Host-guest complexes of calix[4]tubes--prediction of ion selectivity by quantum chemical calculations VI.
The selectivity of the bis(calix[4]arene)tetraethylene abbreviated as calix[4]tube for the endohedral complexation of alkali and alkaline earth metal ions, was predicted on the basis of structures and complex formation energies computed with three different quantum chemical methods: DFT LANL2DZp)/LANL2DZp), PM3/SPASS, and PM6. A comparison with published X-ray structures demonstrated that the most reliable results were achieved applying DFT calculations. The complexation of K⁺ and Ba²⁺ is most favorable, followed by the encapsulation of Rb⁺ and Sr²⁺, respectively. The flexibility of the tube, described by the torsion angles associated with the ethylene linkages between the calix[4]arene units and phenyl rings intersecting the plane of the four methylene carbon atoms, also makes an important contribution to its selectivity. In general, the cavity size is similar to [2.2.2] and [N2N2N2], the cryptands with the largest cavities previously studied in our group applying a similar protocol.
Inorganic Chemistry, Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Egerlandstr. 1, 91058, Erlangen, Germany.
Svetlana
S
Begel
Ralph
R
Puchta
Rudi
R
van Eldik
D047250:Calixarenes / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008956:Models, Chemical; D011789:Quantum Theory
D007477:Ions; D047250:Calixarenes