Geometries, interaction energies and complexation free energies of 18-crown-6 with neutral molecules

Abstract

Although 18-crown-6 is renowned for its binding affinity to various metal and ammonium cations, the nature and strength of its binding with neutral guest molecules is relatively unexplored. Here we report a computational study of the host:guest geometries, interaction energies and Gibbs free energies of formation of 18-crown-6 with 49 neutral guest molecules in the gas phase, using the G4(MP2) composite method. Optimized geometries are in excellent agreement with those observed in crystals, with differences readily attributed to guest:guest interactions in the solid state. Host:guest interaction energies range from -13 to -103 kJ mol -1 , and the estimated Gibbs free energies of binding at 298 K correlate with the observation (or not) of the complexes in crystals. The electrostatic, dispersion, polarization and repulsion components of the interaction energy have also been estimated using the recently described CE-B3LYP model energies, providing insight into the binding nature between 18C6 and neutral molecules.

Measurement of Electric Fields Experienced by Urea Guest Molecules in the 18-Crown-6/Urea (1:5) Host–Guest Complex: An Experimental Reference Point for Electric-Field-Assisted Catalysis

“…Compared to other organic hosts, crown ether complexes usually have simpler structures in the solid state and exhibit less disorder and air-sensitivity, making them more amenable to the detailed experimental investigation of their geometric and electronic structure in the solid state. Although 18-crown-6 (18C6) is well known for its binding affinity to various metal and ammonium cations, the nature and strength of its binding with neutral guest molecules remain relatively unexplored . 18C6:(neutral molecule) complexes commonly occur as trimers in the solid state, with two guest molecules bound above and below the 18C6 macrocycle.…”

Current developments and trends in quantum crystallography

“…9) (Turner et al, 2015); (iv) the computation of quite accurate lattice energies for molecular crystals . The techniques currently available in CE have already found many applications in many hot topics of solid-state chemistry and physics: (supra)molecular recognition (Shi, Sobolev et al, 2015;Shi, Thomas et al, 2015;Dey, Bhandary et al, 2016;Shi et al, 2016Shi et al, , 2017Shi et al, , 2019Grosjean et al, 2021), polymorphism Thomas, Grosjean et al, 2019), effects of temperature and pressure on crystal structures (Eikeland, Thomsen et al, 2016, 2017Sussardi et al, 2023), and structure-property relationships (Thomas, Shi et al, 2017;Karothu et al, 2022).…”