Theoretical study on ion-pair recognition of M(+)X(-) (M = Li, Na, K and X = F, Cl, Br) by formylaminocalix[4]arene derivatives.

DFT calculations were reported for calix[4]arene derivatives [i.e., formylaminocalix[4]arene (1) and formylaminocalix[4]bis-crown-3 (2)] binding cations M(+) (Li(+), Na(+), and K(+)) and anions X(-) (F(-), Cl(-), and Br(-)) simultaneously. The B3LYP function together with the LANL2DZp basis set was used in order to obtain insights into the factors determining the nature of the interactions of these compounds with X(-) and M(+). Based on the molecular electrostatic potential (MEP) analysis, the result complexes M(+)X(-)/H (H = 1, 2) were investigated. For all the complex structures, the most pronounced changes in geometric parameters upon interaction were observed in the host segment compared with the free receptors. Two main types of driving force, N-H∙∙∙X(-) hydrogen bonds and electrostatic interactions between M(+) and oxygen atoms, were confirmed. The recognition trends for 1 and 2 toward M(+)X(-) followed the same order: M(+)F(-) > M(+)Cl(-) > M(+)Br(-) (M(+) is same to each other) and Li(+)X(-) > Na(+)X(-) > K(+)X(-) (X(-) is same to each other). The binding energy, enthalpy change, Gibbs free energy change, and entropy change of complexation formation have been studied by the calculated thermodynamic data. In all cases, the inclusion energy changes with 2 were more negative than those with 1, correlating with the flexible space available by the two crown ether moieties in 2. The calculated results of the model system have been reported and should be useful to the experimental research in this field.