Crystal-structure determination of pinalite

The crystal structure of pinalite, Pb3WO5Cl2, is orthorhombic Amam, with a = 11.073(2), b = 13.067(3), c = 5.617(1) Angstrom, V = 812.81(3) Angstrom(3 ) and Z = 4. It has been refined to an R index of 0.049 on the basis of 593 unique, observed reflections. There are two crystallographically distinct Pb cations with different coordinations: Pbl has eightfold-coordination wit h ligands of 4 Cl atoms, 4 O atoms, and one stereoactive lone-pair, whereas Pb2 has ninefold-coordination with ligands of 4 Cl atoms and 5 O atoms. Th e W cation has fivefold-coordination with 5 O ligands. The pinalite structu re is layered parallel to (100) with Pb-O-Cl layers interleaved with Pb-W-O layers. Pinalite belongs to the bismuth oxychloride group of structures. T he Pb-O-Cl layer of pinalite duplicates the basic structure of thorikosite and the Pb-W-O layer of pinalite is able to conform to this fundamental cel l through differences in the two Pb coordinations and a unique W coordinati on. Similarly the structures of nadorite and kettnerite are also shown to r eplicate the basic bismuth oxychloride structure.