Theoretical Study on the Nature and Cooperation of C-H•••O and C-H•••π Interactions in the Pillar [5]arene and n-Alkanes Complexes

Using the calculation result of the binding energy of the CCSD (T)/CBS method as the standard, the CAM-B3LYP-D3BJ/def2-SVPD density functional theory (DFT) method was chosed to calculate the binding energy of the MeP5 center dot center dot center dot CnH2n+2 (n=1-10, 12, 14, 16) complexes. The results show that there is a strong interaction between the host and guest, and the binding energy increases with the growth of the alkane carbon chain. The Gibbs free energy and enthalpy change are both less than zero at standard conditions (nominally 298.15 K, 101325 Pa) , which indicating that the formation of the complexes is spontaneous, and the main driving force associated with is enthalpy. The nature and cooperation of the C-H center dot center dot center dot pi and C-H center dot center dot center dot O interactions between alkanes and dimethoxypillar [5] arene (MeP5) were explored using the absolutely localized molecular orbitals energy decomposition analysis (ALMO-EDA) method, and found that the sum of the electrostatic and dispersion effects accounts for about 94% of the total attraction, and their contribution is similar, with polarization and charge transfer accounting for only 6%.