On the Structure of Tl2Pb(SO4)2 and Crystal Chemistry of Thallium-Containing Sulfates

Single crystal of a thallium-containing sulfate Tl2Pb(SO4)(2) was prepared through hydrothermal crystallization starting from Tl2CO3, Pb(NO3)(2) and H2SO4. The crystal structure was solved from single-crystal X-ray diffraction data: Tl2Pb(SO4)(2) crystallizes in space group R m with lattice parameters of a=5.5955(2) & Aring;, c=22.1001(9) & Aring;, and Z=3, which is also corroborated by Rietveld refinement on X-ray powder data. The crystal structure can be regarded as [Pb(SO4)(2)](2-) sheets intercalated by double layers of Tl+ along the <bold>c</bold>-axis. From a mineralogical perspective, Tl2Pb(SO4)(2) belongs to the palmierite family and can further be classified within palmierite-supergroup. Validation of the structure models was carried out utilizing various concepts including Bond Valence (BV), Charge Distribution (CD) and Madelung Part of Lattice Energy (MAPLE). Notably, a contrast in stereochemical activity of 6s(2) lone electron pair (LEP) between Tl+ and Pb2+ is interpreted in terms of bonding behaviours as well as Wang-Liebau Eccentricity (WLE) parameters. Moreover, an extensive investigation into the crystal chemistry of thallium-containing sulfates was conducted for the first time, focusing on the coordination environment and bonding behaviour of Tl+ and corresponding WLE parameters. A comparative analysis of these structurally related compounds including Tl2Pb(SO4)(2), Tl3H(SO4)(2), TlBi(SO4)(2), TlIn(SO4)(2), TlRh(SO4)(2), and TlAl(SO4)(2) was delineated.