Crystal chemistry of lead oxide phosphates: crystal structures of Pb4O(PO4)2, Pb8O5(PO4)2 and Pb10(PO4)6O

Abstract

Abstract Crystals of three Pb oxide phosphates, Pb4O(PO4)2, Pb8O5(PO4)2 and Pb10(PO4)6O, were synthesized from mixtures of PbO and NH4H2PO4 heated to 950 °C. The crystal structure of Pb4O(PO4)2 (monoclinic, P21/c, a = 9.4894(8), b = 7.1402(6), c = 14.4077(13) Å, β = 104.549(2)°, V = 944.91(14) Å3) was solved by direct methods and refined to R1 = 0.044 (wR = 0.103). It contains isolated OPb4 tetrahedra that are linked through Pb—O bonds to O atoms of PO4 tetrahedra. The crystal structure of Pb8O5(PO4)2 (monoclinic, C2/m, a = 10.6427(4), b = 10.2078(4), c = 14.3530(6) Å, β = 98.325(1)°, V = 1542.86(11) Å3) was solved by direct methods and refined to R1 = 0.032 (wR = 0.068). It is based upon a complex sheet with composition [O5Pb8]. The basic element of the sheet is a cluster of composition [O5Pb10] that consists of four OPb4 tetrahedra that share edges. The adjacent [O5Pb10] clusters are linked by sharing Pb atoms, resulting in sheets that are parallel to (001). The PO4 tetrahedra are located in the interlayers between the sheets. The crystal structure of Pb10(PO4)6O (hexagonal, P63/m, a = 9.8650(3), c = 7.4306(3) Å, V = 626.25(4) Å3) has been solved by direct methods and refined to R1 = 0.040 (wR = 0.106). Pb10(PO4)6O crystallizes with an apatite-type structure. The structure contains a single O atom that is not part of a PO4 tetrahedron; it has a site occupancy factor of 0.25 and is located on the 63 axis.