A PYRAZOLE LIGAND YIELDING BOTH CHLORO-BRIDGED DINUCLEAR AND TETRANUCLEAR COPPER(II) COMPOUNDS - THE CRYSTAL AND MOLECULAR-STRUCTURE OF BIS[MU-CHLORO-CHLORO(3,4-DIMETHYL-5-PHENYLPYRAZOLE)(4,5-DIMETHYL-3-PHENYLPYRAZOLE)COPPER(II)] AND OF (MU-4-OXO)HEXAKIS(MU-CHLORO)TETRAKIS(3,4-DIMETHYL-5-PHENYLPYRAZOLE)TETRACOPPER(II)

The reaction of CuCl2.2H2O and 3(5),4-dimethyl-5(3)-phenylpyrazole (hereafter Hdmppz) gives green crystals that analyze as CuCl2(C11H12N2)2 (1). The green filtrate produces brown crystals of composition Cu4OCl6(C11H12N2)4 (2). The crystal structure of both compounds was determined from single-crystal X-ray data. Crystals of bis[mu-chloro-chloro-chloro-(3,4-dimethyl-5-phenylpyrazole)-(4,5-dimethyl-3-phenylpyrazole)copper(II)] (1) are triclinic, space group P1; a = 9.071(1), b = 11.008(1), c = 11.358(1) angstrom, alpha = 93.42(1), beta = 97.50(1), gamma = 96.16(1)-degrees, Z = 1. The dinuclear unit is located on a crystallographic inversion center. The copper ion is five-coordinated by two pyrazole nitrogen atoms and one bridiging and one non-bridging chloride anion. The coordination is best described as a distorted square pyramid with the long bridging chloride as the top. Surprisingly the two pyrazole ligands are coordinating through different nitrogen atoms, one through the nitrogen atom close to the phenyl substituent and the other through the nitrogen close to the methyl substituent. Crystals of (mu-4-oxo)hexakis(mu-chloro)tetrakis(4,5-dimethyl-3-phenyl-pyrazole)tetra-copper(II) (2) are monoclinic, space group I2/a; a = 20.836(1), b = 11.161(1), c = 22.996(1) angstrom, beta = 104.54(1)-degrees, Z = 4. The copper ions are coordinated by five ligands in a trigonal-bipyramidal arrangement. The pyrazole nitrogen and the oxo-anion form the two tops of the bipyramid and the chlorides form the basal plane. Magnetic susceptibility measurements of 1 and 2 show that there is considerable antiferromagnetic interaction in these compounds as can be expected. For 1 the experimental data could be fitted to a model for a dinuclear compound with 2J as the singlet triplet splitting and zJ' the inter-dinuclear exchange. The best fit was found for g = 2.13, J/k = -5.8 K and zJ'/k = -0.22 K. For 2 a model was used with two different exchange parameters J(a) and J(b). The best fit was obtained for g = 2.11 and J(a)/k = -51 K and J(b)/k = -33 K.