FROM THE SAME PRECURSOR

The complexes [Cu(mu-L)Cu(bipy)(EtOH)](ClO4)(2) 2a and [Cu(mu-(1)L)Cu( bipy)(H2O)](ClO4)(2) . H2O 2b [where H(2)L = pyrimidine-2,4-(1H,3H)-di on-6-yl)propylenediamine; H(2)(1)L arises from H(2)L by elimination of a CO molecule from one of the pyrimidine rings] have been obtained fr om the reaction of the precursor [Cu(mu-HL)Cu(H2O)(2)(CH3CH2OH)](ClO4) (3) 1 with bipy and Cu(ClO4)(2) . 6H(2)O, respectively. The structures of 2a and 2b have been solved by X-ray crystallographic methods. The structure of 2a is made up of [Cu(mu-L)Cu(bipy)(EtOH)](2+) cations and two semi coordinated perchlorate anions. The [Cu(1)L] fragment coordi nates to the external Cu(2) ion through the two deprotonated oximate o xygens to afford a dinuclear structure with double syn-syn mitroso-oxi mate bridge and an intramolecular Cu-Cu distance of 3.731(1) Angstrom. The Cu(1) exhibits a CuN4O2 pseudoctahedral coordination polyhedron w hereas the geometry around the Cu(2) ion is distorted square-pyramidal CuN2O2O. The structure of 2b consists of [Cu(mu-(1)L)Cu(bipy)(H2O)](2 +) cations, two perchlorate anions and one lattice water molecule. The coordination of the [Cu((1)L)] unit to the external Cu(2) ion takes p lace through the two nitroso-oximate groups, one of them disordered on two sets of crystallographic positions, one with a 63% occupancy and the other with a 37% occupancy. The intramolecular Cu(1)-Cu(2) distanc e is 3.655(3) Angstrom. The Cu(1) occupying the inner site of the (1)L (2-) ligand exhibits a 4+1 CuN4O (63%) [CuN3O2 (37%)] coordination env ironment whereas the Cu(2) atom is in a distorted square-pyramidal CuN 2O3 (63%) [CuN3O2 (37%)] environment. The dinuclear fragments of 2a an d 2b are almost planar with dihedral angles between the mean basal coo rdination planes of 4.1(2)degrees and 4.6 degrees, respectively. Both 2a and 2b are diamagnetic at room temperature, so that J < -1000 cm(-1 ). The structural and magnetic data for these complexes have been comp ared with those of similar compounds, but no correlation between the m agnitude of the exchange interaction and the degree of deviation from planarity is evident. In view of this and to rationalize the influence of the distortion from planarity on the magnetic properties in oximat e-bridged complexes, MO Extended Huckel calculations have been perform ed. Copyright (C) 1996 Elsevier Science Ltd