Radical Anions, Radical‐Anion Salts, and Anionic Complexes of 2,1,3‐Benzochalcogenadiazoles

• Published in: Chemistry : a European journal 2019-01, Vol.25 (3), p.806-816
• Main Authors: Pushkarevsky, Nikolay A., Chulanova, Elena A., Shundrin, Leonid A., Smolentsev, Anton I., Salnikov, Georgy E., Pritchina, Elena A., Genaev, Alexander M., Irtegova, Irina G., Bagryanskaya, Irina Yu, Konchenko, Sergey N., Gritsan, Nina P., Beckmann, Jens, Zibarev, Andrey V.
• Format: Article
• Language: English
• Subjects: Anions; Atomic properties; chalcogens; Chemical reduction; Chemistry; density functional calculations; Electron affinity; Electronegativity; heterocycles; main group elements; Mathematical analysis; Organic chemistry; radical ions; Salts; Spectroscopy; Spectrum analysis; Tellurium; Thermal stability
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201803465

By means of cyclic voltammetry (CV) and DFT calculations, it was found that the electron‐acceptor ability of 2,1,3‐benzochalcogenadiazoles 1–3 (chalcogen: S, Se, and Te, respectively) increases with increasing atomic number of the 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 spectroscopy under 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). On contact with air, RAs [1].− and [2].− underwent fast decomposition in solution with the formation of anions [ECN]−, which were 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 spectroscopy as 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 coordinate Te−Te bond was obtained. On contact with air, salt 12 transformed into salt [K(18‐crown‐6)]+2[3‐Te4‐3]2− (13) containing an anionic complex with two coordinate Te−Te bonds. The structures of 8–13 were confirmed by XRD, and the nature of the Te−Te coordinate bond in [3‐Te2]2− and [3‐Te4‐3]2− was studied by DFT calculations and QTAIM analysis. Heterocyclic radical anions: Chemical reduction of 2,1,3‐benzochalcogenadiazoles 1–3 (chalcogen=S, Se, Te, respectively) afforded new thermally stable radical anion (RA) salts [K(THF)]+[2].− and [K(18‐crown‐6)]+[2].− in addition to known salt [K(THF)]+[1].−, whereas RA [3].− was detected by EPR as the first Te–N π‐heterocyclic RA but not isolated; instead, salt [K(18‐crown‐6)]+2[3‐Te2]2− (12) featuring a new anionic complex with coordinate Te−Te bond was obtained (see figure).