Preparation and Rietveld refinements of the structures Tl2SnF6 and Tl2TiF6

White powder samples of the new complex fluorides Tl2SnF6 and Tl2TiF6 have been prepared by heating appropriate mixtures of TlF and SnF4 or TiF4 at 30 0 degrees C in a Pt ampoule under an argon atmosphere. Tl2SnF6 and Tl2TiF6 are isotypic to K2GeF6 and crystallize in P (3) over bar m1, with a = 609.0 (1), c = 487.8(1) pm for Tl2SnF6 and a = 596.1(1), c = 485.6(1) pm for Tl2T iF6. The structural parameters have been refined by Rietveld analysis from powder data. Calculations of the Madelung part of the lattice energy (MAPLE ) and band structure calculations were performed, to discuss the chemical b onding and the stereochemical activity of the lone pair at Tl+. (C) 2000 El sevier Science Ltd. All rights reserved.