In search of OH–π interactions between 1-methylimidazole and water using a combined computational quantum chemistry and ATR-FTIR spectroscopy approach

To determine if OH–π interactions occur between 1-methylimidazole (1-MI) and water, the density functional theory methods (DFT) B3LYP and M05-2X, and the ab initio MP2 method calculated the vibrational frequencies and energies of explicitly hydrated models of 1-MI. The comparison of the B3LYP/6-311++G(d,p) energy-minimized frequencies for the 1-MI·2H2O model showed better correlation with the aqueous-phase ATR-FTIR data than the results obtained with the M05-2X and MP2 methods for levels with other amounts of hydration. Moreover, the 1-MI·2H2O showed no evidence for OH–π interactions but showed evidence for HO–H⋯N H-bonds. However, the 1-MI·4H2O and 1-MI·8H2O models, energy minimized with M05-2X and MP2 showed evidence for OH–π interactions. Systematic energy re-minimization calculations for all of the hydrated 1-MI models indicated that the M05-2X and MP2 methods predicted structures that were less thermodynamically favorable than those calculated using B3LYP. These results suggest that M05-2X and MP2 are erroneously predicting OH–π interactions, while B3LYP is predicting structures with HO–H⋯N H-bonds that are consistent with the experimental data.