New Oligomeric Tungsten-Chalcogenide Anions

Upon acidification with acetic acid and precipitation from methanol solution with PPh⁺₄, the WSe^2-₄ anion affords [PPh₄]₂-[(W₃Se₉)_0.46(W₃Se₃O)_0.54]. This compound crystallizes in the triclinic space group P1 with a = 9.085 (5) Å, b = 10.666 (4) Å, c = 13.407 (3) Å, α = 87.22 (2)°, β = 86.30 (3)°, γ = 84.11 (3)°, and Z = 1. The W₃Se^2-₉ ion shows square-pyramidal coordination of Se atoms about the central W atom and tetrahedral coordination about the outer W atoms. The anion WS^2-₄ when acidified with H₂SO₄ yields W₃S^2-₈, which may be isolated as its PPN⁺ salt. [PPN]₂[W³S₈] crystallizes in the triclinic space group P1 with a = 11.548 (2) Å, b = 15.175 (5) Å, c = 22.181 (5) Å, α = 104.90 (2)°, β = 90.80 (2)°, γ = 110.31 (2)°, and Z = 2. The central W atom has approximately square-planar coordination of S atoms, and the outer W atoms have tetrahedral coordination. Heating WSe^2-₄ in acetonitrile yields a complex mixture of anions that includes W₃Se^2-₉, W₂Se^2-₉, and W₂Se^2-₁₀. Addition of elemental Se to the reaction mixture affords two isomers of W₂Se^2-₁₀ and other dimers in smaller concentrations. [PPh₄]₂[(W₂Se₉)_0.66(W₂Se₁₀)_o.34] (P1, a = 10.556 (5) Å, b = 11.480 (6) Å, c = 22.324 (11) Å, α = 76.90 (2)°, β = 86.58 (2)°, γ = 79.28 (2)°, Z = 2) and [PPh₄]₂[W₂Se₁₀] (asymmetric/symmetric isomer ratio 0.73/0.27, P1, a = 10.678 (2) Å, b = 11.492 (3) Å, c = 22.392 (5) Å, α = 77.20 (2)°, β = 86.94 (2)°, γ = 79.81 (2)°, Z = 2) crystallize from these mixtures and have in common the (W₂(μ-Se)₂Se₂)^2- core. W₂Se^2-₉ and the two isomeric W₂Se^2-₁₀ anions differ only in the chain lengths of the chelating polyselenides. In these structures the WSe₃ and WSe₄ rings have conformations similar to cyclobutane and cyclopentane, respectively. Detailed structural data are reported. The ⁷⁷Se NMR data for the selenides in DMF solution are presented and indicate that the solid-state structures remain intact in solution.