An Anomalous X-ray Diffraction Study of Yttrium(III) Hydration

Hydration and ion pair formation in aqueous Y(3+)-salt solutions

Raman spectra of aqueous yttrium perchlorate, triflate (trifluoromethanesulfonate), chloride and nitrate solutions were measured over a broad concentration range (0.198-3.252 mol L(-1)). The spectra range from low wavenumbers to 4200 cm(-1). A very weak mode at 384 cm(-1) with a full width at half height at 50 cm(-1) in the isotropic spectrum suggests that the Y(3+)- octa-aqua ion is thermodynamically stable in dilute perchlorate solutions (∼0.5 mol L(-1)) while in concentrated perchlorate solutions outer-sphere ion pairs and contact ion pairs are formed. The octa-hydrate, [Y(OH2)8](3+) was also detected in a 1.10 mol L(-1) aqueous Y(CF3SO3)3 solution. Furthermore, very weak and broad depolarized modes could be detected which are assigned to [Y(OH2)8](3+)(aq) at 100, 166, 234 and 320 cm(-1) confirming that a hexa-hydrate is not compatible with the hydrated species in solution. In yttrium chloride solutions contact ion pair formation was detected over the measured concentration range from 0.479-3.212 mol L(-1). The contact ion pairs in YCl3(aq) are fairly weak and disappear with dilution. At a concentration <0.2 mol L(-1) almost all complexes have disappeared. In YCl3 solutions, with additional HCl, chloro-complexes of the type [Y(OH2)8-nCln](+3-n) (n = 1,2) are formed. The Y(NO3)3(aq) spectra were compared with a spectrum of a dilute NaNO3 solution and it was concluded that in Y(NO3)3(aq) over the concentration range from 2.035-0.198 mol L(-1) nitrato-complexes [Y(OH2)8-n(NO3)ln](+3-n) (n = 1,2) are formed. The nitrato-complexes are weak and disappear with dilution <0.1 mol L(-1). DFT geometry optimizations and frequency calculations are reported for both the yttrium-water cluster in the gas phase and the cluster within a polarizable continuum model in order to implicitly describe the presence of the bulk solvent. The bond distance and angle for the square antiprismatic cluster geometry of [Y(OH2)8](3+) with the polarizable dielectric continuum is in good agreement with data from recent structural experimental measurements. The DFT frequency of the Y-O stretching mode of the [Y(OH2)8](3+) cluster, in a polarizable continuum, is at 372 cm(-1) in satisfactory agreement with the experimental value.

Production and separation of 97Ru and coproduced 95Tc from 12C-induced reaction on yttrium target

An attempt has been made to produce no-carrier-added (nca) 97Ru for the first time from the 12C-induced reaction on yttrium target. A natY foil of 10 mg/cm2 thickness was irradiated by 75 MeV 12C beams for 3.5 h and a thick target yield of 514 kBq/μA h for 97Ru and 338 kBq/μA h for 95Tc was achieved. The nca 97Ru and coproduced nca 95Tc were then radiochemically separated from the bulk target by liquid–liquid extraction (LLX). Liquid cation exchanger di-(2-ethylhexyl)phosphoric acid (HDEHP), liquid anion exchanger trioctylamine (TOA) were used in this study. The technique offers efficient chemical separation of the products, resulting in very high separation factors.

Y(III) interactions with guanine oligonucleotides covalently attached to aqueous/solid interfaces

The binding of Y(III) ions to surface-immobilized single-stranded 20-mers of guanine was studied using the Eisenthal χ((3)) technique and AFM. The free energy of binding for Y(III) to the G(20) sequence was found to be -39.5(8) kJ/mol. Furthermore, yttrium binds much more strongly to surface-immobilized oligonucleotides than the divalent metals previously reported. At maximum surface coverage, Y(III) ion densities range between one to three ions bound per strand. Comparatively, Mg(II) binds to the G(20)-functionalized interface in much higher ion densities. This result may be explained, in part, by the larger hydration sphere radius of Y(III) compared to that of Mg(II). The ion loading and binding free energy results, in conjunction with other surface and bulk aqueous phase studies, suggest that a fully hydrated +2 or +3 yttrium ion binds to the oligonucleotides through an outer-sphere mechanism. Tapping mode AFM results indicate that oligonucleotide height does not appreciably decrease following Y(III) binding. These results, together with the low ion densities for Y(III) ions, indicate that Y(III) strand loading may not significantly decrease the intrastrand Coulombic repulsions in order to cause a significant decrease in oligomer height.

Local Structure Refinement of Disordered Material Models: Ion Pairing and Structure in YCl3 Aqueous Solutions

Hydrogen/deuterium isotopic neutron diffraction techniques have been used to investigate the structure of a 1 m aqueous solution of YCl3 at room temperature. Empirical potential structure refinement (EPSR) has been used to build a three-dimensional model of the solution structure that is consistent with the bulk solvent correlations strongly probed by the neutron scattering technique. Optimization of the local structural environment of the Y3+ ion sites within the model has been performed through calculations of the yttrium K-edge, extended X-ray absorption fine structure (EXAFS) spectrum of the solution, and detailed information has been extracted on the structure of the ion hydration shell and the extent of inner-sphere ion pairing within the solution. The results demonstrate the significant potential of this hybrid data analysis approach to circumvent the limitations of the individual experimental methods, to refine atomic potential models, and to produce accurate, quantitative structural models of the local environment of dilute atomic species within tightly constrained bulk network structures.

An anomalous x-ray diffraction study of the hydration structures of Cs+ and I− in concentrated solutions

Anomalous x-ray diffraction experiments were carried out on concentrated aqueous solutions of sodium iodide (6 molal) and cesium iodide (3 molal). Data were gathered at two energies below the absorption edges of the Cs+ and I- ions in order to avoid contributions from fluorescence. The statistics and quality of the raw data were improved by the use of a focusing analyzer crystal. Differences were taken between the data sets and used to calculate the hydration structures of Cs+ and I-. The structures found are more complex than anticipated for such large ions with relatively low charge densities and show evidence of ion-pair formation in both solutions. A two-Gaussian fit to the Cs+ data gives information about the Cs+-O and Cs+-I- correlations. The central position of the Gaussian representing the Cs+-O was fixed at 3.00 A, that is, the maximum of this contribution. The other parameters were allowed to vary freely, giving a Cs+-I- distance of 3.84+/-0.05 A and coordination numbers of 7.9 and 2.7, respectively, for the Cs+-O and Cs+-I- correlations. The results on the structure of I- in the 6 molal NaI aqueous solution were also fitted to a model based on Gaussians; this gives correlations for I- -O and I- -Na+ at 3.17+/-0.06 and 3.76+/-0.06 A with respective coordination numbers of 8.8 and 1.6. The structure of I- in the 3 molal CsI solution shows overlapping contributions due to I- -H, I- -O, and I- -Cs+. The best Gaussian fit gives two peaks centered at 3.00+/-0.08 and 3.82+/-0.04 A and shows that the latter two correlations are unresolved. The hydration structures are compared with those of other alkali and halide ions. The results are also found to be in good agreement with those obtained from standard x-ray diffraction and computer simulation.