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)₂·6H₂O (M = Co or Ni) in a mixture of acetonitrile and methanol afford, upon crystallization via THF vapor diffusion, [Tp₈(H₂O)₁₂Co₆Fe₈(CN)₂₄](ClO₄)₄·12THF·7H₂O (1) and [Tp₈(H₂O)₁₂Ni₆Fe₈(CN)₂₄](ClO₄)₄·12THF·7H₂O (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.