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Solvation of europium ions in mixed aqueous-organic solvents was studied in the solutions of europium(III) triflate and chloride. Europium ions are preferentially solvated by organic solvent only in water-dimethylsulfoxide systems. In aqueous dimethylformamide and dimethylacetamide preferential hydration in water-deficient region was observed. The total solvation number was proved to decrease from 9 in neat water to 8 in neat dimethylsulfoxide and dimethylformamide and to 7 in neat dimethylacetamide. The formation of chlorocomplexes in neat water and aqueous dimethylacetamide was observed.

International audience; The 4f-5d transition of Ce3+ provides favorable optical spectroscopic properties such as high sensitivity and quantum yield, making it a most important dopant for lanthanide-activated phosphors. A key for the design of these materials with fine-tuned color emission is a fundamental understanding of the Ce3+ ground state and excited state structures and the dynamics of energy transfer. Such data is also crucial for deriving coordination chemistry information on Ce3+ ions in different chemical environments directly from their optical spectra. Here, by combining 4f-5d absorption and luminescence spectroscopy and highly accurate quantum chemical electronic structure calculations, we study the interplay between the local structure of Ce3+ in aqueous solutions and in crystalline hydrates, the strengths of Ce−O/Cl interactions with aqua and chloride ligands, and the resulting absorption and luminescence spectra. Experimental and theoretical absorption spectra of [Ce(H2O)9]3+ and [Ce(H2O)8]3+ with defined geometries provide a means for analyzing the equilibrium between these species in aqueous solution as a function of temperature (K(298) = 0.20 ± 0.03), while analyses of spectra of different aqua-chloro complexes reveal that eight-coordinate aqua-chloro complexes are present in solution at high chloride concentration. An intriguing feature in these systems concerns the large observed Stokes shifts, 5500−10 100 cm-1. By exploring the excited state potential energy surfaces with relativistic multireference calculations, we show that these shifts result from significant geometrical relaxation processes in the lowest 5d1 excited state. For [*Ce(H2O)8]3+ the relaxation gives shorter Ce−O bonds and a Stokes shift of ∼5500 cm-1, while for [*Ce(H2O)9]3+ the lowest 5d1 state results in a spontaneous dissociation of a water molecule and a Stokes shift of ∼10 100 cm-1. These findings are important for the understanding and optimization of luminescence properties of cerium complexes.

The new compound SrNp(PO(4))(2) (orthorhombic Cmca) has been synthesized by a solid-state reaction and its crystal structure solved ab initio and refined by Rietveld analysis. Though chemically and structurally related to the cheralite CaTh(PO(4))(2), SrNp(PO(4))(2) shows alternate layers of SrO(10) and NpO(8) polyhedra instead of a disordered array of 9-fold polyhedra. Raman and IR spectroscopic measurements also account for ordered cations. This novel structural type allows one to explain the boundaries of the cheralite domain in terms of the cation size and can be proposed as an archetype for a series of other actinide-bearing phosphate compounds.

crystal-field levels of the ground state as sharp and narrowly spaced lines. The total ground-state splittings in 1 (8.0 cm -1 ), 2 (6.0 cm -1 ), and 3 (7.5 cm -1 ) are about three to four times larger than those for Cm 3+ in LaCl3 (2.0 cm -1 ), but four to six times smaller than those for Cm 3+ in [Y(H2O)8]Cl3 ·15-crown-5 (35 cm -1 ). Inhomogeneous line broadening prevents resolving the ground multiplet levels in 4. Vibronic side bands associated with the 8 S′7/2- 6 D′7/2 transition are observed in the low temperature emission and excitation spectra. The intensities of these side bands are

The optical spectra of Cm(3+) incorporated into the crystalline host structure of [Y(H(2)O)(8)]Cl(3).15-crown-5 (1) is investigated by using laser spectroscopic methods at temperatures between 20 and 293 K. The coordination geometry of the [Y(H(2)O)(8)](3+) entity in 1 is a distorted bicapped trigonal prism with approximately C(2) point symmetry, as confirmed by single-crystal X-ray diffraction at 200 K. The crystal-field splitting of the (8)S'(7/2) ground state and the (6)D'(7/2) and (6)P'(5/2) excited states of the hydrated Cm(3+) ion are measured by high-resolution fluorescence emission and excitation spectroscopy at various temperatures. The transitions between the ground state and the respective lowest crystal-field levels of the excited states exhibit narrow fluorescence lines, resolving the four crystal-field levels of the ground state as sharp, well-resolved lines at about 0, 10, 19, and 35 cm(-1). The total splittings of the (6)D'(7/2) and (6)P'(5/2) states are 670 and 170 cm(-1), respectively. Thermal population of the ground-state crystal-field levels is observed and quantified in the excitation spectra in the temperature range of 20-70 K. All spectroscopic results are consistent with the presence of one unique [Cm(H(2)O)(8)](3+) site. The ground-state splitting of Cm(3+) in 1, 35 cm(-1), is comparable to that of Cm(3+) in solid ThO(2), 36 cm(-1), which shows the strongest crystal field for Cm(3+) reported so far. For this reason the present results are different than the findings for Ln(3+) aqua ions, which show rather weak crystal field strengths.

