Crystal chemistry of basic lead carbonates. III. Crystal structures of Pb3O2(CO3) and NaPb2(OH)(CO3)(2)

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, respectiv ely. Pb3O2(CO3) is orthorhombic, Pnma, a 22.194(3), b = 9.108(1), c = 5.740 5(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 grou ps 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 ha s been solved by direct methods. There are two symmetrically distinct Pb2cations in asymmetric coordination polyhedra due to the effect of stereoact ive s(2) lone-electron pairs. The single symmetrically unique Na+ cation is in trigonal prismatic coordination. The structure is based on hexagonal sh eets 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 simil ar to5.3 Angstrom away. Two sheets are stacked in a close-packing arrangeme nt, forming layers that contain the (CO3) groups. The layers are linked by OH groups that are linearly coordinated by two Pb2+ cations. Naf cations ar e located between the layers. The structure is closely related to the struc tures of other lead hydroxide carbonates (leadhillite, macphersonite, susan nite, hydrocerussite, 'plumbonacrite').