Ab initio calculations of electronic interactions in inclusion complexes of calix- and thiacalix[n]arenes and block s cations

Ab initio calculations at the HF/6-31G(d) level of theory were performed on a series of thiacalix4]arenes and calix6]arenes in presence and in absence of monovalent (Li⁺, Na⁺ and Cs⁺) and divalent cations (Ca²⁺ and Ba²⁺) respectively, in order to evaluate their particular bonding properties as host systems towards electrically charged species. NBO, as well as NBO deletion calculations were undertaken to evaluate the energy difference in the circular hydrogen bonding at the lower rim once an ion was placed inside the cavity. Disruption of this H-bonded system is dependent on the position of the ion within the guest and not on its ionic ratio. The basis set superposition error and the NBO deletion energy between the host and guest species were calculated in order to assess the interaction energy between them.