Host-Guest Complexes of Two Isomeric 2,2 '-Bioxazole Based {2}-Lehn-Type Cryptands. Prediction of Ion Selectivity by Quantum Chemical Calculations. Part XIV

摘要

The two isomeric cryptands 1 (N,N'-bis(2,2'-bioxazole-5,5 '-dimethyl)-2,2'-bioxazole-5,5 '-bis(methylamine)) and 2 (N,N '-bis(2,2 '-bioxazole-4,4'-dimethyl)-2,2'-bioxazole-4,4 '-bis(methylamine)) were investigated by DFT-calculations (RB3LYP/LANL2DZp). Based on these structures and energies we have determined with model equations and by structural comparison with solvent complexes ([M(Furan)(n)](m)(+), [M(Pyridine)(n)](m)(+) and [M(NH3)(n)](m)(+)) the ion selectivity of 1 and 2. 1 exhibits preferences for the sodium cation and the calcium dication, nearly equally with the strontium dication. Therefore, 1 has a cavity comparable to [phen.phen.phen]. In contrast, cryptand 2, although it also shows a preference for the third-row sodium cation, for the third-row alkaline earth cation Mg2+. Therefore, the cavity size must be similar to that of Buhl's cryptand dodeka(ethylene)octamine and [2.1.1]. We attribute this difference in selectivity to the longer Mm+-N-interactions in 2 compared to Mm+-O-interactions in 1.