Crystal structure of Pb_3O_2(OH)Br, a Br-analogue of damaraite

摘要

The crystal structure of Pb_3O_2(OH)Br (orthorhombic, Pmc2_1, a = 5.8447(8), b = 7.0715(10), c = 15.309(2) A, V = 632.75(15) A~3) has been solved by direct methods and refined to R_1 = 0.046 (w R = 0.077). The structure is based on (O_2Pb_3) chains of edge-sharing OPb_4 oxocentered tetrahedra that extend parallel to the a axis and occur in two orientations inclined to each other by approx 50 deg. The (O_2Pb_3) chains are linked through OH(3) groups to form an (Pb_3O_2)(OH) sheet that is parallel to (010). Additional OH(4) groups are attached to the (O_2Pb_3) chains. The OH groups form two short (OH)-Pb bonds that results in (OH)Pb_2 dimers.