Synthesis and crystal structure of the disordered modification of Tl6Si2O7

A new compound ??-Tl₆Si₂O₇ has been investigated using the methods of IR spectroscopy and microprobe and X-ray diffraction analysis. The elementary unit parameters were as follows: P6₃/m, a = 9.673(2) Å, c = 3.9169(9) Å, and V = 317.4(1) ų. The structure was resolved by direct methods and corrected until R ₁ = 0.029 (wR ₂ = 0.047) for 240 reflections F _o] ?? 4?? _F . The crystal structure of ??-Tl₆Si₂O₇ contains one symmetrically independent position of the Tl⁺ cation that forms three short (??Tl-O?? = 2.54 Å) bonds and one weak bond (2.93 Å) with the oxygen atom. One can observe a strong disordering of silicon atoms (Si-Si = 0.64 Å). The distorted tetragonal pyramids TlO₄ are linked through silicate tetrahedra into a three-dimensional framework. The interesting feature of the crystal structure of ??-Tl₆Si₂O₇ is in the presence of wide channels occupied by lone electron pairs on Tl⁺ cations. One can also mention that in most of the structures of Tl⁺ oxygen-containing salts the lone pairs are associated into separate parts in the form of micelles in channels of frameworks or other structural cavities.