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Cesium; Thallium; Cluster compounds; Crystal structures; Physical properties
Abstract:
Cs(10)Tl(6)TtO(4) (Tt = Si, Ge) and Cs(10)Tl(6)SnO(3) were synthesized by the reaction of appropriate starting materials at 623-673 K, followed by fast cooling or quenching to room temperature, in arc-welded tantalum ampoules. According to single-crystal X-ray analyses, the compounds crystallize in new structure types (Cs(10)Tl(6)TtO(4) (Tt = Si, Ge), P2(1)/c and Cs(10)Tl(6)SnO(3), Pnma), consisting of [Tl(6)](6) clusters, which can be characterized as distorted octahedra compressed along one of the fourfold axes of an originally unperturbed octahedron, and [SiO(4)](4), [GeO(4)](4) or [SnO(3)](4) anions. The oxotetrelate thallides can be regarded as "double salts", which consist of Cs(6)Tl(6) on one side and respective oxosilicates, -germanates and -stannates on the other, showing almost not any direct interaction between the two anionic moieties, as might be expressed e. g. by the formula [Cs(6)Tl(6)][Cs(4)SiO(4)]. In contrast to the silicon and germanium compounds, where the oxidation state of the tetrel atom is unambiguously 4+, for the threefold coordinated tin atom in Cs(10)Tl(6)SnO(3) an oxidation state of 2+ has to be assumed. Thus, the latter reveal further evidence that the so called "hypoelectronic" [Tl(6)](6) cluster does not require additional electrons and is intrinsically stable. The distortion of [Tl(6)](6) can be understood in terms of the Jahn-Teller theorem. According to magnetic measurements all title compounds are diamagnetic.
