| Abstract
| - Octakis(DMSO)lanthanoid(III) iodides (DMSO = dimethylsulfoxide), [Ln(OS(CH3)2)8]I3, of most lanthanoid(III) ionsin the series from La to Lu have been studied in the solid state and in DMSO solution by extended X-ray absorptionfine structure (EXAFS) spectroscopy. L3-edge and also some K-edge spectra were recorded, which provided meanLn−O bond distances for the octakis(DMSO)lanthanoid(III) complexes. The agreement with the average of theLn−O bond distances obtained in a separate study by X-ray crystallography was quite satisfactory. The crystallineoctakis(DMSO)lanthanoid(III) iodide salts have a fairly broad distribution of Ln−O bond distances, ca. 0.1 Å, witha few disordered DMSO ligands. Their EXAFS spectra are in excellent agreement with those obtained for thesolvated lanthanoid(III) ions in DMSO solution, both of which show slightly asymmetric distributions of the Ln−Obond distances. Hence, all lanthanoid(III) ions are present as octakis(DMSO)lanthanoid(III) complexes in DMSOsolution, 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 Å (Lu). This decrease in the Ln−O bonddistances is larger than expected from the previously established ionic radii for octa-coordination. This indicatesincreasing polarization of the LnIII−O(DMSO) bonds with increasing atomic number. However, the S(1s) electrontransition energies in the sulfur K-edge X-ray absorption near-edge structure (XANES) spectra, probing the unoccupiedmolecular orbitals of lowest energy of the DMSO ligands for the [Ln(OS(CH3)2)8]3+ complexes, change onlyinsignificantly from Ln = La to Lu. This indicates that there is no appreciable change in the σ-contribution to theS−O bond, probably due to a corresponding increase in the contribution from the sulfur lone pair to the bonding.
- EXAFS L3- and high-energy K-edge spectra show similar octakis(DMSO)lanthanoid(III) complexes in DMSO solution as in the solid iodides. For the smaller lanthanoid(III) ions, the deviation of the mean Ln−O bond distances (symbols) increases from those derived from ionic radii (solid lines) without coordination number change. Sulfur K-edge XANES spectra probe changes in σ-contributions to the S−O bonds by metal ion−oxygen bonding of the DMSO ligands.
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