Impact of ligands on CO2 adsorption in metal-organic frameworks: First principles study of the interaction of CO2 with functionalized benzenes. II. Effect of polar and acidic substituents

Abstract

Intermolecular interactions between the CO2 molecule and a range of functionalized aromatic molecules have been investigated using density functional theory. The work is directed toward the design of linker molecules which could form part of new metal-organic framework materials with enhanced affinity for CO2 adsorption at low pressure. Here, the focus was on the effect of introducing polar side groups, and therefore functionalized benzenes containing NO2, NH2, OH, SO3H, and COOH substituents were considered. The strongest types of intermolecular interactions were found to be: (i) between lone pair donating atoms (N,O) of the side groups and the C of CO2 (enhancement in binding energy of up to 8 kJ mol−1 compared to benzene); and (ii) hydrogen bond interactions between acidic protons (of COOH and SO3H groups) and CO2 oxygen (enhancement of 3–4 kJ mol−1). Both of these types of interaction have the effect of polarizing the CO2 molecule. Weaker types of binding include hydrogen-bond-like interactions with aromatic H and π-quadrupole interactions. The strongest binding is found when more than one interaction occurs simultaneously, as in C6H5SO3H and C6H5COOH, where simultaneous lone pair donation and H-bonding result in binding energy enhancements of 10 and 11 kJ mol−1, respectively