A matrix isolation and Ab initio study on C2H6••HCN complex: An unusual example of hydrogen bonding

Hydrogen bonding between saturated alkanes and HX (X is an electronegative fragment) represents a unique type of interaction of this kind. In this work we report a first experimental and ab initio study on HCN center dot center dot center dot C2H6 complex using FTIR matrix isolation spectroscopy and MP2/CBS calculations. According to theoretical results, three forms of HCN...C2H6 are possible: two with C(HCN)...C1(C2H6) and H(HCN)center dot center dot center dot C-2(C2H6); C(HCN)...C1(C2H6) and N(HCN)...C-2(C2H6) contacts and hydrogen-bonded H(HCN)...C(C2H6) axial symmetry structure (the interaction energies are 0.85, 0.79 and 0.77 kcal/mol respectively). Nevertheless, only the last structure is stabilized upon experimental conditions. The hydrogen-bonded complex is spectroscopically characterized by blue shifts of HCN bending (+ 9.4 cm(-1)) and CH3 rocking ( + 9.0 and + 11.3 cm(-1)) and red shifts of H -CN stretching (-24.9 and -20.1 cm(-1)) and CH3 symmetry stretching (-4.7 cm(-1) ) vibrations. The experiment with deuterated HCN proves this assignment. The obtained results are in good agreement with the previous rotational spectroscopy study. (C) 2021 Elsevier B.V. All rights reserved.