SPECTROSCOPY STUDY OF MCl2(H2O)n CLUSTER USING AB INITIO CALCULATIONS

Abstract

The Infrared (IR) spectroscopy of alkali earth halide salt (MX2) complexes with few numbers of water molecules have been investigated for the first time in this work. BeCl2 and MgCl2 are divalent salts and have been incorporated with water as a polar solvent to form complexes of type MX2(H2O)n. The effect of ion size plays a critical rule in the interactions between solvent and solute. Therefore, Beryllium and Magnesium salts with chloride were chosen to explore this difference. The importance of BeCl2 and MgCl2 comes from their several applications in the industry and pharmacy. For instance, BeCl2 is widely used in the industry as a catalysis of Friede-Craft reactions, while the main application of MgCl2 in pharmacy is as hemodialysis and peritoneal dialysis fluids. Three complexes of each BeCl2 and MgCl2 with water, MX2(H2O)n (n=1-3), were studied, and the chemical structures of these complexes have been performed using ab initio calculations. Ab initio calculations were used to predict possible structures, isomers, and their corresponding IR spectra using Second-order Møller-Plesset perturbation theory (MP2) with 6-311++G as a basis sets. The Geometry evaluations, energy searches, vibrational frequency calculations, and the binding energy of each complex were also extracted theoretically. The minimum energy of complexes structures was calculated, and different isomers have been recorded. Ionic hydrogen bonds (IHBs) between the OH in each water molecule and the chloride ion in the MCl2 was proposed to be the main prevalent contribution to the binding between the salt and water. The bond length between the alkaline metal and chlorine showed a significant increase with increasing the attached water molecule as a result of forming the IHB. Also, the infrared vibrational bands of the OH stretching region were recorded for the minimum structures, and dramatic redshift was performed. The formation of contact-ion pair structures in which each solvent molecule forms an ionic hydrogen bond (IHB) to the salt ion-pair (X-M+X-) has been confirmed by the predicted infrared spectra.