Simulated CTA-Anion Complexes at MP2 level

Data were generated using Gaussian 16, applying the ONIOM (Our own N-layered Integrated molecular orbital and molecular mechanics) approach with second-order Møller–Plesset perturbation theory (MP2) and the Polarizable Continuum Model (PCM) to simulate water as an implicit solvent. The geometries of cetyltrimethylammonium ion paired with bisulfate, nitrate, and methyl sulfonate anions were optimized. Vibrational frequencies and infrared spectra were then computed from both equilibrium and displaced geometries to account for the electrostatic screening effects associated with ion pairing.