Interaction of the univalent thallium cation with antamanide: Experimental and theoretical study

Abstract

On the basis of extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Tl+(aq) + 1·Na+(nb) ⇔1·Tl+ (nb) + Na+(aq) occurring in the two-phase water–nitrobenzene system (1=antamanide; aq=aqueous phase, nb=nitrobenzene phase) was determined as logKex (Tl+, 1·Na+)=0.7±0.1. Further, the stability constant of the 1·Tl+ complex in nitrobenzene saturated with water was calculated for a temperature of 25°C: log βnb (1·Tl+)=4.5±0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the cationic complex species 1·Tl+ was derived. In the resulting complex, the “central” cation Tl+ is bound by four bond interactions to the corresponding four carbonyl oxygen atoms of the parent ligand 1. Besides, the whole 1·Tl+ complex structure is stabilized by two intramolecular hydrogen bonds. The interaction energy of the considered 1·Tl+ complex was found to be −359.0kJ/mol, confirming also the formation of this cationic species.