CRYSTAL CHEMISTRY OF BASIC LEAD CARBONATES. III. CRYSTAL STRUCTURES OF PB3O2(CO3) AND NAPB2(OH)(CO3)2

Abstract

The crystal structures of synthetic Pb3O2(CO3) and NaPb2(OH)(CO3)(2), have been solved by direct methods and refined to R = 0.062 and 0.024, respectively. Pb3O2(CO3) is orthorhombic, Pnma, a 22.194(3), b = 9.108(1), c = 5.7405(8) Angstrom, V = 1160.4(3) Angstrom, Z = 8. There are four symmetrically distinct Pb2+ cations in irregular coordination polyhedra due to the effect of stereoactive st lone-electron pairs. The structure is based upon double [O2Pb3] chains of [O(1)Pb-4] and [O(2)Pb-4] oxocentred tetrahedra and CO3 groups. The [O2Pb3] chains are parallel to the c axis, whereas the CO3 groups are parallel to the (010) plane. NaPb2(OH)(CO3)(2) is hexagonal, P6(3)mc, a = 5.276(1), c 13.474(4) Angstrom, V= 324.8(1) Angstrom (3) Z = 2 and has been solved by direct methods. There are two symmetrically distinct Pb2+ cations in asymmetric coordination polyhedra due to the effect of stereoactive s(2) lone-electron pairs. The single symmetrically unique Na+ cation is in trigonal prismatic coordination. The structure is based on hexagonal sheets of Pb atoms. Within these sheets, Pb atoms are located at vertices of a 3(6) net, such that each Pb atom has six adjacent Pb atoms that are similar to5.3 Angstrom away. Two sheets are stacked in a close-packing arrangement, forming layers that contain the (CO3) groups. The layers are linked by OH groups that are linearly coordinated by two Pb2+ cations. Naf cations are located between the layers. The structure is closely related to the structures of other lead hydroxide carbonates (leadhillite, macphersonite, susannite, hydrocerussite, 'plumbonacrite').