Ab initio and DFT investigations of lithium/hydrogen bonded complexes of trimethylamine, dimethyl ether and dimethyl sulfide

Abstract

Ab initio and DFT computations have been carried out on LiF and HF complexes of a set of n-donors viz. trimethylamine, dimethyl ether and dimethyl sulfide with a 6-31++G(d,p) basis set. The effect of correlation has been included with MP2, MP4 and DFT calculations. NBO analyses of the wavefunctions have been performed to examine the intermolecular interaction at the orbital level. Calculations reveal that these donors form strong n→σ* complexes and computed binding energies of the (CH3)2O···HF complex agree very well with the experimental binding energies from IR spectroscopy. LiF forms stronger complexes than HF, and the effect of correlation on the hydrogen bond energy is considerable compared to the lithium bond energy. Though charge transfer interaction contributes to the stability of both LiF and HF complexes, it plays a less dominant role in lithium bonded complexes. While amine and ether donate their nσ lone pair, sulfide donates an nπ lone pair and this results in perpendicular intermolecular bonds in sulfide complexes.