Hepta/octa cyanomolybdates with Fe2+: influence of the valence state of Moon the magnetic behavior

Two Fe-II-based molybdenum polycyanides, Fe-2[Mo-III(CN)(7)]. 8H(2)O and [F e-2(H2O)(4)][Mo-IV(CN)(8)]. 4H(2)O, have been synthesized. The compound [Fe -2(H2O)(4)][Mo-IV(CN)(8)]. 4H(2)O crystallizes in the tetragonal system, sp ace group I422. There are two molybdenum sites in a distorted square antipr ism arrangement, each site being surrounded by eight CN-Fe linkages. The di storted octahedral iron site is formed by four NC-Mo linkages and two water molecules in apical positions. The structure is three-dimensional and high ly symmetrical. The magnetic characteristics of these two compounds were co mpared. Fe-2[Mo-III(CN)(7)]. 8H(2)O orders below 65 K as a ferrimagnet, but [Fe-2(H2O)(4)][Mo-IV(CN)(8)]. 4H(2)O shows no evidence of long-range magne tic order, obviously due to the contribution of the diamagnetic Mo-IV which suppresses the propagation of magnetic interaction between adjacent iron(I I) ions through CN bridges. The results are discussed in the light of the s ingle-crystal structural features of [Fe-2(H2O)(4)][Mo-IV(CN)(8)]. 4H(2)O.