Michaela Dankova | PubMed Health

PubMed2002

Lanthanide complexes of [alpha-2-P2W17O61]10-: solid state and solution studies.

We have isolated the 1:1 Ln:[alpha-2-P2W17O61]10- complexes for a series of lanthanides. The single-crystal X-ray structure of the Eu3+ analogue reveals two identical [Eu(H2O)3(alpha-2-P2W17O61)]7- moieties connected through two Eu-O-W bonds, one from each polyoxometalate unit. An inversion center relates the two polyoxometalate units. The Eu(III) ion is substituted for a [WO]4+ unit in the "cap" region of the tungsten-oxygen framework of the parent Wells-Dawson ion. The point group of the dimeric molecule is Ci. The extended structure is composed of the [Eu(H2O)3(alpha-2-P2W17O61)]214- anions linked together by surface-bound potassium cations. The space group is P, a = 12.7214(5) A, b = 14.7402(7) A, c = 22.6724(9) A, alpha = 71.550(3), beta = 84.019(3)degrees, gamma = 74.383(3), V = 3883.2(3) A3, Z = 1. The solution studies, including 183W NMR spectroscopy and luminescence lifetime measurements, show that the molecules dissociate in solution to form monomeric [Ln(H2O)4(alpha-2-P2W17O61)]7- species.

Chemical Phenomena↗

PubMed1999

Lanthanide Complexes of the alpha-1 Isomer of the [P(2)W(17)O(61)](10-) Heteropolytungstate: Preparation, Stoichiometry, and Structural Characterization by (183)W and (31)P NMR Spectroscopy and Europium(III) Luminescence Spectroscopy.

The alpha-1 and alpha-2 [P(2)W(17)O(61)](10)(-) isomers, derivatives of the Wells-Dawson molecule, [alpha-P(2)W(18)O(62)](6)(-), may be useful ligands for stabilizing high-valent metal ions and lanthanides and actinides. However, the potential utility of the [alpha1-P(2)W(17)O(61)](10)(-) ligand has not been realized. Specifically, for the lanthanides, the stoichiometry, structure, and purity of the lanthanide complexes of the [alpha1-P(2)W(17)O(61)](10)(-) isomer are ambiguous. We have prepared lanthanide (Ln) complexes of the [alpha1-P(2)W(17)O(61)](10)(-) isomer in >/=98% isomeric purity, according to (31)P NMR data. (183)W NMR data clearly showed, for the first time, that the C(1) symmetry of the [alpha1-P(2)W(17)O(61)](10)(-) lanthanide complexes was maintained in solution. We determined the stoichiometry of the lanthanide complexes of the [alpha1-P(2)W(17)O(61)](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:[alpha1-P(2)W(17)O(61)](10)(-) ratio. The (31)P 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(alpha1-P(2)W(17)O(61))](7)(-) complex showed >/=98% isomeric purity and the C(1) symmetry required for a derivative of [alpha1-P(2)W(17)O(61)](10)(-). Also the tetrabutylammonium cation stabilized the [Lu(alpha1-P(2)W(17)O(61))](7)(-) complex; a mixed tetrabutylammonium, lithium salt was stable in water for weeks according to (31)P NMR spectroscopy.

Journal Article↗