The reaction of 2,3‐diaminomaleonitrile with TeX4 (X = Cl, Br) in the presence of pyridine (Py) and/or triethylamine (Et3N) provided 3,4‐dicyano‐1,2,5‐telluradiazole (1), which was isolated neat and as stable adducts with pyridine, chloride, and bromide, namely, 1·2Py, (PyH)(1·Cl), (PyH)2(1·2Cl), (Et3NH)(1·Cl), (PyH)(1·Br), and (PyH)2(1·2Br). The molecular and supramolecular structures of these compounds were investigated by X‐ray crystallography. In the solid state, intermolecular associations through secondary Te···N interactions as well as N–H···X and N–H···N hydrogen bonding (X = Cl, Br) were observed. For (PyH)(1·Br), two polymorphs were found. The bonding situation of 1 and its pyridine and chloride adducts were investigated by MP2 calculations supplemented with the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. The π symmetry of the frontier molecular orbitals (MOs) of 1 are preserved in the 1·2Py, (1·Cl–), and (1·2Cl–) adducts. In the chloride adducts, the highest occupied molecular orbital (HOMO) can be described as an antibonding combination of the HOMO of 1 with the 3p atomic orbitals (AOs) of the chloride ions, whereas the lowest occupied molecular orbital (LUMO) resembles that of the parent 1. The charge transfer onto the heterocycle in the adducts increases in the order 1·2Py, (1·2Cl–), and (1·Cl–). QTAIM analyses of the adducts in the gas phase reveal closed‐shell interactions, whereas NBO analyses indicate negative hyperconjugation as the main formation pathway in these complexes. This description agrees with the Alcock model suggested for secondary bonding interactions between atoms of heavy p‐block elements and atoms with lone pairs.

The nitroxides of 7-azadispiro[5.1.5.2]pentadecane and 7-azadispiro[5.1.5.2]pentadeca-14-ene series have been prepared, including thiol-specific methane thiosulfonate spin label for site-directed spin labeling. The effect of spirocyclohexane moieties on chemical and spectral properties has been studied. The obtained temperature dependencies of electron spin relaxation parameters demonstrate that new nitroxides may be suitable for PELDOR distance measurements at 80-120 K. Moreover, the new nitroxides demonstrated much higher stability toward reduction by ascorbate than spirocyclohexane-substituted nitroxides of piperidine series and showed 1.3-3.14 times lower reduction rates compared to corresponding 2,2,5,5-tetramethyl nitroxides.

According to the DFT calculations, [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (4), [1,2,5]selenadiazolo[3,4-c][1,2,5]thiadiazole (5), 3,4-dicyano-1,2,5-thiadiazole (6), and 3,4-dicyano-1,2,5-selenadiazole (7) have nearly the same positive electron affinity (EA). Under the CV conditions they readily produce long-lived π-delocalized radical anions (π-RAs) characterized by EPR. Whereas 4 and 5 were chemically reduced into the π-RAs with thiophenolate (PhS(-)), 6 did not react and 7 formed a product of hypercoordination at the Se center (9) isolated in the form of the thermally stable salt [K(18-crown-6)][9] (10). The latter type of reactivity has never been observed previously for any 1,2,5-chalcogenadiazole derivatives. The X-ray structure of salt 10 revealed that the Se-S distance in the anion 9 (2.722 Å) is ca. 0.5 Å longer than the sum of the covalent radii of these atoms but ca. 1 Å shorter than the sum of their van der Waals radii. According to the QTAIM and NBO analysis, the Se-S bond in 9 can be considered a donor-acceptor bond whose formation leads to transfer of ca. 40% of negative charge from PhS(-) onto the heterocycle. For various PhS(-)/1,2,5-chalcogenadiazole reaction systems, thermodynamics and kinetics were theoretically studied to rationalize the interchalcogen hypercoordination vs reduction to π-RA dichotomy. It is predicted that interaction between PhS(-) and 3,4-dicyano-1,2,5-telluradiazole (12), whose EA slightly exceeds that of 6 and 7, will lead to hypercoordinate anion (17) with the interchalcogen Te-S bond being stronger than the Se-S bond observed in anion 9.

A simple method for the synthesis of sterically shielded pyrrolidine nitroxides, including the title compound, has been suggested. The key procedure implies assembling the pyrrolidine ring from α-amino acid, ketone, and activated alkene in a three-component domino process, followed by oxidation to nitrone and Grignard reagent addition. The new nitroxides demonstrate very high stability against reduction with ascorbate.