Evidence of different stoichiometries for the limiting carbonate complexes across the lanthanide(III) series: A capillary electrophoresis‐mass spectrometry study

Abstract

The electrophoretic mobilities (mu ep,Ln) of twelve lanthanides (not Ce, Pr and Yb) were measured by CE-ICP-MS in 0.15 and 0.5 mol L(-1) Alk2 CO3 aqueous solutions for Alk+ = Li+, Na+, K+ and Cs+. In 0.5 mol L(-1) solutions, two different mu ep,Ln values were found for the light (La to Nd) and the heavy (Dy to Tm) lanthanides, which suggests two different stoichiometries for the carbonate limiting complexes. These results are consistent with a solubility study that attests the Ln(CO3)3(3-) and Ln(CO3)4(5-) stoichiometries for the heavy (small) and the light (big) lanthanides, respectively. The Alk+ counterions influence the mu ep,Ln Alk2 CO3 values, but not the overall shape of the mu ep,Ln Alk2 CO3 plots as a function of the lanthanide atomic numbers: the counterions do not modify the stoichiometries of the inner sphere complexes. The influence of the Alk+ counterions decreases in the Li+ > Na+ >> K+ > Cs+ series. The K3,Ln stepwise formation constants of the Ln(CO3)3(3-) complexes slightly increase with the atomic numbers of the lanthanides while K4,Ln, the stepwise formation constants of Ln(CO3)4(5-) complexes, slightly decrease from La to Tb, and is no longer measurable for heavier lanthanides.

Direct determination of plutonium(V) and neptunium(V) complexation by carbonate ligand with CE‐ICP‐sector field MS

“…, which is consistent with recent experimental results suggesting that for highly charged species, stabilization occurs by ion pairing [27]. The determination is consistent with the mobility of lanthanide carbonate obtained by Philippini et al at a comparable ionic strength, 0.5 mol/L.…”

Lanthanide Carbonates

“…The thermodynamic stability constants that were obtained from the extraction and potentiometry methods and, particularly, from the solubility studies of Na[Ln(CO 3 3-seems to be the limiting complex. [5,8,9] We decided to investigate the speciation of the carbonates by taking advantage of the analysis of the f-f transitions, which has previously been successfully applied to identify the structure and stoichiometry of various complexes in aqueous solution. [23] The analysis of the UV/Vis/NIR absorption spectra led to certain conclusions about the stoichiometry of the complexes and the coordination modes of the carbonate anions.…”

“…ues for the ν 1 band maxima in the respective spectra for the II crystals and solutions (lower arrow in Figure 10) may suggest that the geometry of the complexes and the coordi- nation number of the heavy Ln 3+ ions (8) are similar in both phases. Because the resolution of the light lanthanide spectra was worse, it is difficult to draw similar conclusions about the composition of the metal first coordination sphere for these systems.…”

“…On the other hand, the measurements of the electrophoretic mobilities and solubilities of Na[Eu(CO 3 ) 2 ]·nH 2 O, which was performed by Philippini et al, [8,9] indicated different complex stoichiometries for the light ([Ln(CO 3 ) 4 ] 5-) and heavy ([Ln(CO 3 ) 3 ] 3-) lanthanides. These differences were explained by the lanthanide contraction.…”

Formation of CaSO4(aq) and CaSeO4(aq) studied as a function of ionic strength and temperature by CE

“…detection. The use of inductively coupled plasma mass spectrometers has also enabled low-level detection of lanthanides or actinides in studies aiming at determining their carbonate complexation constants [16,17]. With commercial CE instruments, it is now possible to perform measurements at a 5-601C temperature range enabling to determine thermodynamic parameters such as entropy and enthalpy of reactions, which have never yet been done with inorganic systems and require a precise control of the effective temperature inside the capillary.…”