Chapter 4 - Jacobs University

Chapter 9
Unpublished Results
9.3.5.2 Results and discussion
The structure of [{Hf(O 2 )(SiW 11 O 39 )} 2 ] 12- (25) (Figure 9.72) reveals that the novel polyanion
consists of two [α-SiW 11 O 39 ] 8- anions linked by {Hf 2 (O 2 ) 2 } 4+
group in a head-on fashion,
resulting in an assembly with C i symmetry. The Hf 4+
ion is located in an antiprismatic
coordination environment with eight oxygen atoms, four of them being connected to the
polyanion and other four being connected to the two peroxo oxygen groups. The BVS
calculation indicates that none the four oxygen atoms from the peroxo groups are protonated. We
performed TGA measurements on 25a (Figure 9.71) from room temperature to 900 °C which is
fully consistent with the formula of 25a provided above.
Figure 9.72 Polyhedral/ball and stick type structural representation of 25. Color scheme: Hf, Si and WO 6 units are
shown by light green, green and red respectively.
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