Time-resolved laser fluorescence spectroscopy (TRLFS) is used to study the hydration of the Cm3+ ion in acidified (0.1 M perchloric acid) H2O and D2O from 20 to 200 degrees C. Strong temperature dependency is found for several of the spectroscopic quantities associated with the 6D'(7/2) --> 8S'(7/2) photoemission spectra, with similar relative changes in both solvents. The emission band shifts to lower energy with increasing temperature, which is attributed to an equilibrium between hydrated Cm3+ ions with different numbers of water molecules in the first coordination sphere, namely [Cm(H2O)9]3+ and [Cm(H2O)8]3+. Comparison with crystalline reference compounds and the analysis of hot bands corroborates the assignment of these species. The molar fraction of the octahydrated species increases from approximately 10% at room temperature to approximately 40% at 200 degrees C, indicating an entropy driven reaction. The corresponding thermodynamic parameters are obtained as Delta H degrees = + 13.1 +/- 0.4 kJ mol(-1), Delta S degrees = + 25.4 +/- 1.2 J mol(-1) K(-1), and Delta G298 = + 5.5 +/- 0.6 kJ mol(-1). Both the emission intensity and lifetime decrease with increasing temperature. The temperature dependency of the nonradiative decay rate of the emitting 6D'(7/2) level follows an Arrhenius equation with the activation energy 26.5 kJ mol(-1) (2250 cm(-1)) in both H2O and D2O, which is somewhat lower than the energy gap between 6D'(7/2) and 6P'(5/2) exited state levels.

Surface sensitive grazing incidence XAFS measurements of mineral sorbed metal cations are used to characterize the metal sorbed at reactive surface sites. Two different systems are studied: (1) Hf(IV) sorbed onto the (001) basal plane of freshly cleaved mica and a surface oxidized silicon wafer and (2) U(VI) sorbed onto the (110) surface of α-Al2O3 at two different concentrations and two different orientations of the crystal surface plane to the polarization vector of the incident synchrotron radiation. Similar to findings reported for Hf(IV) sorbed onto amorphous silica, the EXAFS metrical parameters for Hf(IV) on both the mica (001) basal plane and on the oxidized silicon surface show that a mononuclear surface species forms. The cations are bound to silanol/aluminol groups present as defects on the mica surface in a fashion equivalent to binding to clay (hk0) edge sites. The polarization dependency of the XANES/EXAFS spectra of the α-Al2O3 surface sorbed U(VI) uranyl moiety shows that the linear uranyl cations exhibit a preferred orientation on the (110) surface. Comparison of the XANES spectral trends with data previously recorded for UO2(CH3CO2)2·2H2O single crystals and fits to the EXAFS data allows identification of the reactive sites as the AlO6 octahedral edges on the α-Al2O3 (110) surface.

