Chapter 4 - Jacobs University

Chapter 3 The Wheel-Shaped Cu 20
3.4 Results and discussion
3.4.1 Synthesis and structure
Polyanion [Cu 20 Cl(OH) 24 (H 2 O) 12 (P 8 W 48 O 184 )] 25- (1) (Figures 3.2 - 3.4) crystallized as a
mixed potassium-sodium salt K 12 Li 13 [Cu 20 Cl(OH) 24 (H 2 O) 12( P 8 W 48 O 184 )]·22H 2 O(1a) which
crystallized in the tetragonal space group I4/m. As a result the asymmetric unit of 1 includes only
6 tungsten and 3 copper atoms (Figure 3.5).
The title polyanion 1 is unprecedented in structure, size and composition. This
supramolecular assembly represents the first transition metal substituted derivative of
[H 7 P 8 W 48 O 184 ] 33- and it incorporates more paramagnetic ions than any other polyoxometalate
known to date. [12a,b,16] The structure of the wheel-shaped [H 7 P 8 W 48 O 184 ] 33- precursor is
maintained in 1 and the cavity has been filled with a highly symmetrical copper-hydroxo cluster
(Figures 3.2,3.3,3.6). This emphasizes that the template effect plays an important role during
formation of 1. We have shown (in disagreement with Tézé and Contant) that the oxo-groups in
the cavity of the tungstophosphate precursor [H 7 P 8 W 48 O 184 ] 33- actually do interact with transition
metal ions in aqueous medium, but some heating is required (Exp. Sect.). Therefore,
[H 7 P 8 W 48 O 184 ] 33- can indeed be considered as a superlacunary polyanion precursor and we
expect that other transition metal ions besides Cu 2+ can also be incorporated.
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