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THE CRYSTAL STRUCTURE OF Pb₈O₅(OH)₂Cl₄, A SYNTHETIC ANALOGUE OF BLIXITE?

Sergey V. Krivovichev^1, and Peter C. Burns²

¹ Department of Crystallography, St. Petersburg State University, University Emb. 7/9, RU–199034 St. Petersburg, Russia
² Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, Indiana 46556-0767, USA

E-mail address: skrivovi{at}mail.ru

The crystal structure of hydrothermally synthesized Pb₈O₅(OH)₂Cl₄ [monoclinic, C2/c, a 26.069(5), b 5.8354(11), c 22.736(4) Å, ß 102.612(6)°, V 3375.3(11) ų] has been determined and refined to R₁ = 0.047 with data collected from a crystal twinned on (100). There are eight symmetrically independent Pb²⁺ cations in the structure, with each having a strongly distorted coordination polyhedron due to the presence of stereochemically active pairs of s² lone electrons on the Pb²⁺ cations. The structure is based upon [O₅Pb₈] sheets parallel to (100) formed by edge-sharing (OPb₄) oxocentered tetrahedra. Hydroxyl groups form two short (OH)–Pb bonds that result in (OH)Pb₂ dimers attached to the [O₅Pb₈] sheets. The chlorine anions are located between the {[O₅Pb₈](OH)₂} sheets, providing three-dimensional linkage of the structure. The structure is closely related to other structures based on PbO-type defect sheets. On the basis of chemical composition and powder X-ray-diffraction data, we suggest that Pb₈O₅(OH)₂Cl₄ is a synthetic analogue of blixite.

Keywords: lead oxide chloride, blixite, oxocentered tetrahedra, crystal structure.

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