Quantification and understanding of non-covalent interactions in molecular and ionic systems: Dispersion interactions and hydrogen bonding analysed by thermodynamic methods

Abstract

The attractive part of the van der Waals potential is commonly referred to as dispersion forces. Dispersion forces are a ubiquitous phenomenon with significant implications for chemistry, biochemistry, and materials science. Admittedly, the dispersion interactions are considered “weak”. For this reason, the quantification of the dispersion forces is rather challenging. In this paper we used the DFT methodology with def2-TZVPP basis set to evaluate dispersion interactions in molecular and ionic systems. We also quantify the dispersion contributions with help of the complementary to DFT experimental methods based on thermochemical quantities: standard molar vaporization enthalpy and the ideal-gas standard molar enthalpy of formation. We used a bunch of experimental thermodynamic methods (combustion calorimetry, solution calorimetry, differential scanning calorimetry, thermogravimetry, vapour pressure determination with combined Quartz Crystal Microbalance, Knudsen method, transpiration technique, static method) to quantify the dispersion forces in molecular and ionic systems. Experimental studies have been performed on the well-chosen sets of molecular compounds (alkanes, alcohols, amines, aromatics) and ionic liquids (ammonium and phosphonium based ionic liquids). The main idea was based on the predominant view that bulky groups in molecular structures are more likely considered repulsive rather than stabilizing. In view of the fact that a delicate balance between attraction and repulsion can be quantified and rationalized, the approach developed in this work can help establish new design principles based on the conscious inclusion of dispersion as an important stabilizing factor. The ensemble of experimental techniques and quantum chemical methods (DFT with D3 dispersion correction) enabled the development of quantitative scales of the dispersion contributions and their understanding at the molecular level.