CATION DISTRIBUTION AND LOCAL CONFIGURATION OF FE2+ IONS IN STRUCTURALLY NONEQUIVALENT LATTICE SITES OF HETEROMETALLIC FE(II)/M(II) (M = MN, CO, NI, CU, ZN) DIAQUADIFORMATO COMPLEXES

57Fe Mössbauer investigations are carried out on a wide series of heterometallic diaquadiformato Fe(II)/M(II) complexes with M = Mn, Co, Ni, Cu, and Zn to provide a local picture of the coordination environment of the 57Fe2+ ions as a function of (i) the nature of the host cation and (ii) the relative amounts of both metals in the matrix (between 50 and 0.25 at.% Fe). Information is obtained on the quantitative distribution of both metals between the two structurally nonequivalent lattice sites and on the local geometry around the dopant atom in each crystal site. In the mixed Fe-Cu complexes. Fe2+ ions are preferentially incorporated in the tetrahydrated site; in Cu-rich FexCu1-x(HCO2)2· 2H2O, the 57Fe2+ ions located in the hexaformato-coordinated site are surrounded by an axially compressed octahedron of formate ligands which contrasts with the elongated configuration observed in the pure iron compound and in the other mixed systems. Semiquantitative estimations of the tetragonal field splitting and of the extent of metal-ligand interactions are proposed from the temperature dependence of the quadrupole splitting values. © 1993 Academic Press, Inc.