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RESEARCH PRODUCT

An ab Initio MO Study of Silver Triflate Complexation in [2.2.1]Cyclophane π-Prismands

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Ab initio Hartree-Fock and DFT MO calculations have been used to study the conformations of six [2.2.1]cyclophane π-prismands and the formation of their π-complexes with silver triflate (AgSO 3 CF 3 ). The lowest energy cyclophane conformations and their silver triflate π-complexes have been calculated with HF/3-21G* and B3LYP/3-21G* levels of theory. The nature of bonding in silver triflate π-complexes has been studied with natural bond orbital analysis (NBO). Energies of the calculated cyclophanes and complexes, together with the formation energies of those complexes, have also been discussed. The results have been compared to available X-ray crystal structures and also to results of the previously published ab initio calculations of slightly larger [2.2.2]cyclophanes and their silver complexes. Calculated and experimental X-ray structures agreed reasonably well, given the rather small 3-21G* basis set. Changes in the bonding between the ligand and Ag + ion were observed, due to an enhanced bonding of the triflate moiety over the silver atom ion in the calculated models. In these complexes the silver ion is bonded to the cyclophane cavity by the bonds formed by a donation and d-π* back-donation between the silver ion and the hydrocarbon skeleton resulting in variable bonding modes from η 1 to η 6 per aromatic ring depending on the ligand conformation. In this case the a donation from the hydrocarbon to the silver ion is the main contribution to the metal-cyclophane bonding. Bonding of the silver ion to the present π-prismands relates by strength to a single moderately strong hydrogen bond and varies between 25 and 50 kJ/mol. Due to the smaller cavity, the more rigid hydrocarbon skeleton, and the presence of the triflate moiety [2.2.1]cyclophanes form different types of interactions with silver ion when compared to previously published [2.2.2]cyclophane π-prismand complexes with Ag + ion.