Coordination chemistry of trivalent lanthanide and actinide ions in dilute and concentrated chloride solutions

Journal Article · Mon Feb 07 04:00:00 EST 2000 · Inorganic Chemistry

DOI:https://doi.org/10.1021/ic9905953· OSTI ID:20017282

Allen, P G; Bucher, J J; Shuh, D K; Edelstein, N M; Craig, I

The authors have used EXAFS spectroscopy to investigate the inner sphere coordination of trivalent lanthanide (Ln) and actinide (An) ions in aqueous solutions as a function of increasing chloride concentrations. At low chloride concentration, the hydration numbers and corresponding Ln,An-O bond lengths are as follows: La{sup 3+}, N = 9.2, R = 2.54{angstrom}; Ce{sup 3+}, N = 9.3, R = 2.52{angstrom}; Nd{sup 3+}, N = 9.5, R = 2.49{angstrom}; Eu{sup 3+}, N = 9.3, R = 2.43{angstrom}; Yb{sup 3+}, N = 8.7, R = 2.32{angstrom}; Y{sup 3+}, N = 9.7, R = 2.36{angstrom}; Am{sup 3+}, N = 10.3, R = 2.48{angstrom}; Cm{sup 3+}, N = 10.2, R = 2.45{angstrom}. In ca. 14 M LiCl, the early Ln{sup 3+} ions (La, Ce, Nd, and Eu) show inner sphere Cl{sup {minus}} complexation along with a loss of H{sub 2}O. The average chloride coordination numbers and Ln-Cl bond lengths are as follows: La{sup 3+}, N = 2.1, R = 2.92{angstrom}; Ce{sup 3+}, N = 1.8, R = 2.89{angstrom}; Nd{sup 3+}, N = 1.9, R = 2.85{angstrom}; Eu{sup 3+}, N = 1.1, R = 2.81{angstrom}. The extent of Cl{sup {minus}} ion complexation decreases going across the Ln{sup 3+} series to the point where Yb{sup 3+} shows no Cl{sup {minus}} complexation and no loss of coordinated water molecules. The actinide ions, Am{sup 3+} and Cm{sup 3+}, show the same structural effects as the early Ln{sup 3+} ions, i.e., CL{sup {minus}} ion replacement of the H{sub 2}O at high chloride thermodynamic activities. The Cl{sup {minus}} ion coordination numbers and An-Cl bond lengths are: Am{sup 3+}, N = 1.8, R = 2.81{angstrom}; Cm{sup 3+}, N = 2.4, R = 2.76{angstrom}. When combined with results reported previously for Pu{sup 3+} which showed no significant chloride complexation in 12 M LiCl, these results suggest that the extent of chloride complexation is increasing across the An{sup 3+} series. The origin of the differences in chloride complex formation between the Ln{sup 3+} and An{sup 3+} ions and the relevance to earlier work is discussed.

• Research Organization: Lawrence Berkeley National Lab., CA (US)
• Sponsoring Organization: US Department of Energy
• DOE Contract Number: AC03-76SF00098; W-7405-ENG-48
• OSTI ID: 20017282
• Journal Information: Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 3 Vol. 39; ISSN 0020-1669; ISSN INOCAJ
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABUNDANCE
ACTINIDES
AQUEOUS SOLUTIONS
BOND LENGTHS
CHLORIDES
COORDINATION VALENCES
HYDRATION
RARE EARTHS