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 ¹²⁵Te 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.