Crystalline and Glassy Phases in the Ternary System Tl/Bi/Cl: Synthesis and Crystal Structures of the Thallium(I) Chloridobismutates(III) Tl 3 BiCl 6 and TlBi 2 Cl 7

Slow cooling of melts composed of TlCl and BiCl 3 allows for the isolation of the compounds Tl 3 BiCl 6 ( 1 ) and TlBi 2 Cl 7 ( 2 ). Compound 1 is formed by sublimation at 480 °C from the black melt of 3 TlCl + 1 BiCl 3 as colourless crystals. The crystal structure determination (tetragonal, P 4 2 / m ) consists of nearly regular octahedral [BiCl 6 ] 3– anions and two independent Tl + cations, which have coordination number 8 in form of a slightly distorted cube and 10 in form of an Edshamar polyhedron, respectively. The structure is not isotypic with the recently reported naturally occurring form of Tl 3 BiCl 6 , the mineral steropesite. Compound 2 is obtained from a dark red melt of composition TlCl + 2 BiCl 3 . On rapid cooling, this melt solidifies to a metastable dark red glass which at ambient temperature crystallises to a light amber crystalline powder within some weeks. The structure of 2 was determined by powder diffraction (triclinic, P \bar{1} ). A distinct lone pair effect is present causing an irregular coordination on the two independent bismuth atoms. Taking Bi–Cl bonds up to 3.5 Å into account, both bismuth atoms gain coordination number seven. 203 Tl and 205 Tl solid state NMR and XANES spectra on the Bi and Tl‐L III edges of both glassy and crystalline TlBi 2 Cl 7 show that a close structural similarity exists between both forms. In contrast, the Raman spectra show distinct differences in the bands of the Bi–Cl vibrations region.