FINDING OUT THE NONCONVENTIONAL C–H∙∙∙C HYDROGEN BOND IN THE COMPLEXES OF HALOFORMS WITH CARBON MONOCHALCOGENIDES

Abstract

The nonconventional C–H∙∙∙C hydrogen bonds were discovered and studied in detail in the interaction
between CHX3 (X = F, Cl, Br) and CZ (Z = O, S, Se, Te). The stability of the complexes and C–H∙∙∙C
hydrogen bonds increased along with the rise in proton donor ability of CHX3 and proton affinity at the C
atom of CZ. The C–H∙∙∙C hydrogen bonds in most complexes were red-shifting hydrogen bonds, with
decreasing magnitude in the C-H stretching vibrational frequency reaching 125.7 cm-1, except for the blue
shifting hydrogen bond observed in CHX3∙∙∙CO complexes with an increase in the C-H stretching vibrational
frequency up to 23.3 cm-1. It was noteworthy that the C-H blue-shift in C-H∙∙∙C was in general stronger than
C-H∙∙∙N, but weaker than C-H∙∙∙O. Notably, upon complexation, the C-H stretching vibrational frequency
tended to turn from blue-shift to red-shift as X changes from F to Br, and Z went sequentially from O to S, to
Se, and then Te. SAPT2+ analysis showed that the stability of the CHX3∙∙∙CZ complexes was mainly
contributed by the electrostatic component, which was more dominant than the induction and dispersion
ones.