Crystal Structures and Magnetic Properties of Two Octacyanotungstate(IV) and (V)-Cobalt(II) Three-Dimensional Bimetallic Frameworks^§

The synthesis, X-ray structures, and magnetic behavior of two new, three-dimensional compounds [WIV{(μ-CN)4CoII(H2O)2}2·4H2O]n (1) and [{WV(CN)2}2{(μ-CN)4CoII(H2O)2}3·4H2O]n (2) are presented. Compound 1 crystallizes in the tetragonal system, space group I4/m with cell constants a = b = 11.710(3) Å, c = 13.003(2) Å, and Z = 4, whereas 2 crystallizes in the orthorhombic system, space group Cmca with cell constants a = 13.543(5) Å, b = 16.054(6) Å, c = 15.6301(9) Å, and Z = 4. The structure of 1 shows alternating eight-coordinated W(IV) and six-coordinated Co(II) ions bridged by single cyanides in a three-dimensional network. The geometry of each [WIV(CN)8]4- entity in 1 is close to a square antiprism. Its eight cyanide groups are coordinated to Co(II) ions which have two coordinated water molecules in trans position. The structure of 2 consists of alternating eight-coordinated W(V) and six-coordinated Co(II) ions linked by single cyanide bridges in a three-dimensional network. Each [WV(CN)8]3- unit shows a geometry close to a square antiprism. Only six of its eight cyanide groups are coordinated to Co(II) ions while the other two are terminal. The Co(II) ion in 2 has the same CoN4O2 environment as in 1. The magnetic behavior of 1 is that of magnetically isolated high spin Co(II) ions (SCo = 3/2), bridged by the diamagnetic [WIV(CN)8]3- units (SW(IV) = 0). The magnetic behavior of 2, where the high spin Co(II) ions are bridged by the paramagnetic [WV(CN)8]3- units [SW(V) = 1/2], is that of ferromagnetically coupled Co(II) and W(V) giving rise to an ordered ferromagnetic phase below 18 K. The magnetic properties of 1 are used as a blank to extract the parameters that are useful to analyze the magnetic data of compound 2.