Pentanuclear cyanide-bridged complexes based on highly anisotropic Co II seven-coordinate building blocks: Synthesis, structure, and magnetic behavior

Pentagonal-bipyramidal complexes [Co(DABPH)X(H2O)]X [X = NO 3 (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 ≈ +30 cm-1) and the magnitude of the anisotropy to be independent of the nature of the axial ligands. The reaction of 1 with K3[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 CoII 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 CoII ions. The effects of the local anisotropies appeared to dominate the behavior in 5, where the magnetic axes of the Co II ions were approximately colinear, compared to 4, where they were closer to orthogonal. © 2011 American Chemical Society.