Chapter 4 - Jacobs University

Chapter 9
Unpublished Results
9.2.1.2 Results and discussion
We propose a structure of tetramer type yttrium polyoxometalate [Cs{Y(B-a-AsW 9 O 33 )} 4 ] 23-
(15), which is isostructural to the tetramer POMs of yttrium reported by Francesconi in 2001.
The compound 15a was fully characterized in the solid state by single-crystal XRD, TGA-DSC,
and IR as well as in solution by 89 Y NMR. The metal framework contains symmetrical four Y 3+
ions bridging four [B-a-AsW 9 O 33 ] 9- units and encapsulating central cesium atom where cesium
act as a template ion. The polyanion 15 resembles a pin-wheel configuration, where the central
cesium atom has square prismatic geometry. Each yttrium ion is connected to four oxygens on a
rectangular face of [B-a-AsW 9 O 33 ] 9- with bond distances ranging from 2.32 Å to 2.44 Å and
bond angles ranging from 83.89° to 111.51° with adjacent oxygen atoms. The yttrium ion
coordinates with two terminal oxygen atoms of bridging [B-a-AsW 9 O 33 ] 9- unit with bond
distances of 2.30 and 2.32 Å respectively and bond angle of 70.13° and the remaining two
coordination sites are filled by two water molecules at a distance of 2.41 Å. The Y 3+ has a
slightly distorted square antiprismatic geometry (Figure 9.26).
We performed bond valence sum (BVS) calculations of 15 which suggest that all oxygen atoms
are nonprotonated. So, the charge on the compound is -24 which is balanced equally by cesium
and sodium ions in the solid state. We also performed TGA measurements on 15a from room
temperature to 900 °C in order to confirm the number of crystal waters (Figure 9.25).
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