Charge-transfer interactions in the square-planar chalcogen cations, M42+: preparation and crystal structures of the compounds (Se42+)-(Sb2F42+)(Sb2F5+)(SbF6–)5, (Se42+)(AlCl4–)2, and (Te42+)(SbF6–)2

Abstract

The solid-state structures of the compounds (1)(Se₄²⁺)(Sb₂F₄²⁺)(Sb₂F₅⁺)(SbF₆^–)₅, (2)(Te₄²⁺)(SbF₆^–)₂, and (3)(Se₄²⁺)(AlCl₄^–)2 are reported. The first compound was initially isolated from the reaction of a 1:3 sulphurselenium alloy with a SbF₅–SO₂ solution and the second by the reaction of a mixture of tellurium and germanium, with a SbF₅–SO2 solution. They have also been prepared by the direct oxidation of Se and Te with SbF₅ in SO₂. Crystals of (1) are monoclinic, space group P2₁/c, with a= 15.739(3), b= 13.498(2), c= 17.040(4)Å, β= 92.26(2)°, and Z= 4. The dark red plates of (2) are triclinic, space group A, with a= 5.700(2), b= 16.252(6). c= 8.076(2)Å, α= 100.56(3), β= 102.67(3), γ= 97.47(3)°, and Z= 2. Compound (3) is orthorhombic, space group Pbam, with a= 13.245(3), b= 13.223(3), c= 9.266(2)Å, and Z= 4. The structures of compounds (1) and (2) have been solved by direct methods and compound (3) by a Patterson function. They were refined by least squares to final agreement indices of R= 0.052 (R′= 0.062). 0.051 (0.064), and 0.042 (0.046) for 3 634, 709, and 912 observed reflections respectively. In these three compounds, the approximately square-planar chalcogen cations Se₄²⁺ and Te₄²⁺ were found to have crystallographic inversion symmetry with average Se–Se and Te–Te distances of 2.260(4)(1), 2.688(3)(2), and 2.286(2)Å(3). These values are close to the distances observed in the other examples of these cations. The packing of these and other examples of the Ma₄²⁺ cations, the anion–cation charge-transfer interactions, and the stereochemistry of the fluorine contacts to the antimony(III) atoms in the Sb₂F₄²⁺ and Sb₂F₅⁺ ions and related species are discussed.