Synthesis, structure, and magnetic properties of the low-symmetry tetranuclear cubane-like nickel complex [Ni-4(pypentO)(pym)(mu(3)-OH)(2)(mu-Oac)(2)(NCS)(2)(OH2)]

The terranuclear [Ni-4(pypentO)(pym)(mu (3)-OH)(2)(mu -Oac)2(NCS)(2)(OH)(2) ] cubane-like complex has been prepared, and its structure and magnetic pro perties have been studied (pypentO and pym are the deprotonated forms of 1, 5-bis[(2-pyridylmethyl)amino]pentane-3-ol and 2-pyridylmethyl, respectively ). The X-ray diffraction analysis of this novel nickel complex (C61H74N14O2 5.5S4Ni8, monoclinic, P2(1), a = 13.9375(14) Angstrom, b = 20.6604(18) Angs trom, c = 16,6684(19) Angstrom, beta = 110.619(12)degrees, Z = 2) showed a Ni4O4 cubane arrangement of four nickel atoms, four mu (3)-O bridging ligan ds (one pypentO, one pym, and two OH-), two syn(-)syn bridging acetates, an d three terminal monodentate ligands (two NCS- and one OH2). In this low-sy mmetry elongated cubane, the four Ni-Ni long distances (3.18 Angstrom) corr espond to the faces of the cube:including two mu (3)-OR bridges, and the tw o Ni-Ni short distances (2.94 Angstrom) correspond to the faces including t wo mu (3)-OR and one acetate bridges. The temperature dependence of the mag netic susceptibility was fitted with J(q) = -3.09 cm(-1), J(2) = 15.0 cm(-1 ), J(3) = 6.72 cm(-1), and g = 2.27. The differences in sign among the J(1) , J(2), and J(3) superexchange interactions is in good agreement with the d ifferent types of faces present in this Ni4O4 cubane core. The two faces of the cube, including two mu (3)-OR bridges associated with one acetate brid ge, exhibit ferromagnetic interactions, while the four faces which include only mu (3)-OR bridges exhibit antiferromagnetic interactions, The very sma ll zero field splitting may be attributed to the fact that the ground slate is diamagnetic. The nature of the ground State is confirmed by the good si mulation of the magnetization curves at 2 and 5 K (diagonalization of the f ull matrix taking into account all energy levels obtained with the paramete r set resulting from the fit of the susceptibility curve). The large differ ences in J values resulting from small differences in Ni-O-Ni angles in thi s Ni4O4 core of very low symmetry reflect a quite strong magnetostructural correlation.