Theoretical Investigation of the Structures and Energetics of (MX)-Ethanol Complexes in the Gas Phase

The structures and energy of alkali halide salt (MX) complexes with ethanol have been investigated in this work. The core of this study is to explore the effect of ion size on the interactions between solvent and solute. LiF and KBr as monovalent salts with different sizes of inion and cation have been chosen to explore this difference in addition to various physical properties. Three complexes of each LiF and KBr with ethanol taking the formula MX(CH3CH2OH)n (n=1-3), were studied. Ab-initio calculations have been performed to optimize the chemical structures of these complexes and explore the possible structures, isomers, and their corresponding IR spectra using Density functional theory (DFT/ B3LYP). 6-311G** were chosen as basis sets for these calculations. The geometry evaluations, energy searches, vibrational frequency calculations, and each complex's binding energy were also theoretically extracted in this study. The minimum energy structures were calculated, and different isomers were found. The presence of Ionic hydrogen bonds (IHBs) was observed and proposed to be the main binding between the MX salt and ethanol. Also, the infrared vibrational bands in the OH stretching region were recorded for the minimum structures, and the determined red-shift was at about 400 cm-1. In addition, the binding energy calculations found a gradual rise in the BE value with every additional ethanol molecule added to MX salt.