The extended dynamic model of liquid water which considers five different hydrogen-bonded states (including three dominant states) and two major positions of the water molecule in equilibrium, is presented based mostly onthe analysis of near-infrared overtone spectra for the O-D stretching vibration of pure liquid D 2 O, obtained and evaluated within the temperature range of 278 - 358 K (5 - 85 °C). In agreement with the earlier data of Luck and Ditter (1969), and Angell and Rodgers (1984), it was found that the integrated intensity (but not the shape) of the specified (composite) overtone band, situated within the spectral range of 4250 - 5750 cm - 1 , is almost independent of temperature, and displays a quasi-isosbestic point at ca. 5100 cm - 1 . Moreover, the density-corrected difference spectra taken with intervals of 10, 20 and 40 K clearly indicate that the temperature effect is determined by the intensity redistribution between two major components (sub-bands) of the total of five forming the composite overtone contour. These two sub-bands according to their center-of-mass positions, and on the basis of published structural (Bosio et al., 1983), static spectroscopic (Berglund et al., 1978, Walrafen et al., 1986, 1996), and MD simulation (Scortino et al., 1990-1992, Sato and Hirata, 1999) data, can be attributed to the "normal" and temperature-distorted ("T-bifurcated", but not "totally broken") hydrogen-bonded states of O-D oscillators, respectively. In addition, the global Gaussian-contour analysis of obtained composite spectra clearly revealed the existence of O-D oscillator states corresponding to the fraction of presumably pressure-responsive ("P-bifurcated") hydrogen bonds promoted by formation of additional "rigid" five-coordinated water configurations (furnished also by forming of quasi-linear O-O-O trimers within the hexagonal Ih ice-like lattice). The integrated intensity due to this fraction of hydrogen-bonded states does not display any change with temperature, over the whole range of existence of liquid water, as indicated earlier by Luck, Angell, and their co-workers. The whole variety of structural, static spectroscopic, and MD simulation data, together with the results of dielectric relaxation temperature dependence studies (Ronne et al., 1997, 1999, Buchner et al., 1999) can be readily explained in the framework of dynamic "tetrahedral displacement" model first formulated by Agmon (1996). This model implies the temperature-dependent "flip-flop" equilibrium between two major positions for a given water molecule (corresponding to the tetrahedral four-neighbor and the interstitial five-neighbor configurations), the exchange between which is accomplished by the breakage and formation of a net "normal" and a net "T-bifurcated" (and vice versa) hydrogen bond, respectively. The extended van't Hoff analysis indicate that the transition between two states of water at ca. 313 K (40 °C) takes place with almost zero equilibrium free energy, but significant counterbalanced enthalpy and entropy contributions (3.3 kcal mol - 1 and 10.5 cal mol - 1 K - 1 , respectively). In contrast, the effect of high pressure, according to the published data, can be viewed as leading to the "tetrahedral displacements" thanks to the highly-cooperative process of formation of "P-bifurcated" hydrogen bonds only, without altering the quasi-equilibrium between "normal" and "T-bifurcated" fractions.

Theoretical extended X-ray absorption fine structure (EXAFS) spectra have been computed from molecular dynamics (MD) simulation data. Based on MD-generated molecular geometries, EXAFS spectra were generated with the FEFF6 program, commonly used in the analysis of experimental EXAFS spectra. The effects of multiple scattering and second-shell neighbors on the theoretical spectra were evaluated for CaCl2(aq) and AlCl3(aq), i.e., for two solutions with very different cation hydration structures. The effects are significantly larger for the more structured Al3+ solution, The theoretical Ca2+(aq) spectra are compared with new experimental EXAFS data.

The yttrium(III) ion is found by means of extended X-ray absorption fine-structure spectroscopy (EXAFS) and large angle X-ray scattering (LAXS) to be hydrated by eight water molecules in aqueous so...

The formation of hydrated CmF2+ and CmF2+ species in aqueous solutions are studied in the temperature range of 20−90 °C at different fluoride concentrations and at constant ionic strength as well as at constant fluoride concentration and different ionic strengths by means of time-resolved laser fluorescence spectroscopy (TRLFS). The molar fractions of the Cm3+ aqua ion, CmF2+, and CmF2+ species are determined by peak deconvolution of the emission spectra. An increase of the mono- and difluoro complexes is observed with increasing fluoride concentration and/or increasing temperature. Using the specific ion interaction theory (SIT), the thermodynamic stability constants log K10 (CmF2+) and log K20 (CmF2+) as well as the values of Δε1 and Δε2 are determined as a function of temperature. The log K10 values increase from 3.56 ± 0.07 to 3.98 ± 0.06 and the log K20 values increase from 2.20 ± 0.84 to 3.34 ± 0.21 with increasing temperature from 20 to 90 °C. The value of Δε1 determined at 25 °C is in good agreement with literature data and shows a negligible temperature dependency in the studied temperature range. The value of Δε2 also shows only a moderate variation in the studied temperature range. The thermodynamic standard state data (ΔrHm0, ΔrSm0, ΔrGm0) are determined from the temperature dependence of the equilibrium constants at Im = 0 using the integrated Van’t Hoff equation. The fluorescence lifetime of the 6D′7/2(Cm3+) state is found to be constant at 63 ± 5 μs with increasing fluoride concentration. A model based on density functional theory (DFT) calculations is introduced to account for the additional quenching occurring through the near second sphere waters in the [Cm(H2O)8F]2+(H2O)18 complex.

