2 NEW ONE-DIMENSIONAL ANTIFERROMAGNETIC NICKEL(II) COMPLEXES BRIDGED BY AZIDO LIGANDS IN CIS POSITIONS - EFFECT OF THE COUNTERANION ON THE MAGNETIC-PROPERTIES

Two new nickel(II) polynuclear end-to-end azide bridged compounds were synthesized and characterized: [NiL(2)(mu-N-3)](n)(ClO4)(n) (1) and [NiL(2)(mu-N-3)](n)(PF6)(n) (2); L = 1,2-diamino-2-methylpropane. The crystal structures of 1 and 2 were solved. Complex 1 crystallizes in the orthorhombic system, space group P2(1)2(1)2(1), With fw = 376.49, a = 7.392(2) Angstrom, b = 13.879(3) Angstrom, c = 16.178(3) Angstrom, V = 1660(1) Angstrom(3), Z = 4, R = 0.049, and R(W) = 0.052. Complex 2 crystallizes in the orthorhombic system, space group Pbn2(1), with fw = 422.00, a = 17.022(3) Angstrom, b = 13.760(2) Angstrom, c = 7.550(1) Angstrom, V = 1768.4(8) Angstrom(3), Z = 4, R = 0.057, and R(W) = 0.060. In the two complexes, the nickel atom is situated in similar distorted octahedral environments. The Ni-Ni distances are 5.313 Angstrom for 1 and 5.335 Angstrom for 2. The two complexes are similar and may be described as helicoidal chains. The only marked difference is that the ClO4- chain is more compact. The magnetic properties of the two compounds were studied by susceptibility measurements vs temperature. The chi(M) vs T plot for 1 shows the typical shape for one antiferromagnetically coupled nickel(II) one-dimensional complex with a maximum near 30 K. In contrast, the absence of a maximum down to 4 K in the chi(M) vs T plot for 2 indicates low antiferromagnetic coupling. From the spin Hamiltonian -J Sigma SiSj, J values for 1 and 2, were -16.8 and -3.2 cm(-1), respectively. This difference in magnetic behavior may be explained in terms of the distortion of each Ni(II) ion, the compactness of the chains, and the possibly different magnetic pathways from a molecular orbital point of view.