Tl2Ch22- (Ch = Se and/or Te) Anions: X-ray Crystal Structures and Raman Spectra of (2,2,2-crypt-K+) 2Tl2Se22- and (2,2,2-crypt-K +)2Tl2Te22- and Solution 77Se, 203Tl, and 205Tl NMR Spectroscopic and Theoretical Studies

The seleno- and tellurothallate(I) anions Tl2Ch2^2- (Ch = Se and/or Te) and the ⁷⁷Se-enriched Tl2Se2^2- anion have been obtained by extraction of the alloys MTlCh (M = Na, K; Ch = Se, Te), KTlSe0.5Te0.5, and ⁷⁷Se-enriched KTlSe in ethylenediamine and liquid NH3 and in the presence of a stoichiometric excess of 2,2,2-crypt with respect to M⁺. The butterfly-shaped Tl2Ch2^2- anions were characterized in solution by ⁷⁷Se, ²⁰³Tl, and ²⁰⁵Tl NMR spectroscopy, Raman spectroscopy, and X-ray crystallography in (2,2,2-crypt-K⁺)2Tl2Ch2 ^2-. The energy-minimized structures of the Tl2Ch2^2- (Ch = Se and/or Te) anions were calculated by using density functional theory calculations confirming the nonplanar geometries of all three anions, which are compared with those of the presently unknown In2Ch2^2- (Ch = Se, Te) anions. The magnitudes of the relativistically corrected reduced coupling constants, (KTl-Ch)RC, are consistent with essentially pure p-bonded rings whereas the magnitudes of (KTl-Tl)RC suggest significant s electron density along the Ti⋯Ti axes and is confirmed by theory. Density functional theory calculations were also used to assign the solid-state vibrational spectra of Tl2Se2^2- and Tl2Te2^2-. The variation of the ²⁰⁵Tl-²⁰³Tl spin-spin coupling constants with solvent and temperature, the differences between the calculated and experimentally determined fold angles, and the low experimental and calculated vibrational frequencies of the anion deformation modes indicate that the anion geometries are significantly influenced by environmental factors.