Crystallography between Kiel and St. Petersburg: review of collaboration and the crystal structure of [Tl5(SiO4)(OH)]2[Tl6(SO4)(OH)4].

In this contribution, we briefly review the results of collaborative research between crystallography groups in St. Petersburg and Kiel, and report on the synthesis and crystal structure of Tl16(SiO4)2(SO4)(OH)6 ( 1), a new and unusual compound obtained from highly-alkaline TlOH solution. Its structure [monoclinic, C2/ m, a = 28.7140(18), b = 7.3686(5), c = 7.4426(5) Å, β = 104.653(2)°, V = 1523.50(17) Å3, R1 = 0.066 for 1528 independent observed reflections] can be described as an alternation of electroneutral [Tl5(SiO4)(OH)] and [Tl3(SO4)0.5(OH)2] layers. The [Tl5(SiO4)(OH)] layer consists of Tl(1)O4 tetragonal pyramids sharing common corners with the SiO4 tetrahedra to form pseudotetragonal [Tl(SiO4)]3- layers capped by OH(1)-centered [(OH)Tl4] square pyramids with the Tl(2) and Tl(3) atoms in their apices. The [Tl3(SO4)0.5(OH)2] layers contain OH(2)- and OH(3)-centered [(OH)Tl4] square pyramids sharing common edges to form large (∼ 7.4 × 7.4 Å) cavities occupied by disordered (SO4) tetrahedra. The electroneutral character of the [Tl5(SiO4)(OH)] and [Tl6(SO4)(OH)4] layers allows us to suggest that the phases with these chemical compositions may form as independent compounds in highly alkaline Tl-bearing systems. [ABSTRACT FROM AUTHOR]