The influence of the bridgehead in Saalfrank-type cryptands: prediction of ion selectivity by quantum chemical calculations XII^†

Abstract

© 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group. We examined the cation selectivity of the Saalfrank-type {2}-metallocryptands [Ga2R3] and [Fe2R3] (R: 1,1'-(pyridine-2,6-diyl)bis(2-(1H-tetrazol-5-yl)ethan-1-one)) with alkaline and earth alkaline metal ions by means of DFT calculations (B3LYP/LANL2DZp) to obtain a better insight into the influence of the bridge head metal ions responsible for the cryptands ion selectivity. Based on our DFT calculations, notably the application of model equations and geometric features regarding the flexibility of the {2}-metallocryptands, we identified K+, Sr2+ and Ba2+ as the best fitting ions. While [Fe2R3] has a cavity a bit larger than [Ga2R3], it prefers the Ba2+ cation, whereas [Ga2R3] selects the smaller Sr2+ cation. The good flexibility of the investigated hosts is provided by the oxygen-donor moieties of the {2}-metallocryptands.