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

We have synthesized the octacyanoniobate-based cyano-bridged 3D ferromagnet {[Fe-II(H2O)(2)](2)[Nb-IV(CN)(8)]center dot 4H(2)O}(n) 1 and characterized structurally, spectroscopically (XANES/EXAFS, IR, UV-Vis, Resonance Raman, Fe-57 Mossbauer spectroscopy) and magnetically. 1 crystallizes in the tetragonal system, space group I4/m, a = 11.989(5)angstrom, c = 13.237(5)angstrom, V = 1902.6(13)angstrom(3). 3D coordination architecture comprises two types of Nb-IV-C-N-Fe-HS(II) (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 FeII (S = 2) magnetic moments. The molecular field model simulation reproduces well the M(T) curve and Tc value with one average exchange coupling constant J(FeNb) = + 8.1 cm(-1).