Assembling Five-Coordinated Cobalt(II) Dimers in a Cyanide Framework with nia Topology and Slow Magnetic Relaxation

The microwave-assisted reaction of a simple cobalt salt and diamagnetic hexacyanidocobaltate(III) produces an unprecedented cyanide-bridged 3D framework featuring pentacoordinate binuclear Co(II) secondary building units. Structural analysis shows that the Co2+ ions, in a distorted trigonal bipyramidal geometry, are bridged by two O2–/O atoms and connected by CoIII(CN)63– anions, forming a unique nia topology. DC magnetic susceptibility and theoretical calculations indicate strong ferromagnetic interactions between the Co2+ ions, resulting in an S = 3 ground state with significant easy-axis magnetic anisotropy. The ac magnetic susceptibility indicates the compound exhibits field-induced slow magnetic relaxation happening through Raman and direct magnetic relaxation, establishing the compound as the first cyanide-bridged Co(II) single-molecule magnet (SMM) framework with a nia topology.