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 SO 2 is presented. ILs used are ethylmethylimidazolium triflate [OTf] − and tetraalkylammonium triflylimide [NTf 2 ] − . Tristriflylmethanide [CTf 3 ] − was used as [BuMeIm][CTf 3 ] as the electrolyte in SO 2 . This allowed for the isolation of [Te 4 ][CTf 3 ] 2, [Te 6 ][OTf] 4 , and [Te 8 ][NTf 2 ] 2 containing the square [Te 4 ] 2+ , the prismatic [Te 6 ] 4+ , and the novel barrelane‐shaped [Te 8 ] 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 [Te 8 ] 2+ features only one broad signal at 2700 ppm. DFT calculations show that slight concerted displacements within the [Te 8 ] 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 .