Crystal structure of a novel synthetic compound, Pb2O(OH)I, and structure refinement of ‘iodolaurionite’, Pb(OH)I: hydroxo- and oxocentred units in Pb minerals and synthetic compounds

Abstract

AbstractYellow needles of 'iodolaurionite', Pb(OH)I, and a novel compound Pb2O(OH)I, have been prepared by hydrothermal reactions of PbO and PbI2 at 170°C. The crystal structure of 'iodolaurionite', Pb(OH)I (orthorhombic, Pnma, a = 7.8244(8), b = 4.2107(4), c = 10.4724(10) Å, V = 345.03(6) Å3, Z = 4) has been refined to R1 = 0.041 for 129 independent observed reflections. The structure is based on the OHPb3 triangles sharing common edges to produce single [OHPb]+ chains extending along the b axis and parallel to the ab plane. The three-dimensional integrity of the structure is provided by the Pb–I bonds and the O–H···I hydrogen bonding. The structure is isotypic with that of laurionite, Pb(OH)Cl. The crystal structure of Pb2O(OH)I (monoclinic, C2/m, a = 13.711(3), b = 4.0975(10), c = 9.584(2) Å, β = 110.64(1)°, V = 503.9(2) Å3, Z = 4), has been solved by direct methods and refined to R1 = 0.053 for 586 independent observed reflections. In the structure of Pb2O(OH)I, O(1)Pb4 tetrahedra link together by sharing edges and corners to form [OPb2]2+ chains similar to those observed in sidpietersite. The O(2) atoms belong to hydroxyl groups attached to both sides of the chains to produce novel [O(OH)Pb2]+ 1D units. The [O(OH)Pb2]+ units are extended parallel to the b axis and lie within the bc plane. The [O(OH)Pb2]+ units are linked together via hydrogen bonding in the (100) plane and by weak Pb–I bonds in the [100] direction. The [O(OH)Pb2]+ bands can be obtained from the [OPb] layer of OPb4 tetrahedra present in the structure of tetragonal PbO (litharge). The continuous [OPb] layer has to be broken into [O2Pb2] bands containing 3- and 4-coordinated O atoms in the 1:1 ratio with subsequent protonation of the 3-coordinated O sites. Relations of Pb(OH)I and Pb2O(OH)I to known Pb hydroxy- and oxyhalides are described briefly.