Preparation and Crystal Structure of the Strontium Aluminium Fluoride Sr5Al2F16

Single crystals of Sr₅Al₂F₁₆ crystallize in colourless translucent plates and have been prepared by solid state synthesis, starting from stoichiometric mixtures of the binary fluorides. The crystal structure has been determined and refined from single crystal diffractometer data (orthorhombic, space group Ccca (no. 68), a = 7.4488(4) Å, b = 12.4714(7) Å, c = 14.1411(8) Å, V = 1313.67(13) ų, Z = 4, RF ² > 2σ(F ²)] = 0.025; wR2(F ² all) = 0.056, 971 structure factors, 56 parameters) and can be derived from a slightly distorted c.c.p. arrangement where 7/8 of the c.c.p. positions are occupied by the metal atoms. The main features of the structure are AlF₆ octahedra and SrF₈ polyhedra with mean distances d(Al–F) = 1.791 Å and d(Sr–F) = 2.531 Å, respectively.