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 [W-IV{(mu-CN)(4)-Co-II(H2O)(2)}(2).4H(2)O](n) (1) and [{W-V(CN)(2)}(2){(mu-CN)(4)Co-II(H2O)(2)}(3).4H(2)O](n) (2) are presented. Compound 1 crystallizes in the tetragonal system, space group I4/m with cell constants a = b = 11.710(3) Angstrom, c = 13.003(2) Angstrom, and Z = 4, whereas 2 crystallizes in the orthorhombic system, space group Cmca with cell constants a = 13,543(5) Angstrom, b = 16.054(6) Angstrom, c = 15.6301(9) Angstrom, 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 [W-IV(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 [W-V(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 (S-Co = 3/2), bridged by the diamagnetic [W-IV(CN)(8)](3-) units (S-W(IV) = 0). The magnetic behavior of 2, where the high spin Co(II) ions are bridged by the paramagnetic [W-V(CN)(8)](3-) units [S-W(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.