The crystal structure of vlodavetsite, AlCa 2 (SO 4 ) 2 F 2 Cl.4H 2 O

Absract The crystal structure of vlodavetsite, A1Caz(SOa)2FzC1.4HzO, has been determined, space group 14/m, a = 6.870(1), c = 13.342(2) A, Z = 2, Dx = 2.35 g/cm 3. The polyhedron cation chains are parallel to [001] and consist of couples of distorted Ca octahedra alternating with one distorted A1 octahedron rotated through 24 ~ with respect to the former. The chains are linked by SO4-tetrahedra so that all of the four tetrahedron oxygen atoms take part in coordination of Ca atoms to form a distorted octahedron with C1 and F atoms. The A1 coordination polyhedron consists of two F atoms and four oxygen atoms belonging to water molecules. There is a specific interaction via hydrogen bonds between oxygen atoms of SO4-tetrahedra and water molecules.