Hybridization makes the difference: [2 Oxa .2 Oxa .2 Oxa ] a sp ² -Carbon dominated Lehn-type cryptand - Prediction of ion selectivity by quantum chemical calculations. XVIII

This is the authors' abstract. We don't add key points for this paper.

Substituting the O-C2H4-O-moiety of [2.2.2] by the O2CCO2-core of oxalic acid leads to the new Lehn-type cryptand [M ⊂ 2Oxa.2Oxa.2Oxa]m+. We explored by quantum chemical methods (B3LYP/LANL2DZp) the complexation behaviour and compared it with the original cryptand [2.2.2]. The cryptands [2Oxa.2Oxa.2Oxa] and [2.2.2] exhibit the same ion selectivity against alkaline and alkaline earth metal cation (K+ followed by Rb+; Ba2+ preferred over Sr2+). The exchange of the OC2H4O-moiety by the O2CCO2-moiety (the subsequent exchange of sp3- by sp2-carbon atoms) makes [2Oxa.2Oxa.2Oxa] less flexible in the OCCO-diether angle as [2.2.2]. This rigidity results in higher complexation energies for [M ⊂ 2Oxa.2Oxa.2Oxa]m+ and that the twisting of the dihedral angle CN…NC improves the nesting of the guest cations in the cryptand [2Oxa.2Oxa.2Oxa].