Cyanide-Bridged Fe-Co Polynuclear Clusters Based on Four-Coordinate Cobalt(II)

Treatment of CoCl2·6H2O and tris(pyrazolyl-1-yl)borate tricyanoiron(III) anions at 55 °C afforded a series of new Fe-Co polynuclear clusters: {Co2Cl2(DMF)4[(Tp4-Me)Fe(CN)3]2} (1; Tp4-Me = hydridotris(4-methylpyrazol-1-yl)borate), (H3O+)@{Co4Cl4[(Tp4-Me)Fe(CN)3]4} (2), (MePh3P)4{Co6Cl6[(Tp4-Me)Fe(CN)3]6}·15CH3CN·3CH3OH·2H2O (3), and (BnEt3N)4{Co5Cl8[(Tp∗)Fe(CN)3]4}·4CH3CN·2H2O (4; Tp∗= hydridotris(3,5-dimethylpyrazol-1-yl)borate). They feature an asymmetric [Fe2Co2(CN)4] square, a pseudocubic [Fe4 Co4(CN)12] cluster, a distorted-hexagonal-prism-shaped [Fe6Co6(CN)18] cage, and a bis(trigonal-bipyramidal) cluster of [Fe4Co5(CN)12] fused at one cobalt center, respectively. The Co(II) ions adopt a four-coordinate tetrahedral geometry except for half of 1 in an octahedral geometry. It should be mentioned that 3 and 4 provide two novel molecular skeletons in the cyanometalate family. Interestingly, 1 behaved as a single-molecule magnet with an effective energy barrier for spin reverse of 30.7 K at zero dc field. Our result demonstrated a possible self-assembly route toward high-nuclearity cyanide-bridged clusters by introducing four-coordinate cobalt(II) ions.