Solvothermal Synthesis and Crystal Structure of Te₈[U₂Br₁₀], Containing a Polymeric Chalcogen Cation (Te₈²⁺)_n

Under solvothermal conditions, the reaction of Te, TeBr₄ and UBr₅ in SiBr₄ at 200?C yields Te₈[U₂Br₁₀] as silvery crystals. The crystal structure (triclinic, P&1macr;, a = 900.8(4), b = 1205.1(5), c = 1366.0(6) pm, α = 80.93(4)?, β = 76.83(3)?, γ = 78.84(3)?, Z = 2) is built of one-dimensional polymeric (Te₈²⁺)_n cations consisting of boat-shaped Te₆ rings, which are linked by Te₂ bridges. The anions [U₂Br₁₀^2-]_n are also polymeric, consisting of edge sharing UBr₇ pentagonal bipyramids [UBr₃Br_4/2^2-]_n and contain U(IV). Both chains are parallel to each other and run along the crystallographic a-axis. The cation represents a formerly unknown isomer of Te₈²⁺ ions. So far, Te₈²⁺ has been known as molecular clusters in Te₈[MCl₆](M = Zr, Hf, Re) and (Te₈)(Te₆)[WCl₆]₄, or in form of linked bicyclic monomers that are present in Te₈[WCl₆]₂. A polymeric chain-like form closely related to Te₈[U₂Br₁₀] was found in Te₈[Bi₄Cl₁₄].