The Electrochemical Synthesis of Polycationic Clusters.

As a new method for the synthesis of chalcogen polycationic clusters, the electrochemical dissolution of elemental tellurium in ionic liquids (IL) or in liquid SO2 is presented. ILs used are ethylmethylimidazolium triflate [OTf](-) and tetraalkylammonium triflylimide [NTf2](-). Tristriflylmethanide [CTf3](-) was used as [BuMeIm][CTf3] as the electrolyte in SO2. This allowed for the isolation of [Te4][CTf3]2, [Te6][OTf]4, and [Te8][NTf2]2 containing the square [Te4](2+), the prismatic [Te6](4+), and the novel barrelane-shaped [Te8](2+). The compounds are novel compositions as they do not contain the usual halometalate anions, but rather common weakly coordinating anions. The (125)Te NMR spectrum of an IL solution containing [Te8](2+) features only one broad signal at 2700 ppm. DFT calculations show that slight concerted displacements within the [Te8](2+) cluster lead to a fluxional molecular structure and a fast valence isomerism with a very low activation barrier of about 8 kJ mol(-1).