Fundamental insights into the structural characteristic of dihydrogen-bonded complexes of C2H4−nCln⋯MgH2 (n = 0, 1, 2, 3)

Abstract

At the MP2 computational method level, a systematic investigation has been conducted on the dihydrogen-bonded complexes formed by ethylene, its chlorine derivatives, and magnesium hydride. According to the optimized structures, the complexes under study are classified into three groups. The most stable among them are circular structures stabilized by CH⋯H and HMg⋯Cl bonds, with interaction energies ranging from 3.4 to 5.9 kcal mol⁻¹. The other group consists of linear structures, which are only stabilized by CH⋯H dihydrogen bonds and have relatively lower interaction energies between 0.5 and 2.0 kcal mol⁻¹. For all the investigated complexes, a slight elongation of the C–H bond is observed, accompanied by a red shift in its stretching frequency. As the number of chlorine atoms on the ethylene molecule increases, the geometries, frequencies, interaction energies of the complexes, and the electron density in the σ* antibonding orbital of C–H all show a gradual increase or decrease. Through atoms in molecules (AIM) and natural bond orbital (NBO) analyses, the nature of the electrostatic interaction in this type of dihydrogen bond has been revealed. By comparing the geometric data and AIM parameters, the effect of ring structures on dihydrogen bonding systems has been evaluated. Notably, the direction of net charge transfer in ring structure complexes is opposite to that previously observed in dihydrogen-bonded systems.