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 [(Me ₂N)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 energy of the C-C covalent bonds. The thermodynamics of the anions' coordination to 1 and their Se and S congeners was also studied by quantum chemical calculations. The general character of this reaction and favorable thermodynamics in the case of heavier chalcogens (Se, Te) were established. Comparison with available data on acyclic analogues, i.e. the chalcogen diimines RN-X-NR, reveals that they also coordinate various anions but in addition reactions across X-N (X = S, Se, Te) double bonds. Attempts to prepare the anion [1-TePh]^- led to disintegration of 1. The only unambiguously identified product was a rather rare tellurocyanate that was characterized by XRD and elemental analysis as the salt [K(18-crown-6)]⁺[TeCN]^- (13).