Crystal chemistry of natural and synthetic lead oxohalides: II. Crystal structure of Pb7O4(OH)4Br2

Crystals of lead oxobromide Pb(7)O(4)(OH)(4)Br(2) have been synthesized by hydrothermal method. The structure of the new compound has been studied with X-ray single-crystal diffraction analysis. The compound is monoclinic, space group C112(1); unit-cell dimensions are a = 5.852(4), b = 13.452(7), c = 19.673(9) A..., gamma = 90.04A degrees, V = 1548.7(15) A...(3). The structure has been solved by direct methods and refined to R (1) = 0.1138 for 1847 observed Pb(7)O(4)(OH)(4)Br(2) unique reflections. The structure contains seven symmetrically independent bivalent Pb atoms. The coordination polyhedrons of Pb are strongly distorted due to stereochemical activity of unshared electron pair 6s (2). Oxygen atoms are tetrahedrally coordinated by four Pb(2+) cations with the formation of oxocentered tetrahedrons OPb(4). The compound is based on [O(2)Pb(3)](2+) double chains formed by OPb(4) tetrahedrons. (OH)Pb(2) dimers combine the [O(2)Pb(3)](2+) chains into 3D framework. Channels in the framework are parallel to [100] and are occupied by Br anions.