Alkali-metal ion coordination in uranyl(VI) ...
Type de document :
Compte-rendu et recension critique d'ouvrage
DOI :
Titre :
Alkali-metal ion coordination in uranyl(VI) poly- peroxide complexes in solution. Part 1: the Li<sup>+</sup>, Na<sup>+</sup> and K<sup>+</sup> – peroxide–hydroxide systems
Auteur(s) :
Zanonato, Pier Luigi [Auteur]
Dipartimento di Scienze Chimiche [Padova]
Di Bernardo, Plinio [Auteur]
Dipartimento di Scienze Chimiche [Padova]
Vallet, Valérie [Auteur]
Physico-Chimie Moléculaire Théorique [PCMT]
Szabó, Zoltan [Auteur]
Grenthe, Ingmar [Auteur]
Dipartimento di Scienze Chimiche [Padova]
Di Bernardo, Plinio [Auteur]
Dipartimento di Scienze Chimiche [Padova]
Vallet, Valérie [Auteur]
Physico-Chimie Moléculaire Théorique [PCMT]
Szabó, Zoltan [Auteur]
Grenthe, Ingmar [Auteur]
Titre de la revue :
Dalton Transactions
Pagination :
1549
Éditeur :
Royal Society of Chemistry
Date de publication :
2015-01-28
ISSN :
1477-9226
Discipline(s) HAL :
Physique [physics]/Physique [physics]/Chimie-Physique [physics.chem-ph]
Résumé en anglais : [en]
The alkali metal ions Li<sup>+</sup>, Na<sup>+</sup> and K<sup>+</sup> have a profound influence on the stoichiometry of the complexes formed in uranyl(VI)–peroxide–hydroxide systems, presumably as a result of a templating ...
Lire la suite >The alkali metal ions Li<sup>+</sup>, Na<sup>+</sup> and K<sup>+</sup> have a profound influence on the stoichiometry of the complexes formed in uranyl(VI)–peroxide–hydroxide systems, presumably as a result of a templating effect, resulting in the formation of two complexes, M[(UO<sub>2</sub>)(O<sub>2</sub>)(OH)]<sup>2−</sup> where the uranyl units are linked by one peroxide bridge, μ-η<sub>2</sub>-η<sub>2</sub>, with the second peroxide coordinated “end-on”, η<sub>2</sub>, to one of the uranyl groups, and M[(UO<sub>2</sub>)(O<sub>2</sub>)(OH)]<sub>4</sub><sup>3-</sup>, with a four-membered ring of uranyl ions linked by μ-η<sub>2</sub>-η<sub>2</sub> peroxide bridges. The stoichiometry and equilibrium constants for the reactions: M<sup>+</sup> + 2UO<sub>2</sub><sup>2+</sup> + 2HO<sub>2</sub><sup>−</sup> + 2H<sub>2</sub>O → M[(UO<sub>2</sub>)(O<sub>2</sub>)(OH)]<sub>2</sub><sup>−</sup> + 4H<sup>+</sup> (1) and M<sup>+</sup> + 4UO<sub>2</sub>2<sup>+</sup> + 4HO<sub>2</sub><sup>−</sup> + 4H<sub>2</sub>O → M[(UO<sub>2</sub>)(O<sub>2</sub>)(OH)]<sub>4</sub><sup>3−</sup> + 8H<sup>+</sup> (2) have been measured at 25 °C in 0.10 M (tetramethyl ammonium/M+)NO<sub>3</sub> ionic media using reaction calorimetry. Both reactions are strongly enthalpy driven with large negative entropies of reaction; the observation that ΔH(2) ≈ 2ΔH(1) suggests that the enthalpy of reaction is approximately the same when peroxide is added in bridging and “end-on” positions. The thermodynamic driving force in the reactions is the formation of strong peroxide bridges and the role of M<sup>+</sup> cations is to provide a pathway with a low activation barrier between the reactants and in this way “guide” them to form peroxide bridged complexes; they play a similar role as in the synthesis of crown-ethers. Quantum chemical (QC) methods were used to determine the structure of the complexes, and to demonstrate how the size of the M<sup>+</sup>-ions affects their coordination geometry. There are several isomers of Na[(UO<sub>2</sub>)(O<sub>2</sub>)(OH)]<sub>2</sub><sup>-</sup> and QC energy calculations show that the ones with a peroxide bridge are substantially more stable than the ones with hydroxide bridges. There are isomers with different coordination sites for Na<sup>+</sup> and the one with coordination to the peroxide bridge and two uranyl oxygen atoms is the most stable one.Lire moins >
Lire la suite >The alkali metal ions Li<sup>+</sup>, Na<sup>+</sup> and K<sup>+</sup> have a profound influence on the stoichiometry of the complexes formed in uranyl(VI)–peroxide–hydroxide systems, presumably as a result of a templating effect, resulting in the formation of two complexes, M[(UO<sub>2</sub>)(O<sub>2</sub>)(OH)]<sup>2−</sup> where the uranyl units are linked by one peroxide bridge, μ-η<sub>2</sub>-η<sub>2</sub>, with the second peroxide coordinated “end-on”, η<sub>2</sub>, to one of the uranyl groups, and M[(UO<sub>2</sub>)(O<sub>2</sub>)(OH)]<sub>4</sub><sup>3-</sup>, with a four-membered ring of uranyl ions linked by μ-η<sub>2</sub>-η<sub>2</sub> peroxide bridges. The stoichiometry and equilibrium constants for the reactions: M<sup>+</sup> + 2UO<sub>2</sub><sup>2+</sup> + 2HO<sub>2</sub><sup>−</sup> + 2H<sub>2</sub>O → M[(UO<sub>2</sub>)(O<sub>2</sub>)(OH)]<sub>2</sub><sup>−</sup> + 4H<sup>+</sup> (1) and M<sup>+</sup> + 4UO<sub>2</sub>2<sup>+</sup> + 4HO<sub>2</sub><sup>−</sup> + 4H<sub>2</sub>O → M[(UO<sub>2</sub>)(O<sub>2</sub>)(OH)]<sub>4</sub><sup>3−</sup> + 8H<sup>+</sup> (2) have been measured at 25 °C in 0.10 M (tetramethyl ammonium/M+)NO<sub>3</sub> ionic media using reaction calorimetry. Both reactions are strongly enthalpy driven with large negative entropies of reaction; the observation that ΔH(2) ≈ 2ΔH(1) suggests that the enthalpy of reaction is approximately the same when peroxide is added in bridging and “end-on” positions. The thermodynamic driving force in the reactions is the formation of strong peroxide bridges and the role of M<sup>+</sup> cations is to provide a pathway with a low activation barrier between the reactants and in this way “guide” them to form peroxide bridged complexes; they play a similar role as in the synthesis of crown-ethers. Quantum chemical (QC) methods were used to determine the structure of the complexes, and to demonstrate how the size of the M<sup>+</sup>-ions affects their coordination geometry. There are several isomers of Na[(UO<sub>2</sub>)(O<sub>2</sub>)(OH)]<sub>2</sub><sup>-</sup> and QC energy calculations show that the ones with a peroxide bridge are substantially more stable than the ones with hydroxide bridges. There are isomers with different coordination sites for Na<sup>+</sup> and the one with coordination to the peroxide bridge and two uranyl oxygen atoms is the most stable one.Lire moins >
Langue :
Anglais
Vulgarisation :
Non
Projet ANR :
Source :