Pentanuclear Cyanide-Bridged Complexes Based on Highly Anisotropic CoII Seven-Coordinate Building Blocks: Synthesis, Structure, and Magnetic Behavior

Pentagonal-bipyramidal complexes [Co(DABPH)X(H2O)]X [X = NO3 (1), Br (2), I (3)] were synthesized, and their magnetic behavior was investigated. Simulation of the magnetization versus temperature data revealed the complexes to be highly anisotropic (D approximate to +30 cm(-1)) and the magnitude of the anisotropy to be independent of the nature of the axial ligands. The reaction of 1 with K-3[M(CN)(6)] (M = Cr, Fe) produces the pentametallic clusters [{Co(DABPH)}(3){M(CN)(6)}(2)(H2O)(2)] [M = Cr (4), Fe (5)]. Both clusters consist of three {Co(DABPH)} moieties separated by two {M(CN)(6)} fragments. In 4, the central and terminal Con ions are bound to cyanide groups cis to one another on the bridging {Cr(CN)(6)}, whereas in 5, the connections are via trans cyanide ligands, resulting in the zigzag and linear structures observed, respectively. Magnetic investigation revealed ferromagnetic intramolecular interactions; however, the ground states were poorly isolated because of the large positive local anisotropies of the Co-parallel to ions. The effects of the local anisotropies appeared to dominate the behavior in 5, where the magnetic axes of the Co-parallel to ions were approximately colinear, compared to 4, where they were closer to orthogonal.