Substituent effects on the coordination of benzo-21-crown-7 and dibenzo-21-crown-7 with cesium: Insights from computational chemistry and nuclear magnetic resonance spectroscopy

Abstract

Aromatic substituent plays a pivotal role in determining the electronic characteristics and coordination capabilities of aromatic crown ethers (CE). In this study, we focus on two types of aromatic CEs: benzo-21-crown-7 (B21C7) and dibenzo-21-crown-7 (DB21C7). Employing isochemical shielding surface (ICSSZZ) analysis for the first time, we investigate their aromaticity. The thermodynamic properties of their complexes with cesium are calculated using the double-hybrid functional PWPB95-D3, incorporating precise dispersion description. Interactions and conformations are examined through 1D and 2D NMR methods, and coordination dynamics are elucidated via molecular dynamics (MD) simulations. The ESP extreme value of B21C7 is lower than that of DB21C7, indicating stronger electrostatic attraction with Cs+. Solvent effects exert adverse influences on thermodynamic stability, leading to decreased binding Gibbs free energy (|ΔG|) and coordination number (CN) in chloroform compared to the gas phase. Interestingly, the stability of Cs+·B21C7 decreases more than that of Cs+·DB21C7. From a dynamic perspective, an increase in the number of aromatic substituents enhances the structural rigidity of the cavity, facilitating the formation of Cs+·DB21C7. This study establishes a connection between substituent and coordination, offering valuable insights for developing aromatic CEs with high-affinity binding capabilities for metal cations.