Crystal and molecular structure of tetrachlorophosphorus(V) hexachlorouranate(V)

The crystal structure of tetrachlorophosphorus(V) hexachlorouranate(V), PCl⁺₄.UCl^?₆, has been solved with 2492 independent F(hkl) collected by necessity from one component of a bicrystal; all crystals prepared were twinned. The structure is triclinic, space group P$\text{1}$, with a = 7.038(4), b = 7.373(4), c = 13.706(8) Å, α = 89.38(3), β = 88.80(3), γ = 105.20(3)°, with Z = 2. The two components of the bicrystal, in the volume ratio of 2.5 to 1, had their reciprocal lattice spots sufficiently separated to allow collection of the data set from component 1 with AgKα radiation (λ = 0.5608 Å). A model was derived from the Patterson synthesis and refined by least squares to R = Σ(|Fo|-|F_C|)/Σ|Fo| = 0.146. The structure was confirmed by a final (ρ_o-ρ_c) synthesis. The structure is an assembly of octahedral U(1)Cl^?₆, U(2)Cl^?₆ and tetrahedral PCl⁺₄ groups. The chlorine atom array is hexagonal close-packed, while the polyhedra are regular within the experimental errors. The structure is isomorphous with the transition metal analogues PCl₅.NbCl₅ and PCl₅.TaCl₅.