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 CH 3 - and NH 2 -substituted ones, in which the largest stability belongs to the complexes involving NH 2 -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 t he 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.