1,721,283 research outputs found
Bookreview: Unfit for the Future (by Ingmar Persson and Julian Savulescu)
No full textBookreview of 'Unfit for the Future' by Ingmar Persson and Julian Savalesc
Structure of the hydrated and dimethyl sulfoxide solvated rubidium ions in solution
No full textThe structure of the hydrated and the dimethyl sulfoxide solvated rubidium ions in solution has been determined by means of large-angle X-ray scattering (LAXS) and extended X-ray absorption fine structure (EXAFS) studies. The models of the hydrated and dimethyl sulfoxide solvated rubidium ions fitting the experimental data best are square antiprisms with Rb-O bond distances of 2.98(2) and 2.98(3) Angstrom, respectively. The EXAFS data show a significant asymmetry in the Rb-O bond distance distribution with C-3 values of 0.0076 and 0.015 Angstrom(3), respectively. No second hydration sphere is observed around the hydrated rubidium ion. The dimethyl sulfoxide solvated rubidium ion displays a Rb-O-S bond angle of ca. 130degrees, which is typical for a medium hard electron acceptor such as rubidium
Analysis of the Detailed Configuration of Hydrated Lanthanoid(III) Ions in Aqueous Solution and Crystalline Salts by Using K- and L-3-Edge XANES Spectroscopy
No full textThe structural properties of the hydrated lanthanoid(III) ions in aqueous solution and in the isostructural trifluoromethanesulfonate salts have been investigated by a quantitative analysis of the X-ray absorption near-edge structure (XANES) spectra at the K- and L-3-edges. The XANES analysis has provided a clear description of the variation of lanthanoid(III) hydration properties across the series. It was found that all of the lanthanoid(III) hydration complexes retain a tricapped trigonal prism (TTP) geometry, and along the series two of the capping water molecules become less and less strongly bound. before finally, oil average, one of them leaves the hydration cluster. This gives rise to an eight-coordinated distorted bicapped trigonal prism with two different Ln-O capping distances for the smallest lanthanoid(111) ions. This systematic study has shown that for lanthanoid compounds more accurate structural information is obtained from the analysis of the L-3-edge than from K-edge XANES data. Moreover. whereas the second hydration shells provide a detectable contribution to the L-3-edge XANES spectra of the lighter lanthanoid ions, the Kedge spectra are insensitive to the more distant coordination spheres
Structural investigation of lanthanoid coordination: A combined XANES and molecular dynamics study
No full textThis is the first systematic study exploring the potentiality of the X-ray absorption near edge structure (XANES) technique as a structural tool for systems containing lanthanoid(III) Ions. A quantitative analysis of the XANES spectra at the K- and L3-edges has been carried out for three hydrated lanthanoid(III) ions, namely, Yb, Nd, and Gd, in aqueous solution and in the isostructural trifluoromethanesulfonate salts. The structural and dynamic properties of the hydrated lanthanoid(III) ions in aqueous solution have been investigated by a combined experimental-theoretical approach employing X-ray absorption spectroscopy and molecular dynamics (MD) simulations. This method allows one to perform a quantitative analysis of the XANES spectra of ionic solutions using a proper description of the thermal and structural fluctuations. XANES spectra have been computed starting from the MD trajectory, without carrying out any minimization in the structural parameter space. A comparative K- and L3-edge XANES data analysis is presented, demonstrating the clear advantages of the L3-edge XANES analysis over the K-edge studies for structural investigations of lanthanold compounds. The second hydration shells provide a detectable contribution to the L3-edge spectra while the K-edge data are insensitive to the more distant coordination spheres because of the strong damping and broadening of the signal caused by the extremely large core hole widths. The XANES technique has been found to be a new valuable tool for the structural characterization of metal complexes both in the solid and in the liquid state, especially in the presence of low symmetry. © 2009 American Chemical Society
K-edge XANES investigation of octakis(DMSO)lanthanoid(iii) complexes in DMSO solution and solid iodides
