Oxotrihalogenoselenate(IV): Darstellung, Struktur und Eigenschaften von P(C6H5)4SeOCl3, P(C6H5)4SeOBr3 und As(C6H5)4SeOBr3

Abstract
The novel oxotribromosolcnate(IV) SeOBr3- anion was prepared from the reaction of stoichiometric quantities of SeOBr2 and bromide in acetonitrile solution, and it was isolated as the tetraphenylphosphonium and -arsonium salts in crystalline form. For the synthesis of the analogous SeOCl3- as P(C6H5)4SeOCl3, SeCl4 was reacted in the presence of a small quantity of H2O with P(C6H5)4Cl in acetonitrile. Complete X-ray structural analyses of P(C6H5)4SeOCl3 (space group P1̄, a = 10.981(3), b = 11.0511(3), c = 10.358(3) Å, α = 73.77(2)°, β = 83.33(2)°, γ = 80.51(2)°, V = 1187.9(6) Å3) and of P(C6H5)4SeOBr3 (space group P 21/c, a = 11.719(4), b = 16.088(4), c = 13.124(4) Å, β = 94.72(3)°, V = 2400(1) Å3) show dimeric centrosymmetric Se2O2Cl6 2- and Se2O2Br6 2- anions being present in the solid. In the anions two square-pyramidal (Ψ-octahedral) SeOHal4 groups are connected through a common Hal-Hal edge. The axial oxygen ligands (So-O: 1.597(4) and 1.584(0) Å) cause a pronounced stereochemical trans-activation of the inert pairs at the Se atoms. As(C6H5)4SeOBr3 is isotypic with P(C6H5)4SeOCl3.

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