CRYSTAL-STRUCTURE DETERMINATIONS OF 4 MON OCLINIC WEBERITES NA(2)M(II)M(III)F(7) (M(II)=FE,CO, M(III)=V,CR)

By solid state reaction of the binary fluorides single crystals of the following weberites were prepared and their monoclinic structure (spa ce group C2/c, Z = 16) determined by X-ray methods: Na2FeVF7 (a = 1271 .0(3), b = 742.9(1), c = 2471.6(5) pm, beta = 100.03(3)degrees; R(i) = 0.043 (1545 Reflexe); Fe-F = 203.8, V-F = 193.0 pm); Na2FeCrF7 (a = 1 262.5(3), b = 739.1(1), c = 2460.5(5) pm, beta = 99.93(3)degrees; R(1 ) = 0.029 (2340); Fe-F = 203.6, Cr-F = 190.5 pm); Na2CoVF7 (a = 1270.3 (5), b = 739.1(3), c = 2465.1(10)pm, beta = 100.02(3)degrees; R(i) = 0 .028 (2250); Co-F = 201.6, V-F = 193.6 pm); Na2CoCrF7 (a = 1257.8(3), b = 733.5(1), c = 2441.5(5)pm, beta = 99.64(3)degrees; R(i) = 0.030 (2 227); Co-F = 201.2, Cr-F = 190.2 pm). Concerning the above average dis tances within the distorted [MF(6)] octahedra and the shape of [NaF8] coordination details are given and discussed.