No full textThe potential of high energy XANES (X-ray absorption near edge structure) as a tool for the structural analysis of lanthanoid-containing systems has been explored. The K-edge XANES spectra of La3+, Gd3+, and Lu3+ ions both in DMSO solution and solid octakis(DMSO) lanthanoid(III) iodides have been analysed. Although the K-edges of lanthanoids cover the energy range of 38 (La) to 65 (Lu) keV, the large widths of the core hole states do not appreciably reduce the potential structural information of the XANES data. We show that, for lanthanoid compounds, accurate structural parameters are obtained from the analysis of K-edge XANES signals if a deconvolution procedure is carried out. We found that in solid octakis(DMSO) lanthanoid(III) iodides the Ln(3+) ions are coordinated by eight DMSO ligands arranged in a quite symmetric fashion. In DMSO solution the Ln(3+) ions retain a regular eight-coordination structure and the coordination number does not change along the series. In contrast to when in water the second coordination shell has been found to provide a negligible contribution to the XANES spectra of Ln(3+) ions in DMSO solution
Structural Study of the N,N '-Dimethylpropyleneurea Solvated Lanthanoid(III) Ions in Solution and Solid State with an Analysis of the Ionic Radii of Lanthanoid(III) Ions
No full textThe structures of the N,N'-dimethylpropyleneurea (dmpu) solvated lanthanoid(III) ions have been studied in dmpu solution (La-Nd, Sm-Lu) and in solid iodide salts (La-Nd, Sm, Gd-Lu) by extended X-ray absorption fine structure (EXAFS), and single crystal X-ray diffraction (La, Pr, Nd, Gd, Tb, Er, Yb, and Lu); the EXAFS studies were performed on both K and L(III) absorption edges. Because of the space-demanding properties of dmpu upon coordination, dmpu solvated metal ions often show coordination numbers lower than those found in corresponding hydrates and solvates of oxygen donor solvents without steric requirements beyond the size of the donor atom. All lanthanoid(III) ions are seven-coordinate in solution, except lutetium(III) which is six-coordinated in regular octahedral fashion, whereas in the solid iodide salts the dmpu solvated lanthanoid(III) ions are all six-coordinate in regular octahedral fashion, A comparison of Ln-O bond lengths in a large number of lanthanoid(III) complexes with neutral oxygen donor ligands and different configurations shows that the metal ion-oxygen distance is specific for each coordination number with a narrow bond distance distribution. This also shows that the radius of the coordinated oxygen atom in these compounds can be assumed to be 1.34 angstrom as proposed for coordinated water, while for ethers such as tetrahydrofuran (thf) it is somewhat larger. Using this atomic radius of oxygen in coordinated water molecules, we have calculated the ionic radii of the lanthanoid(III) ions in four- to nine-coordination and evaluated using the bond lengths reported for homo- and heteroleptic complexes in oxygen donor solvates in solution and solid state. This yields new and revised ionic radii which in some instances are significantly different from the ionic radii normally referenced in the literature, including interpolated values for the elusive promethium(III) ion
Hydration of Lanthanoid(III) Ions in Aqueous Solution and Crystalline Hydrates Studied by EXAFS Spectroscopy and Crystallography: The Myth of the Gadolinium Break
No full textThe structures of the hydrated lanthanoid(III) ions including lanthanum(III) have been characterized in aqueous solution and in the solid trifluoromethanesulfonate salts by extended X-ray absorption fine structure (EXAFS) spectroscopy. At ambient temperature the water oxygen atoms appear as a tricapped trigonal prism around the lanthanoid(III) ions in the solid nonaaqualanthanoid(III) trifluoromethanesulfonates. Water deficiency in the capping positions for the smallest ions starts at Ho and increases with increasing atomic number in the [Ln(H2O)(9-x)] (CF3SO3)(3) compounds with x = 0.8 at Lu. The crystal structures of [Ho(H2O)(8.91)](CF3SO3)(3) and [Lu(H2O)(8.2)](CF3SO3)(3) were re-determined by X-ray crystallography at room temperature, and the latter also at 100 K after a phase-transition at about 190 K. The very similar Ln K- and L-3-edge EXAFS spectra of each solid compound and its aqueous solution indicate indistinguishable structures of the hydrated lanthanoid(III) ions in aqueous solution and in the hydrated trifluoromethanesulfonate salt. The mean Ln-O bond lengths obtained from the EXAFS spectra for the largest ions, La-Nd, agree with estimates from the tabulated ionic radii for nine-fold coordination but become shorter than expected starting at samarium. The deviation increases gradually with increasing atomic number, reaches the mean Ln-O bond length expected for eightfold coordination at Ho, and increases further for the smallest lanthanoid(III) ions, Er-Lu, which have an increasing water deficit. The low-temperature crystal structure of [Lu(H2O)(8.2)](CF3SO3)(3) shows one strongly bound capping water molecule (Lu-O 2.395(4) angstrom) and two more distant capping sites corresponding to Lu-O at 2.56(1) angstrom, with occupancy factors of 0.58(1) and 0.59(1). There is no indication of a sudden change in hydration number, as proposed in the "gadolinium break" hypothesis
