Methylation strengthens π–π CO2 stacking with polymethylated imidazoles

High-level ab initio wavefunction methods such as MP2, CCSD and CCSD(T) have been used to study the complexes between imidazole and methyl-derivatives of imidazole with CO 2 , as methylated imidazole derivatives may be environmentally-friendly and efficient systems for capturing carbon dioxide. The two most stable arrangements correspond to a N···C tetrel bond and a configuration in which CO₂ lies above the π-cloud of the imidazole ring. Importantly, it has been found that methyl substitution modulates the relative stability of these minima, in contrast with the imidazole-CO₂ reference system. Polymethylation not only increases binding energies, but also allows the steric hindrance generated at the preferred binding site to be overcome by strengthening the π – π interactions, as reflected by SAPT-DFT. The study also provides microwave-range spectroscopic information, and Machine Learning methodologies have been applied to explore the potential energy surface.