Enhancing the interactions between neutral molecular tweezers and anions.

Several structural modifications to the original molecular tweezers of the Klärner's group were made with the aim of improving its binding capacity towards anions. The proposed modifications raise the molecular electrostatic potential inside the cavity and provide more conformational flexibility. The complexes of these new molecules with the halide anions Cl(-), Br(-), I(-) were optimized at the MPW1B95/6-31+G* level of theory. The molecular interactions were analyzed by single point density fitted local second-order Møller-Plesset perturbation theory (DF-LMP2) and DF-LMP2 spin-component-scaled MP2 (SCS-MP2), calculations were performed with the cc-pVTZ basis set. In view of the large magnitude of the interaction energies computed and the stability of the complexes in different solvents, this kind of molecule is a good candidate as molecular host for anion recognition.