Lanthanide Complexes of the α-1 Isomer of the [P2W17O61]10- Heteropolytungstate:  Preparation, Stoichiometry, and Structural Characterization by 183W and 31P NMR Spectroscopy and Europium(III) Luminescence Spectroscopy

• Published in: Inorganic chemistry 1999-03, Vol.38 (6), p.1042-1053
• Main Authors: Bartis, Judit, Dankova, Michaela, Lessmann, Jeremy J, Luo, Qun-Hui, Horrocks, William DeW, Francesconi, Lynn C
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic980384i

The α-1 and α-2 [P2W17O61]10- isomers, derivatives of the Wells−Dawson molecule, [α-P2W18O62]6-, may be useful ligands for stabilizing high-valent metal ions and lanthanides and actinides. However, the potential utility of the [α1-P2W17O61]10- ligand has not been realized. Specifically, for the lanthanides, the stoichiometry, structure, and purity of the lanthanide complexes of the [α1-P2W17O61]10- isomer are ambiguous. We have prepared lanthanide (Ln) complexes of the [α1-P2W17O61]10- isomer in ≥98% isomeric purity, according to 31P NMR data. 183W NMR data clearly showed, for the first time, that the C 1 symmetry of the [α1-P2W17O61]10- lanthanide complexes was maintained in solution. We determined the stoichiometry of the lanthanide complexes of the [α1-P2W17O61]10- isomer in solution by two different methods:  a complexometric titration method and excited state lifetime measurements and luminescence titrations for the europium(III) analogue. All experiments show a 1:1 Ln:[α1-P2W17O61]10- ratio. The 31P NMR data showed that the lanthanides with smaller ionic radii (higher charge-size ratio) form stable complexes, even surviving crystallization from hot water. On the other hand, the lanthanum analogues were not stable in solutions of high lithium content. The tetrabutylammonium salt of the [Lu(α1-P2W17O61)]7- complex showed ≥98% isomeric purity and the C 1 symmetry required for a derivative of [α1-P2W17O61]10-. Also the tetrabutylammonium cation stabilized the [Lu(α1-P2W17O61)]7- complex; a mixed tetrabutylammonium, lithium salt was stable in water for weeks according to 31P NMR spectroscopy.