A PYRAZOLATE-BRIDGED CYCLIC TETRANUCLEAR COPPER(II) COMPLEX - SYNTHESIS, CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES

A new pyrazolate-bridged tetranuclear copper(II) complex [{CuL(H2O)}(4 )]. 12H(2)O (H(2)L = 5-methoxycarbonylpyrazole-3-carboxylic acid) was synthesized and its crystal structure determined. The molecule has C-2 symmetry and consists of four copper atoms bridged by four planar L l igands through the nitrogen atoms of the pyrazole groups to form a (-C u-N-N-)(4) 12-membered ring. The co-ordination of each copper is disto rted square planar. The basal plane of each copper atom is nearly para llel to a neighbouring pyrazole plane and perpendicular to another nei ghbouring pyrazole plane. In the crystal there is a hydrogen-bond netw ork between water molecules and carboxylate groups which may control t he packing. The magnetic properties of the complex have also been inve stigated down to 5 K. The fitting of the experimentally data using a H eisenberg Hamiltonian shows that the exchange interaction between the copper atoms propagated through the monopyrazolate bridge is antiferro magnetic with J = -12.34 cm(-1). The reason for this small value relat ive to those in di-mu-pyrazolato-dicopper(II) complexes is discussed.