The structure of synthetic tinsleyite K[Al2(PO4)2(OH)(H2O)]•H2O

Synthetic tinsleyite K[Al-2(PO4)(2)(OH)(H2O)]. H2O has been obtained by the reaction of gibbsite with a potassium-phosphate solution of pH = 7 at 423 K within five days. A single crystal X-ray structure analysis has shown that synthetic tinsleyite is isotypic with the mineral leucophosphite K[Fe-2(PO4)(2)(OH)(H2O)]. H2O. Crystal data: monoclinic space group P2(1) / n, a = 949.9(2), b = 950.3(2), c = 953,5(2) pm, beta = 103.26(3)degrees, Z = 4. The structure of tinsleyite consists of tetranuclear Al4O2 units formed by a central pair of edge sharing AlO6 octahedra, to which two additional AlO6 octahedra are attached sharing corners. These units are crosslinked by phosphate ions to a three dimensional framework structure with tunnels along [010], occupied by potassium cations. While one type of water molecules is attached to Al, a second type is fixed in the structure by hydrogen bonds only. As a consequence two steps for thermal loss of water at 341 K and 471 K are observed.