The crystal structure of Ca2AlF7

Abstract

Abstract The existence of Ca2AlF7 is confirmed. Lattice constants (Guinierde Wolff photographs, CuKα 1) are a = 7.685 Å; b = 6.998 Å; c = 9.549 Å; d rö = 3.10g cm−3; d pyk = 3.07g cm−3; Z = 4; space group P nma. The structure was determined using 826 unique reflections [4-circle diffractometer PW1100, MoKα]; the refinement with anisotropic temperature factors led to R w = 0.039. According to Ca2F[AlF6] nearly octahedral groups [AlF6] are linked by Ca(1) and Ca(2). The ‘lone’ F(1) is coordinated by 3 Ca; Ca(1) has coordination number 7 and Ca(2) 7 + 1. Details of the structure are discussed using the Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN.