Complexation mechanism of crown ethers with rubidium and cesium ions using density functional theory

Abstract

The complexation mechanism of crown ether derivatives (18C6, 21C7, B18C6, B21C7) with metal ions (Li+, K+, Rb+, Cs+) has been studied. Structural optimization was performed at the level of M06-2X/def2SVP. The results show that M+ mainly interacts with oxygen atoms, and CO bonds become longer after complexation. The interactions belong to the electrostatic attractive effect. The electrophilic substitution activity of crown ethers can be improved by benzene ring substituents, while the electrophilic complexing reaction activity decreases. 21C7 has the lowest electrostatic potential minimum, which is −96.0 kcal·mol−1. The complex 21C7-Cs+ and 21C7-Rb+ are more stable than other 21C7 complexes. The binding energy and Gibbs free energy of 21C7-Cs+ are −66.6 and −66.0 kcal·mol−1, respectively. The results can provide theoretical guidance for the design of crown ethers using for the extraction of Rb+ and Cs+ from brines.