Crystal chemistry of natural and synthetic lead oxohalides: II. Crystal structure of Pb7O4(OH)4Br2
Crystals of lead oxobromide Pb7O4(OH)4Br2 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 C1121; unit-cell dimensions are a = 5.852(4), b = 13.452(7), c = 19.673(9) Å, γ = 90.04°, V = 1548.7(15) Å3. The structure has been solved by direct methods and refined to R1 = 0.1138 for 1847 observed Pb7O4(OH)4Br2 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 6s2. Oxygen atoms are tetrahedrally coordinated by four Pb2+ cations with the formation of oxocentered tetrahedrons OPb4. The compound is based on [O2Pb3]2+ double chains formed by OPb4 tetrahedrons. (OH)Pb2 dimers combine the [O2Pb3]2+ chains into 3D framework. Channels in the framework are parallel to  and are occupied by Br anions.
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