Coordination of Halide and Chalcogenolate Anions to Heavier 1,2,5-Chalcogenadiazoles: Experiment and Theory

New products of coordination of anions X– (X = F, I, PhS) to the Te atom of 3,4-dicyano-1,2,5-telluradiazole (1) were synthesized in high yields and characterized by X-ray diffraction (XRD) as the salts [(Me2N)3S]+[1-F]− (9), [K(18-crown-6)]+[1-I]− (10), and [K(18-crown-6)]+[1-SPh]−·THF (11), respectively. In the crystal lattice of 10, I atoms are bridging between two Te atoms. The bonding situation in anions of the salts 9–11 and some other adducts of 1,2,5-chalcogenadiazoles (chalcogen = S, Se, Te) and anions X– (X = F, Cl, Br, I, PhS) was studied using DFT, QTAIM, and NBO calculations, for 9–11 in combination with UV–vis, IR/Raman, and MS-ESI techniques. In all cases, the nature of the coordinate bond is negative hyperconjugation involving the transfer of electron density from X– to the heterocycles. The energy of the bonding interaction varies in a range from ∼30 kcal mol–1 comparable with energies of weak chemical bonds (e.g., internal N–N bond in organic azides) to ∼86 kcal mol–1 comparable with an ...