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

Abstract Crystals of three Pb oxide phosphates, Pb 4 O(PO 4 ) 2 , Pb 8 O 5 (PO 4 ) 2 and Pb 10 (PO 4 ) 6 O, were synthesized from mixtures of PbO and NH 4 H 2 PO 4 heated to 950 °C. The crystal structure of Pb 4 O(PO 4 ) 2 (monoclinic, P 2 1 / c , a = 9.4894(8), b = 7.1402(6), c = 14.4077(13) Å, β = 104.549(2)°, V = 944.91(14) Å 3 ) was solved by direct methods and refined to R 1 = 0.044 ( wR = 0.103). It contains isolated OPb 4 tetrahedra that are linked through Pb—O bonds to O atoms of PO 4 tetrahedra. The crystal structure of Pb 8 O 5 (PO 4 ) 2 (monoclinic, C 2/ m , a = 10.6427(4), b = 10.2078(4), c = 14.3530(6) Å, β = 98.325(1)°, V = 1542.86(11) Å 3 ) was solved by direct methods and refined to R 1 = 0.032 ( wR = 0.068). It is based upon a complex sheet with composition [O 5 Pb 8 ]. The basic element of the sheet is a cluster of composition [O 5 Pb 10 ] that consists of four OPb 4 tetrahedra that share edges. The adjacent [O 5 Pb 10 ] clusters are linked by sharing Pb atoms, resulting in sheets that are parallel to (001). The PO 4 tetrahedra are located in the interlayers between the sheets. The crystal structure of Pb 10 (PO 4 ) 6 O (hexagonal, P 6 3 / m , a = 9.8650(3), c = 7.4306(3) Å, V = 626.25(4) Å 3 ) has been solved by direct methods and refined to R 1 = 0.040 ( wR = 0.106). Pb 10 (PO 4 ) 6 O crystallizes with an apatite-type structure. The structure contains a single O atom that is not part of a PO 4 tetrahedron; it has a site occupancy factor of 0.25 and is located on the 6 3 axis.