NEW ANTIFERROMAGNETIC DINUCLEAR COMPLEXES OF NICKEL(II) WITH 2 AZIDES AS BRIDGING LIGANDS - MAGNETOSTRUCTURAL CORRELATIONS

Three new nickel(II) dinuclear azide-bridged compounds, (mu1,3-N3)2[Ni(en)2]2(PF6)2 (1), (mu1,3-N3)2[Ni(1,3-pn)2]2-[B(C6H5)4]2 (2), and (mu1,3-N3)2[Ni(1,2-pn)]2(PF6)2 (3), have been synthesized and characterized (en = ethylene-diamine; 1,3-pn = 1,3-diaminopropane; 1,2-pn = 1,2-diaminopropane). The crystal structures of 1 and 2 have been solved. Complex 1 crystallizes in the monoclinic system, space group C2/c, with fw = 731.79, a = 15.252(3) angstrom, b = 17.872(3) angstrom, c = 12.102(2) angstrom, beta = 126.76(2)degrees, V = 2643(1) angstrom3, Z = 4, R = 0.053, and R(w) = 0.057. Complex 2 crystallizes in the monoclinic system, space group p2(1)/n, with fw = 1136.4, a = 9.997(2) angstrom, b = 20.838(3) angstrom, c = 14.269(3) angstrom, beta = 96.76(2)degrees, V = 2952(2) angstrom3, Z = 2, R = 0.052, and R(w) = 0.052. In both complexes the nickel atom is placed in a distorted octahedral environment. The magnetic properties of these compounds have been studied by means of susceptibility measurements vs temperature. The chi(M) vs T plots for 1-3 show the typical shapes for antiferromagnetically coupled nickel(II) dinuclear complexes. By using the spin Hamiltonian -JS1S2, J values for 1-3 were calculated to be -4.6, -114.5, and -77.2 cm-1, respectively. Extended Huckel calculations on the two structurally characterized complexes, compared with two other analogous complexes previously reported in the literature, indicate that the dihedral angle between the N-Ni-N plane and the plane formed by the two N3- bridging ligands is the main factor which dominates the magnetic coupling: the smaller the dihedral angle, the stronger the antiferromagnetic coupling.