Thallium-Fluorides Revisited: Crystal Chemistry of TlHF₂, Tl₂[MF₆]·2TlF, and Tl₂[MF₆]·TlCl (M = Si and Ge)

Although the formation of thallium hydrogen fluorides TlH_<i>x</i>F_<i>x</i>+1 (<i>x</i> = 1, 1.5, 2, 3, 5, 6.5, and 7) from TlF and HF was reported in the 1970s, little is known about the corresponding crystal structures. To shed light on the crystal chemistry of the thallium fluorides, we reinvestigated the structure of α-TlHF₂, which was obtained by crystallization of TlF from 50% HF at room temperature. We disclose that β-TlHF₂ is isostructural with α-MHF₂ (M = K, Rb, and Cs), γ-TlHF₂ is isostructural with β-MHF₂ (M = K and Rb), whereas α-TlHF₂ crystallizes in an unusual structure type. During the reaction of TlHF₂ with the glass of the microscope slide, crystals of the previously unknown compound Tl₂[SiF₆]·2TlF were formed. We disclose that the related Tl₂[GeF₆]·2TlF can be obtained by the crystallization of stoichiometric amounts of Tl₂[GeF₆] with TlF from water at room temperature. The crystal structures of α-TlHF₂, Tl₂[SiF₆]·2TlF, Tl₂[SiF₆]·TlCl, Tl₂[GeF₆]·2TlF, Tl₂[GeF₆]·TlCl, and Tl₂[GeF₆] were determined by single-crystal X-ray diffraction analysis. The crystal structures of α-TlF and Tl₂[SiF₆]·<i>x</i>TlF (<i>x</i> = 0, 1) were redetermined at low temperatures.