A crystal structure refinement of uralolite, Ca2Be4(PO4)3(OH)3•5H2O, from Weinebene, Austria

The crystal structure of uralolite, Ca2Be4(PO4)(3)(OH)(3)center dot 5H(2)O, from the spodumene deposit of Weinebene, Carinthia, Austria, has been refined with X-ray single crystal data gathered on a CCD diffractometer. Uralolite is monoclinic, space group P2(1)/n, a = 6.553(1), b = 16.005(3), c = 15.979(3) angstrom, beta = 101.63(1)degrees, V = 1641.5(5) angstrom(3). While previously only isotropic displacement parameters and no hydrogen atom positions were reported for uralolite, now anisotropic displacement parameters were used for non-hydrogen atoms and hydrogen atoms were located and refined yielding R-1 = 0.038 for 3909 observed reflections. Uralolite is built up from corrugated layers [Be-4(PO4)(3)(OH)(3)](4-) parallel to (010), which contain Z-shaped groups of four BeO4 tetrahedra sharing corners via three OH groups and are further crosslinked by PO4 tetrahedra. Two Ca atoms in Ca(O-phosphate)(5)(H2O)(2) coordination and an interstitial water molecule link these layers along [010]. The OH groups and the Ca-bonded H2O molecules are all involved in hydrogen bonds with O center dot center dot center dot O distances of 2.780(2) - 3.063(2) angstrom and O-H center dot center dot center dot O angles of 150(1) - 179(1)degrees excluding a bifurcated bond. The interstitial water molecule displays a distorted tetrahedral environment of O atoms and accepts and donates each two hydrogen bonds. The crystal structure exhibits a C2/c pseudosymmetry for the [Be-4(PO4)(3)(OH)(3)](4-) layers and the Ca atoms. However, the disposition of the water molecules and an asymmetric hydrogen bond pattern involving OH groups as well as H2O molecules are decisive for the lowering of the symmetry of the structure to the true space group P2(1)/n.