Dynamic and static behaviors of N-Z-N σ(3c-4e) (Z = S, Se, and Te) interactions: Atoms-in-molecules dual functional analysis with high-resolution X-ray diffraction determination of electron densities for 2-(2-pyridylimino)-2 H -1,2,4-thiadiazolo[2,3- a]pyridine

摘要

The structure of 2-(2-pyridylimino)-2H-1,2,4-thiadiazolo[2,3-a]pyridine (NSN) indicates that the molecule has a planar geometry with a linear N?S?N linkage, creating a tetracyclic structure of the formal C_(2v) symmetry. To clarify the nature of the NSN σ(3c-4e) bonding, together with the related NSeN and NTeN, the dynamic and static behaviors are investigated by applying atoms-in-molecules (AIM) dual functional analysis to both the fully optimized and perturbed structures. The structures were optimized computationally, retaining C_(2v) symmetry. All bond critical points are detected as expected and exhibited on both sides of the N?Z?N moiety which supports the formation of NZN σ(3c-4e). It is confirmed that N?S?N is of the covalent nature close to Me_2S~+-*-Cl or Me_2Se~+-*- Br, whereas N?Se?N and N?Te?N have the (regular) CS nature close to the CT adducts of Me_2S(-*-Cl)_2 (TBP) and Me_2Se-*-Br_2 (MC), respectively. An experimental high-resolution charge density determination has been performed on NSN, which thoroughly supports the theoretical results. Very similar results are obtained in the analogous pyrimidyl derivatives for N?S?N, N?Se?N, and N?Te?N. AIM dual functional analysis, as validated by experimental high-resolution charge densities, is thus confirmed to be an excellent method to elucidate the nature of these interactions.