The Csp2-H...O/Se/Te and O-H...Se/Te nonconventional hydrogen bonds in the systems of formic acid with selenoformaldehydes and telluroformaldehydes

Abstract

This study conducts a thorough investigation into the stability of complexes as well as the hydrogen bonds along with their characteristics in the systems between formic acid and chalcoaldehyde derivatives. Generally, the strength of complexes is enhanced irrespective of electron donating or withdrawing substitution in chalcoaldehyde derivatives. It is found that the complexes involving Se-substitution are slightly more stable than Te-one. The halogenated complexes are less stable than CH₃- and NH₂-substituted ones, in which the largest stability belongs to the complexes involving NH₂-substituted group. The obtained results show a dominant role of O–H∙∙∙Se/Te compared to C–H∙∙∙O in contributing to the stabilization of complexes. Calculated results indicate that the strength of nonconventional hydrogen bonds decreases in the order of O–H∙∙∙Se > O–H∙∙∙ Te ~ C–H∙∙∙O > C–H∙∙∙Se/Te. The larger blue shift of C-H bond in the complexes investigated is observed in C–H∙∙∙O compared to C–H∙∙∙Se/Te. The magnitude of blue shift is larger in the case of C–H∙∙∙Se than in C–H∙∙∙Te hydrogen bonds. NBO analysis shows that the blue-shifted stretching frequency of C_sp2–H depends mainly on a reduction of electron density at σ*(C_sp2–H) orbital. The redshift in O-H∙∙∙Se/Te hydrogen bonds in these systems is determined by a considerable increase of electron density at σ*(O–H) orbitals, overcoming an s-character enhancement of the O site upon complexation.