New Lead Orthosilicate {Pb4(О(ОН)2)}[SiO4] with a Framework of Anion-Centered Pb Tetrahedra Related to Sodalite

Abstract

New lead silicate {Pb₄(О(ОН)₂)}[SiO₄] was synthesized under hydrothermal conditions and structurally characterized, sp. gr. P2₁3, а = 8.9756(13) Å. According to the commonly used classification, the new compound belongs to orthosilicates. In the crystal structure, isolated SiO₄ tetrahedra are located between numerous Pb atoms. The structure can be considered as an anion-centered positively charged zeolite-like framework composed of {O₃Pb₇}⁸⁺ clusters, which are linked to each other and include three edge-sharing (OPb₄)⁶⁺ tetrahedra with one common vertex. The formula of this positively charged antiframework is {O(ОН)₂Pb₄}⁴⁺, and its cavities are occupied by negatively charged [SiO₄]^4– tetrahedra. This framework is similar to that of sodalite when relating the sites to the centers of gravity of the {O₃Pb₇}⁸⁺ clusters.