Synthesis and Structural Characterization of ... - Jacobs University

Chapter 3
Unpublished Results
3.B.2. Mono‐ and Di‐Lanthanide Derivatives of Tungstoantimonate(III)
3.B.2.1. Introduction
Polyoxometalates (POMs) represent a class of discrete structurally and chemically diverse
nanosized metal-oxygen molecular anions of early transition metals (groups V and VI) in their
high oxidation states. 1
However, recently, polyoxopalladates and –aurates have been
synthesized and structurally characterized by our group. 2 Due to the large versatility of POMs
gives rise to various applications in fields such as catalysis, medicine, analytical chemistry,
and material science. 1 Although the first synthetic POM is known since 1826, the mechanism
of POM formation is still not completely understood and is often described as a self-assembly
process. POMs are usually formed via condensation of mono nuclear metalate ions in
acidified solutions (usually aqueous). 1
Lacunary POM precursors containing a hetero group with a lone pair of electrons (e. g.
As III , Sb III ) are of particular interest, because the lone pair does not allow the closed Keggin
unit to form, resulting in a very different reactivity compared to lacunary POMs with a
tetrahedral hetero group. The trilacunary precursor [B-α-SbW 9 O 33 ] 9− (SbW 9 ) is a member of
this subclass. This SbW 9 anion was first reported by Tourné et al. in 1973. 3 It is stable at pH
7.7 – 9 in B-SbW 9 type and does not react with tungstate to give Sb III W 11 . However solution
of SbW 9 anions react with divalent metal ions to give [M 3 (B-α-SbW 9 O 33 ) 2 ] 12− (M = Cu, Ni,
Zn, etc.). 3
Since then, more metal ions derivatives of the SbW 9 polyanion have been
synthesized and reported. 4
In 1997, Krebs et al. reported the [Sb 2 W 22 O 74 (OH) 2 ] 12−
(Sb 2 W 22 ) polyanion which
composed of two [B-ß-SbW 9 O 33 ] 9− units linked through four WO 6 fragments (see Figure
3.26). Since, one triad (W 3 O 13 ), (yellow in Figure 3.26) in the [B-α-SbW 9 O 33 ] 9− unit has been
rotated by 60˚ along the Sb–O bond vector. Furthermore, it has an inversion center and the
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