Radical Anions, Radical-Anion Salts and Anionic Complexes of 2,1,3-Benzochalcogenadiazoles (S, Se, Te).

With cyclic voltammetry (CV) and DFT calculations, it was found that electron acceptor ability of the 2,1,3-benzochalcogenadiazoles 1-3 (chalcogen: S, Se and Te, respectively) increases with the atomic number of chalcogen. This trend is nontrivial since it contradicts the electronegativity and atomic electron affinity of the chalcogens. In contrast to radical anions (RAs) [1]*- and [2]*-, RA [3]*- was not detected by EPR under the CV conditions. Chemical reduction of 1-3 was performed and new thermally-stable RA salts [K(THF)]+[2]*- (8) and [K(18-crown-6)]+[2]*- (9) were isolated in addition to known salt [K(THF)]+[1]*- (7). Upon contact with air, RAs [1]*- and [2]*- underwent fast decomposition in solution with the formation of anions [ECN]- isolated in the form of salts [K(18-crown-6)]+[ECN]- (10, E = S; 11, E = Se). In the case of 3, RA [3]*- was detected by EPR to be the first representative of tellurium-nitrogen π-heterocyclic RAs but not isolated. Instead, salt [K(18-crown-6)]+2[3-Te2]2- (12) featuring a new anionic complex with the coordinate bond Te-Te was obtained. Upon contact with air, salt 12 transformed into salt [K(18-crown-6)]+2[3-Te4-3]2- (13) revealing an anionic complex with two coordinate bonds Te-Te. The structures of 8-13 were confirmed by X-ray diffraction and the nature of the coordinate bonds Te-Te in [3-Te2]2- and [3-Te4-3]2- was studied with DFT calculations and QTAIM analysis.