Hybridization makes the difference: [2_Oxa.2_Oxa.2_Oxa] a sp²-Carbon dominated Lehn-type cryptand - Prediction of ion selectivity by quantum chemical calculations. XVIII

Abstract

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 ⊂ 2_Oxa.2_Oxa.2_Oxa]^m+. We explored by quantum chemical methods (B3LYP/LANL2DZp) the complexation behaviour and compared it with the original cryptand [2.2.2]. The cryptands [2_Oxa.2_Oxa.2_Oxa] 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 [2_Oxa.2_Oxa.2_Oxa] less flexible in the OCCO-diether angle as [2.2.2]. This rigidity results in higher complexation energies for [M ⊂ 2_Oxa.2_Oxa.2_Oxa]^m+ and that the twisting of the dihedral angle CN…NC improves the nesting of the guest cations in the cryptand [2_Oxa.2_Oxa.2_Oxa].

Keywords:

• selective ion complexation
• cryptand
• DFT-study
• reaction mechanisms
  

Acknowledgments

D.Ć. thanks the Ministry of Education, Science and Technological Development of the Republic of Serbia (Agreement No. 451-03-68/2020-14/200122). We would like to thank Prof. Tim Clark and Prof. Petra Imhof for hosting this work at the CCC. The authors gratefully acknowledge the Regionales Rechenzentrum Erlangen (RRZE) for a generous allotment of computer time.

Disclosure statement

No potential conflict of interest was reported by the authors.