Cesium ionophore II as an extraordinarily effective macrocyclic receptor for the barium cation

• Published in: Journal of molecular structure 2015-02, Vol.1081, p.395-399
• Main Authors: Makrlik, Emanuel, Bohm, Stanislav, Vanura, Petr
• Format: Article
• Language: English
• Subjects: Barium cation; Bonding; Cations; Cesium; Cesium ionophore II; Complexation; Constants; DFT calculations; Extraction; Extraction and stability constants; Macrocyclic compounds; Mathematical analysis; Nitrobenzenes; Receptors; Structures
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2014.10.040

[Display omitted] •Extremely high stability of the cesium ionophore II – Ba2+ complex was determined.•Quantum mechanical DFT calculations were applied.•Structure of the resulting complex was predicted. On the basis of extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Ba2+(aq)+2ClO4−(aq)+1(nb) ⇄1·Ba2+(nb)+2ClO4− (nb) occurring in the two-phase water–nitrobenzene system (1=cesium ionophore II; aq=aqueous phase, nb=nitrobenzene phase) was evaluated as logKex (1·Ba2+, 2ClO4−)=3.4±0.1. Further, the extremely high stability constant of the 1·Ba2+ complex in nitrobenzene saturated with water was calculated for a temperature of 25°C: logβnb (1·Ba2+)=16.7±0.1. Finally, applying quantum mechanical DFT calculations, the most probable structure of the cationic complex species 1·Ba2+ was derived. In the resulting 1·Ba2+ complex, the “central” cation Ba2+ is bound by four very strong bonding interactions to the respective four oxygen atoms of the parent receptor 1. The interaction energy, E(int), of the considered 1·Ba2+ complex was found to be −1050.4kJ/mol, confirming also the formation of this significant complex.