Curium(III) species and the coordination states in concentrated LiCl-aqueous solutions studied by time-resolved laser-induced fluorescence spectroscopy

Complexation of Cm(III) with Fluoride in Aqueous Solution in the Temperature Range from 20 to 90 °C. A Joint TRLFS and Quantum Chemical Study

“…The Eu(III) chloride complex shows similar distances (see Table ). These results show that due to the elongated bond lengths of the Cm(III)/Eu(III)−chloride complexes, an effective energy transfer to second-shell waters is not possible, which is in good agreement with experimental data …”

“…To validate this assumption, DFT calculations are performed on 9-fold coordinated monofluoro and monochloro complexes, [MX(H 2 O) 8 ] 2+ (H 2 O) 18 (M = Cm, Eu; X = F, Cl). The chloro complexes are introduced because of their analogous structures to those of the fluoro complexes but with the difference that their fluorescence lifetimes have proven to be longer than that of the Cm 3+ aqua ion. , The frequencies of the symmetric and asymmetric vibrational stretching modes involving the second shell hydrogen atoms and the fluoride/chloride ions in the first shell, as well as the corresponding modes of the OH bonds of the first shell water molecules are calculated. Also, the distances of the protons to the halide, to the according oxygen atom, and to the Cm(III)/Eu(III) center ion are obtained.…”

“…Although fluoride forms strong hydrogen bonds with protons from second-shell water molecules, Experimental studies show that such energy transfer mechanism is not observed for the hydrated CmCl 2+ complex, and the lifetime increases according to eq 3. 36,37 For both complexes ([MCl(H 2 O) 8 ] 2+ (H 2 O) 18 (M ) Cm, Eu), the frequencies of the symmetric and asymmetric vibrational stretching modes of the second-shell protons to the chloride ion (3435/3359 cm -1 for Cm(III) and 3548/3462 cm -1 for Eu(III); Figure 3, indices 5 and 8) are comparable to the analogous OH vibrational modes of a first-shell water (3475/3467 cm -1 for Cm(III) and 3567/ 3561 cm -1 for Eu(III); Figure 3, indices 4 and 9). Of more importance are the differences between the fluoride and chloride complexes.…”

Structural and Thermodynamic Properties of the CmIII Ion Solvated by Water and Methanol

“…Curium (Cm) is an important component of spent nuclear fuel and other high-level radioactive wastes; as an element with long-lived α-particle emitting isotopes, Cm is responsible for many of the thermal and radiotoxicological problems associated with the long-term storage of nuclear waste. − The most stable oxidation state is Cm III , leading to behavior that is often generalized to other late actinides . Major research efforts have focused on the separation of Cm 3+ and other trivalent actinides from the trivalent lanthanides using multistage solvent extraction, and thus numerous studies have been conducted regarding solvation of the Cm 3+ ion. − Experimental results, obtained primarily using high-energy X-ray scattering, agree that the hydrated Cm 3+ ion has an average coordination number of 9, in a tricapped trigonal-prismatic geometry.…”

The actinides

“…indicates that the primary hydration number is nine, with a Cm-O bond distance of 2.47-2.48 A ˚.48 Time-resolved laser-induced fluorescence spectroscopic studies of chloride complexation of Cm 3+ have been reported. 49 The structure of Cf(IO 3 ) 3 is the first to be reported for Cf 3+ with oxygen coordination. 50 The separation of later actinides from Ln 3+ using selective complexation to ligands like BTP appears to rely upon greater covalency in the actinide complexes, due to donation from 6d and 5f orbitals that is more important with metals like Cm.…”