Peacock-Weakley complexes

Numerous reports of other examples of 1 2 Peacock-Weakley complexes are summarized in Table 5. Whereas some of these species have subsequently been confirmed by structural crystallography, many of the cited references report only non structure-specific data such as elemental analyses, IR spectra, magnetic moments, and electrochemistry. 

TABLE 5 Reported examples of 1 2 Peacock-Weakley complexes, [RL2] ... 

TABLE 7 Some reported conditional formation constants for Peacock-Weakley complexes... 

The Peacock-Weakley complexes [R(PWn039)2]11 and [R(P2Wi706i)2]17 are reported to give higher luminescence intensities than the corresponding de-catungsto complexes when R = Nd or Yb, but no energy transfer to the rare-earth... 

Several rare-earth Peacock-Weakley complexes with [SiWn039]8- ligands have been investigated for catalysis of methanol conversion and showed enhanced activity over H4SiWi204o (Wu et al., 1985,1986). 

In addition to the 12-molybdocerate complexes described in Section 2.1, and the Peacock-Weakley analogs listed in Table 4, there have been other attempts to synthesize rare-earth complexes of molybdates. In view of the inadequacies of 95Mo-NMR caused by low sensitivity and quadrupolar relaxation, and the ambiguities of other spectroscopic methods, it has so far been impossible to confirm whether those compounds that reveal discrete polyoxoanions in crystal structure analysis yield solutions that retain the same structures. 

Peacock-Weakley anions, exemplified by a-[PWu039] and a2-[P2W 706i]. Both of these are stable in aqueous solution and this stability allows the straightforward determination of conditional formation constants. Pi and P2 for the 1 1 and 1 2 complexes respectively (see Table 1 for examples)... 

The first systematic studies of polyoxometalate—rare-earth complexes were published in 1971 (Peacock and Weakley, 1971a, 1971b). Two classes of polytungstate complexes were described and these can now be seen to have common structural features. The complexes of Y, La, Ce(III and IV), Pr, Nd, Sm, Ho, Er, and Yb in which R W = 1 10 were readily formed by reaction of WO - with the appropriate rare-earth salt, but are stable only within the pH range 5.5-8.5. More recent 183W-NMR studies (Inoue et al., 2003) indicate that in solution the anions containing the heaviest R (Tm, Yb and Lu) are partially decomposed. 

Two isomers [al-P2Wi706i] ° and [a2-P2Wi706i] ° can be derived from the parent Wells-Dawson anion [a-P2Wi8062] by removal of a belt or cap W = Od unit, respectively. Complexes of RE ions with a lacunary [a-P2Wi706i] ° anion were first reported by Peacock and Weakley in 1971, which is now known as [RE(a2-P2Wi706i)2]" - The complex of the al isomer, [RE(al-P2Wi706i)]" , has also been prepared, although it could not be isolated. Until... 

The lacunary anions [PWnOsg] ", [SiWn039] " and (a2-) [P2Wi706i] °" were first shown to form complexes with a variety of lanthanide cations (Ln POM =1 1 and 1 2) by Peacock and Weakley in 1971.[41] At that time only the 1 2 complexes could be isolated, and the ai isomer of [P2Wi706i] ° had not been discovered. The first actinide (tetravalent Th, U) analogs of the Peacock-... 

Anions of type 2 above were first synthesized by Peacock and Weakley in 1971, and the first reports of crystal structures of such (1 2) complexes ([U (GeWu039)2] and... 

R.D. Peacock and T.J.R. Weakley, Heteropolytungstate complexes of the lanthanide elements. Part 1. 

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