Tl5SnF9 and Tl5TiF9: The first [Tl5F3](2+) layers in novel thallium(I) fluoridefluorometallates(IV)

Tl5TiF9 and Tl5SnF9 were prepared via solid state reactions from mixed powd ers of the TlF and SnF4 or TiF4, respectively, in platinum crucibles under Ar (573 K). Both fluorides are colourless, transparent and extremely hygros copic. The compounds Tl5MF9 (M = Sn, Ti) crystallize in a new structure typ e in Pbam (Nr.55) with a = 1117.6 pm, b = 684.8 pm, c = 799.2 pm for Tl5SnF 9 and a = 1111.4 pm, b = 674.7 pm, c = 783.2 pm for Tl5TiF9. Characteristic building units in the new Thallium(I) fluoridefluorometallat es(IV) are [Tl5F3](2+) sheets found for the first time, which are connected via [MF6](2-) octahedra (M = Ti, Sn) to a threedimensional network (d(Sn-F ) = 194-197 pm, d(Ti-F) = 186-187 pm). The monovalent Tl are coordinated by 8F with distances Tl-F between 264 and 334 pm. The chemical bonding is dis cussed on the basis of Extended-Huckel band structure calculations.