The formation of aqueous Cm(III) nitrate complexes is studied in the temperature range from 5 to 200 °C by time resolved laser fluorescence spectroscopy (TRLFS). The experiments are performed in a custom build high pressure and high temperature fluorescence cell. The complex formation is measured at nitrate concentrations ranging from 0.10 to 4.61 mol/kg H 2 O. The mono- and dinitrate complexes are quantified by peak deconvolution of the fluorescence spectra and the complexation constants are determined as a function of the temperature. The conditional equilibrium constants are extrapolated to zero ionic strength using the specific ion interaction theory (SIT) and the thermodynamic standard state data (Δ r H° m , Δ r S° m , Δ r G° m , Δ r C° p,m ) are determined from the temperature dependence of the equilibrium constants at I = 0. The equilibrium constants up to 75 °C are well described by the Van't Hoff equation (Δ r H° m independent of T and Δ r C° p,m = 0). Modelling of the data at higher temperatures requires an extended equation including a term for the heat capacity changes (Δ r C° p,m ).

The structure of the hydrated gallium(III), indium(III), and chromium(III) ions has been determined in aqueous perchlorate and nitrate solutions by means of the large-angle X-ray scattering (LAXS) and extended X-ray absorption fine structure (EXAFS) techniques. The EXAFS studies have been performed over a wide concentration range, 0.005-1.0 mol.dm(-)(3) (2.6 mol.dm(-)(3) for chromium(III)), while the LAXS studies are restricted to concentrated solutions, ca. 1.5 mol.dm(-)(3). All three metal ions were found to coordinate six water molecules, each of which are hydrogen bonded to two water molecules in a second hydration sphere. The metal-oxygen bond distance in the first hydration sphere of the gallium(III), indium(III), and chromium(III) ions was determined by LAXS and EXAFS methods to be 1.959(6), 2.131(7), and 1.966(8) A. The LAXS data gave mean second sphere M.O distances of 4.05(1), 4.13(1), and 4.08(2) A for the gallium(III), indium(III), and chromium(III) ions, respectively. The perchlorate ion was found to be hydrogen bonded to 4.5(7) water molecules with the O.O distance 3.05(2) A and Cl.O 3.68(3) A. Analyses of the Ga, In, and Cr K-edge EXAFS data of the aqueous perchlorate and nitrate solutions showed no influence on the first shell M-O distance by a change of concentration or anion. The minor contribution from the second sphere M.O distance is obscured by multiple scattering within the tightly bonded first shell. EXAFS data for the alum salts CsM(SO(4))(2).12H(2)O, M = Ga or In, showed the M-O bond length of the hexahydrated gallium(III) and indium(III) ions to be 1.957(2) and 2.122(2) A, respectively.

The structure of the solvated lanthanum(III) ion has been determined in aqueous, dimethyl sulfoxide, and N,N'-dimethylpropyleneurea solution by means of the EXAFS and large-angle X-ray scattering (LAXS) techniques. The close agreement between the EXAFS spectra of solid nonaaqualanthanum(III) trifluoromethanesulfonate and of an aqueous lanthanum(III) perchlorate solution shows that the hydrated lanthanum(III) ion in aqueous solution most probably has the same structure as in the solid, i.e., nine water molecules coordinated in a tricapped trigonal prismatic configuration. The data analysis from EXAFS and LAXS measurements of the aqueous solution resulted in the La-O bond distances 2.52(2) and 2.65(3) A to the water molecules in the prism and the capping positions, respectively. The LAXS study shows a second hydration sphere consistent with approximately 18 water molecules at 4.63(2) A. The EXAFS spectra of solid octakis(dimethyl sulfoxide)lanthanum(III) trifluoromethanesulfonate and a dimethyl sulfoxide solution of this salt are also similar. The data analysis of EXAFS and LAXS measurements assuming eight-coordination around lanthanum yielded an La-O bond distance of 2.50(2) A, and an La...S distance of 3.70(3) A, giving an La-O-S angle of 133(2) degrees. The EXAFS data of an N,N'-dimethylpropyleneurea solution of lanthanum(III) trifluoromethanesulfonate gave the La-O bond distance 2.438(4) A and the La...C distance 3.41(2) A, which correspond to an La-O-C angle of 131(2) degrees. The La-O bond distance is consistent with seven-coordination around lanthanum, on the basis of the variation of the ionic radii of the lanthanum(III) ion with different coordination numbers.