Syntheses, structures, and magnetic properties of the face-centered cubic clusters [Tp8(H2O)12M6Fe8(CN)24]4+ (M = Co, Ni)

Reactions between K[TpFe(CN)(3)] (Tp(-) = hydrotris(1-pyrazolyl)borate) and M(ClO4)(2)center dot 6H(2)O (M = Co or Ni) in a mixture of acetonitrile and methanol afford, upon crystallization via THF vapor diffusion, [Tp(8)(H2O)(12)Co6Fe8(CN)(24)](ClO4)(4)center dot 12THF center dot 7H(2)O (1) and [Tp(8)(H2O)(12)Ni6Fe8(CN)(24)](ClO4)(4)center dot 12THF center dot 7H(2)O (2). Both compounds contain cyano-bridged clusters with a face-centered cubic geometry, wherein octahedral Co-II or Ni-II centers are situated at the face-centering sites. The results of variable-temperature magnetic susceptibility measurements indicate the presence of ferromagnetic exchange coupling within both molecules to give ground states of S = 7 and 10, respectively. Low-temperature magnetization data reveal significant zero-field splitting, with the best fits for the Co6Fe8 and Ni6Fe8 clusters yielding D = -0.54 and 0.21 cm(-1), respectively; ac magnetic susceptibility measurements performed on both samples showed no evidence of the slow relaxation effects associated with single-molecule magnet behavior.