First Experimentally Determined Thermodynamic Values of Francium: Hydration Energy, Energy of Partitioning, and Thermodynamic Radius

• Published in: The journal of physical chemistry. B Vol. 117; no. 31; pp. 9258 - 9261
• Main Authors: Delmau, Lætitia H, Moine, Jérôme, Mirzadeh, Saed, Moyer, Bruce A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 08.08.2013
• Subjects: Chemical thermodynamics; Chemistry; Complexation; Constants; Energy of solution; Exact sciences and technology; Francium; General and physical chemistry; Hydration; Partitioning; Solvents; Thermodynamics; Cation exchange; Ionic radius; Hydration; Francium; Immiscible
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp401880f

The Gibbs energy of partitioning of Fr+ ion between water and nitrobenzene has been determined to be 14.5 ± 0.6 kJ/mol at 25 °C, the first ever Gibbs energy of partitioning for francium in particular and the first ever solution thermodynamic quantity for francium in general. This value enabled the ionic radius and standard Gibbs energy of hydration for Fr+ to be estimated as 173 pm and −251 kJ/mol, respectively, the former value being significantly smaller than previously thought. A new experimental method was established using a cesium dicarbollide as a cation-exchange agent, overcoming problems inherent to the trace-level concentrations of francium. The methodology opens the door to the study of the partitioning behavior of francium to other water-immiscible solvents and the determination of complexation constants for francium binding by receptor molecules.