Iron(II)-octacyanoniobate(IV) ferromagnet with T(C) 43 K.

We have synthesized the octacyanoniobate-based cyano-bridged 3D ferromagnet {[Fe(II)(H(2)O)(2)](2)[Nb(IV)(CN)(8)].4H(2)O}(n) and characterized structurally, spectroscopically (XANES/EXAFS, IR, UV-Vis, Resonance Raman, (57)Fe Mössbauer spectroscopy) and magnetically. crystallizes in the tetragonal system, space group I4/m, a = 11.989(5) A, c = 13.237(5) A, V = 1902.6(13) A(3). 3D coordination architecture comprises two types of Nb(IV)-C-N-Fe(II)(HS) (HS = high spin) linkages with Fe-N-C angles of 154.5 degrees and 167.5 degrees . The XANES/EXAFS spectra at Fe:K and Nb:K lines confirm the presence of Nb(IV)-C-N-Fe(II) linkages. Magnetic measurements reveal ferromagnetic ordering below T(c) = 43 K with some non-collinearity of Nb(IV) (S = 1/2) and Fe(II) (S = 2) magnetic moments. The molecular field model simulation reproduces well the M(T) curve and T(c) value with one average exchange coupling constant J(FeNb) = + 8.1 cm(-1).