CRYSTAL-STRUCTURE OF SR4ZN3F14 - A NEW STOICHIOMETRY IN MF2-M'F2 SYSTEMS

The fluoride Sr4Zn3F14 has been characterized during the study of the SrF2 - ZnF2 binary system using X-ray powder diffraction and different ial thermal analysis. Its crystal structure was determined from single crystal X-ray diffraction data and refined to a conventional R = 0.04 1 (R(w) = 0.048) for 1308 unique reflections with I > 3 sigma(I). It c rystallizes in the monoclinic system with the cell parameters a = 6.74 3(1) angstrom , b = 11.683(1) angstrom, c = 7.191(2) angstrom, beta = 90.02(1)degrees, space group Cm (n-degrees 8), Z = 2. The structure ma y be regarded as being composed of alternated layers of comer-sharing square pyramids of Zn and face-sharing distorted tricapped trigonal pr isms of Sr linked together by sharing vertices and isolated columns ma de up of 9-coordinate strontiums in tricapped trigonal prism environme nts.