Coordination of rare-earth-elements in complexes with monovacant Wells-Dawson polyoxoanions: x-ray crystallography, XAFS, and luminescence spectroscopy.
The {alpha}-1 and {alpha}-2 isomers of the monovacant Wells-Dawson heteropolyoxoanion [P{sub 2}W{sub 17}O{sub 61}]{sup 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{sub 2}W{sub 17}O{sub 61}]{sup 10-} and {alpha}-2-[P{sub 2}W{sub 17}O{sub 61}]{sup 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{sub 2}W{sub 17}O{sub 61})]{sup 7-} and [Ln({alpha}-2-X{sub 2}W{sub 17}O{sub 61}){sub 2}]{sup 17-} (for Ln {triple_bond} Sm, Eu, Lu; X {triple_bond} P, As). The crystal and molecular structures of [(H{sub 2}O){sub 4}Lu({alpha}-1-P{sub 2}W{sub 17}O{sub 61})]{sup 7-} (1) and [Lu({alpha}-2-P{sub 2}W{sub 17}O{sub 61}){sub 2}]{sup 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{sub 2}W{sub 17}O{sub 61}]{sup 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{sub 2}O){sub 4}Ln({alpha}-1-P{sub 2}W{sub 17}O{sub 61})]{sup 7-}. This structure (1) is the first of its kind for any metal complex of {alpha}-1-[P{sub 2}W{sub 17}O{sub 61}]{sup 10-}, and the data indicate that the general stoichiometry [(H{sub 2}O){sub 4}Ln({alpha}-1-P{sub 2}W{sub 17}O{sub 61})]{sup 7-} is maintained throughout the lanthanide series. For the 1:2 stoichiometric Ln/{alpha}-2-[X{sub 2}W{sub 17}O{sub 61}]{sup 10-} complexes, no water molecules are in the Ln-O{sub 8} coordination sphere. The Ln ions are bound to eight O atoms -- four from each of two heteropolyanions -- as [Ln({alpha}-2-X{sub 2}W{sub 17}O{sub 61}){sub 2}]{sup 17-}. The average Ln-O interatomic distances decrease across the lanthanide series, consistent with the decreasing Ln ionic radius.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- National Science Foundation (NSF); National Institutes of Health (NIH)
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 943198
- Report Number(s):
- ANL/CHM/JA-38206; INOCAJ; TRN: US0903012
- Journal Information:
- Inorg. Chem., Vol. 40, Issue 2001; ISSN 0020-1669
- Country of Publication:
- United States
- Language:
- ENGLISH
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