X-ray Absorption Fine Structure Spectroscopic Studies of Octakis(DMSO)lanthanoid(III) Complexes in Solution and in the Solid Iodides
No full textOctakis(DMSO)lanthanoid(III) iodides (DMSO = dimethylsulfoxide), [Ln(OS(CH3)(2))(8)]I-3, of most lanthanoid(III) ions in the series from La to Lu have been studied in the solid state and in DMSO solution by extended X-ray absorption fine structure (EXAFS) spectroscopy. L-3-edge and also some K-edge spectra were recorded, which provided mean Ln-O bond distances for the octakis(DMSO)lanthanoid(III) complexes. The agreement with the average of the Ln-O bond distances obtained in a separate study by X-ray crystallography was quite satisfactory. The crystalline octakis(DMSO)lanthanoid(III) iodide salts have a fairly broad distribution of Ln-O bond distances, ca. 0.1 angstrom, with a few disordered DMSO ligands. Their EXAFS spectra are in excellent agreement with [hose obtained for the solvated lanthanoid(III) ions in DMSO solution, both of which show slightly asymmetric distributions of the Ln-O bond distances. Hence, all lanthanoid(III) ions are present as octakis(DMSO)lanthanoid(ill) complexes in DMSO solution, with the mean Ln-O distances centered at 2.50 (La), 2.45 (Pr), 2.43 (Nd), 2.41 (Sm), 2.40 (Eu), 2.39 (Gd), 2.37 (Tb), 2.36 (Dy), 2.34 (Ho), 2.33 (Er), 2.31 (Tm), and 2.29 angstrom (Lu). This decrease in the Ln-O bond distances is larger than expected from the previously established ionic radii for octa-coordination. This indicates increasing polarization of the Ln(III)-O(DMSO) bonds with increasing atomic number. However, the S(1s) electron transition energies in the sulfur K-edge X-ray absorption near-edge structure (XANES) spectra, probing the unoccupied molecular orbitals of lowest energy of the DMSO ligands for the [Ln(OS(CH3)(2))(8)](3+) complexes, change only insignificantly from Ln = La to Lu. This indicates that there is no appreciable change in the sigma-contribution to the S-O bond, probably due to a corresponding increase in the contribution from the sulfur lone pair to the bonding
High-Energy X-ray Absorption Spectroscopy: A New Tool for Structural Investigations of Lanthanoids and Third-Row Transition Elements
No full textThis is the first systematic study exploring the potential of high-energy EXAFS as a structural tool for lanthanoids and third-row transition elements. The K-edge X-ray absorption spectra of the hydrated lanthanoid(III) ions both in aqueous solution and in solid trifluoromethanesulfonate salts have been studied. The K-edges of lanthanoids cover the energy range from 38 (La) to 65 keV (Lu), while the corresponding energy range for the L,edges is 5.5 (La) to 9.2 keV (Lu). We show that the large widths of the core-hole states do not appreciably reduce the potential structural information in the high-energy K-edge EXAFS data. Moreover, for lanthanoid compounds, more accurate structural parameters are obtained from analysis of K-edge than from L-3-edge EXAFS data. The main reasons are the much wider k range available and the absence of double-electron transitions, especially for the lighter lanthanoids. A comparative K- and L-3-edge EXAFS data analysis of nonahydrated crystalline neodymium(III) trifluoromethanesulfonate demonstrates the clear advantages of K-edge analysis over conventionally performed studies at the L-3-absorption edge for structural investigations of lanthanoid and third-row transition metal compounds. The coordination chemistry of the hydrated lanthanoid(III) ions in aqueous solution and solid trifluoromethanesulfonate salts, based on the results of both the K- and L-3-edge EXAFS data, is thoroughly discussed in the next paper in this serie
Quantitative Analysis of Deconvolved X-ray Absorption Near-Edge Structure Spectra: A Tool To Push the Limits of the X-ray Absorption Spectroscopy Technique.
No full textA deconvolution procedure has been applied to K-edge X-ray absorption near-edge structure (XANES) spectra of lanthanoid-containing solid systems, namely, hexakis(dmpu)praseodymium(III) and -gadolinium(III) iodide. The K-edges of lanthanoids cover the energy range 38 (La)-65 (Lu) keV, and the large widths of the core-hole states lead to broadening of spectral features, reducing the content of structural information that can be extracted from the raw X-ray absorption spectra. Here, we demonstrate that deconvolution procedures allow one to remove most of the instrumental and core-hole lifetime broadening in the K-edge XANES spectra of lanthanoid compounds, highlighting structural features that are lost in the raw data. We show that quantitative analysis of the deconvolved K-edge XANES spectra can be profitably used to gain a complete local structural characterization of lanthanoid-containing systems not only for the nearest neighbor atoms but also for higher-distance coordination shells
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