Novel long-lived π-heterocyclic radical anion:a hybrid of 1,2,5-thiadiazo- and 1,2,3-dithiazolidyls

A long-lived π-heterocyclic radical anion of the hybrid 1,2,5-thiadiazolidyl / 1,2,3-dithiazolidyl type was electrochemically generated and characterized by EPR spectroscopy and DFT calculations

Novel long-lived π-heterocyclic radical anion:a hybrid of 1,2,5-thiadiazo- and 1,2,3-dithiazolidyls

A long-lived π-heterocyclic radical anion of the hybrid 1,2,5-thiadiazolidyl / 1,2,3-dithiazolidyl type was electrochemically generated and characterized by EPR spectroscopy and DFT calculations

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

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

Radical anions, radical-anion salts, and anionic complexes of 2,1,3-benzochalcogenadiazoles

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

Acid-base and anion binding properties of tetrafluorinated 1,3-benzodiazole, 1,2,3-benzotriazole and 2,1,3-benzoselenadiazole

The influence of fluorination on the acid-base properties and the capacity of structurally related 6-5 bicyclic compounds – 1,3-benzodiazole 1, 1,2,3-benzotriazole 2 and 2,1,3-benzoselenadiazole 3 to σ-hole interactions, i.e. hydrogen (1 and 2) and chalcogen (3) bondings, is studied experimentally and computationally. The tetrafluorination increases Brønsted acidity of diazole and triazole scaffolds and Lewis acidity of selenadiazole scaffold and decreases basicity. Increased Brønsted acidity facilitates anion binding via the formation of hydrogen bonds; particularly, tetrafluorinated derivative of 1 (compound 4) binds Cl–. Increased Lewis acidity of tetrafluorinated derivative of 3 (compound 10), however, is not enough for binding with Cl– and F– via the formation of chalcogen bonds in contrast to previously studied Te analog of 10. It is suggested that the maximum positive values of molecular electrostatic potential at the σ-holes, VS,max, can be reasonable metrics in the further design and synthesis of new anion receptors, with selenadiazole–diazole / triazole hybrids as a special target. Related chlorinated compounds are also discussed. Introduction Design and synthesis of new anion receptors functioning via various σ-hole interactions,[1] e.g. hydrogen and chalcogen bondings (Brønsted and Lewis acidity, respectively), attract much current attention, particularly due to potential biomedical, technological and environmental applications.[2-4] Effective tool in the field is polyfluorination, for (hetero) aromatics affecting many properties significant for chemistry, materials science and biomedicine, including a capacity to σ-hole interactions.[1,5-9] Structurally-related, 1,2-diaminobenzene-derived, 1,3- benzodiazole (benzimidazole) 1, 1,2,3-benzotriazole 2, and 2,1,3-benzoselenadiazole 3, already having numerous applications in current chemistry, materials science and biomedicine,[7,10] are appropriate targets for studying effects of polyfluorination on Brønsted (1 and 2) and Lewis (3) acidity and anion-binding properties (Scheme 1)