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ISSN 1998-9539

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

Dušan Ćoćić,a,b,c,d Selina Siegl,e Aliya Manaa,e Svetlana Begel,a Colin D. Hubbard,f and Ralph Puchtaa,b,c,e@

aInorganic Chemistry, Department of Chemistry and Pharmacy, University of Erlangen-Nuremberg, 91058 Erlangen, Germany

bCentral Institute for Scientific Computing (ZISC), University of Erlangen-Nuremberg, 91058 Erlangen, Germany

cComputer Chemistry Center, Department of Chemistry and Pharmacy, University of Erlangen-Nuremberg, 91052 Erlangen, Germany

dDepartment of Chemistry, Faculty of Science, University of Kragujevac, 34000 Kragujevac, Serbia

eLothar-von-Faber-Schule, Staatliche Fachoberschule Nürnberg, 90411 Nuremberg, Germany

fDepartment of Chemistry, University of New Hampshire, 03824 New Hampshire, USA

@Corresponding author E-mail: Ralph.Puchta@fau.de

 

Dedicated to the 75th birthday of our friend and teacher Prof. Dr. Dr. h.c. mult. Rudi van Eldik

 

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 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, has in addition an affinity for the third-row alkaline earth cation Mg2+. Therefore, the cavity size must be similar to that of Bühl’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.