theoretical study on steric effects, electronic properties, preorganization and solvent effect in host–guest chemistry of hexaprotonated form of an azacyclophane and halide anions

A theoretical study on the selectivity of hexaprotonated form of preorganized azacyclophane c3-trenphen (h6 l 6+) for halide anions in the gas phase and solution is reported. the calculated formation and interaction energies show the following trend: [f⊂h6 l]5+ > [cl⊂h6 l]5+ > [br⊂h6 l]5+ > [i⊂h6 l]5+. our calculations in both the gas phase and solution, in agreement with the experimental observations, show that the h6 l 6+ host has the largest selectivity for fluoride anion. indeed, the stronger host–guest interaction in [f⊂h6 l]5+ complex effectively compensates the unfavourable strain energy of the host and desolvation energy of fluoride anion. furthermore, herein, the solvent effect does not change the observed trend for gas-phase formation energies. in continuation, in order to find the origin of longer x−···aromatic ring (x−···cntr) distance than x−···bridgehead nitrogen (x−···napical) in the present complexes, the x−···c6h6 and x−···nh3 systems were simulated, respectively. the calculated interaction energies for two latter systems in different x−···c6h6 and x−···nh3 distances clearly showed that the repulsion force between x− and nitrogen atom is larger than that between x− and aromatic ring. thus, only when there are the strong n–h···x− interactions in top of the cage, the napical···x− distance is considerably smaller than cntr···x− one.