Journal of Physical Chemistry A, Vol.115, No.42, 11775-11787, 2011
Dynamic and Static Behaviors of N-Z-N sigma(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)-2H-1,2,4-thiadiazolo[2,3-a]pyridine
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 center dot center dot center dot S center dot center dot center dot N linkage, creating a tetracyclic structure of the formal C(2v) symmetry. To clarify the nature of the NSN sigma(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 center dot center dot center dot Z center dot center dot center dot N moiety which supports the formation of NZN sigma(3c-4e). It is confirmed that N center dot center dot center dot S center dot center dot center dot N is of the covalent nature close to Me(2)S(+)-(*)-Cl or Me(2)Se(+)-(*)-Br, whereas N N center dot center dot center dot S center dot center dot center dot N is of the covalent nature close to Me(2)S(+)-(*)-CL or Me(2)Se(+)-(*)-Br, whereas N center dot center dot center dot Se center dot center dot center dot N and N center dot center dot center dot Te center dot center dot center dot N have the (regular) CS nature close to the CT adducts of Me(2)S(-(*)-Cl)(2) (TBP) and Me(2)Se-(*)-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 center dot center dot center dot S center dot center dot center dot N, N center dot center dot center dot Se center dot center dot center dot N, and N center dot center dot center dot Te center dot center dot center dot 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.