Encapsulation of small gas molecules and rare gas atoms inside the octa acid cavitand

Abstract

The potential for gas storage (C2H2, C2H4, C2H6, CO2, CO, H2, N2, NO2, NO) molecules and rare gas (Rg) atoms (Hen–Xen, where n = 1, 2) within the recently synthesized octa acid (OA) moiety is assessed through density functional theory-based computations. It is shown that C2H2, C2H4, C2H6, N2, Kr, and Xe atoms/molecules bind with octa acid in a thermodynamically favorable way. Wiberg bond indices, non-covalent interaction indices, and energy decomposition analyses are used to explore the nature of the interaction between guest atoms and octa acid. The nature of the interaction in between either two guest atoms (in the cases of Rg atoms) or guest and cage atoms is mostly of non-covalent type in nature. An ab initio molecular dynamics simulation carried out at 50 and 298 K temperatures reveal that many of the studied systems particularly concerning polar and π electron cloud containing guest molecules show good dynamical stability at both temperature regimes. Except for the case of Ne-encapsulated octa acid, all other rare gases tend to get liberated from the host at room temperature although they remain inside the host at low temperature, thereby showing good dynamical stability of the Rg-encapsulated octa acid complexes up to 500 fs. In order to reaffirm the dynamical stability, Ne2@OA and CO@OA are studied at 50 and 298 K up to 600 fs as test cases.