title: Coordination of rare-earth elements in complexes with monovacant Wells-Dawson polyoxoanions.
abstract: The alpha-1 and alpha-2 isomers of the monovacant Wells-Dawson heteropolyoxoanion [P(2)W(17)O(61)](10-) are complexants of trivalent rare-earth (RE) ions and serve to stabilize otherwise reactive tetravalent lanthanide (Ln) and actinide (An) ions in aqueous solution. Aspects of the bonding of Ln ions with alpha-1-[P(2)W(17)O(61)](10-) and alpha-2-[P(2)W(17)O(61)](10-) were investigated to address issues of complex formation and stability. We present structural insights about the Ln(III) coordination environment and hydration in two types of stoichiometric complexes, [Ln(alpha-1-P(2)W(17)O(61))](7-) and [Ln(alpha-2-X(2)W(17)O(61))(2)](17-) (for Ln identical with Sm, Eu, Lu; X identical with P, As). The crystal and molecular structures of [(H(2)O)(4)Lu(alpha-1-P(2)W(17)O(61))](7-) (1) and [Lu(alpha-2-P(2)W(17)O(61))(2)](17-) (2) were solved and refined through use of single-crystal X-ray diffraction. The crystallographic results are supported with corresponding insights from XAFS (X-ray absorption fine structure) for a series of nine solid-state complexes as well as from optical luminescence spectroscopy of the Eu(III) analogues in aqueous solution. All the Ln ions are eight-coordinate with oxygen atoms in a square antiprism arrangement. For the 1:1 stoichiometric Ln/alpha-1-[P(2)W(17)O(61)](10-) complexes, the Ln ions are bound to four O atoms of the lacunary polyoxometalate framework in addition to four O atoms from solvent (water) molecules as [(H(2)O)(4)Ln(alpha-1-P(2)W(17)O(61))](7-). This structure (1) is the first of its kind for any metal complex of alpha-1-[P(2)W(17)O(61)](10-), and the data indicate that the general stoichiometry [(H(2)O)(4)Ln(alpha-1-P(2)W(17)O(61))](7-) is maintained throughout the lanthanide series. For the 1:2 stoichiometric Ln/alpha-2-[X(2)W(17)O(61)](10-) complexes, no water molecules are in the Ln-O(8) coordination sphere. The Ln ions are bound to eight O atoms-four from each of two heteropolyanions-as [Ln(alpha-2-X(2)W(17)O(61))(2)](17-). The average Ln-O interatomic distances decrease across the lanthanide series, consistent with the decreasing Ln ionic radius.
authors: Chemistry Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, Illinois 60439, USA.
authors: Q H
authors: QH
authors: Luo
authors: R C
authors: RC
authors: Howell
authors: M
authors: M
authors: Dankova
authors: J
authors: J
authors: Bartis
authors: C W
authors: CW
authors: Williams
authors: W D
authors: WD
authors: Horrocks
authors: V G
authors: VG
authors: Young
authors: A L
authors: AL
authors: Rheingold
authors: L C
authors: LC
authors: Francesconi
authors: M R
authors: MR
authors: Antonio
mesh_terms: D000838:Anions / Q000737:chemistry; D049449:Luminescence; D008674:Metals, Rare Earth / Q000737:chemistry*; D015394:Molecular Structure; D013053:Spectrophotometry; D017973:Tungsten Compounds / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D000838:Anions; D008674:Metals, Rare Earth; D017973:Tungsten Compounds