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

Two Fe-II-based molybdenum polycyanides, Fe-2[Mo-III(CN)(7)]. 8H(2)O and [Fe-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, space group I422. There are two molybdenum sites in a distorted square antiprism arrangement, each site being surrounded by eight CN-Fe linkages. The distorted octahedral iron site is formed by four NC-Mo linkages and two water molecules in apical positions. The structure is three-dimensional and highly symmetrical. The magnetic characteristics of these two compounds were compared. 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 magnetic order, obviously due to the contribution of the diamagnetic Mo-IV which suppresses the propagation of magnetic interaction between adjacent iron(II) ions through CN bridges. The results are discussed in the light of the single-crystal structural features of [Fe-2(H2O)(4)][Mo-IV(CN)(8)]. 4H(2)O.