Chapter 4 - Jacobs University

Chapter 9
Unpublished Results
9.2.3.2 Results and discussion
The polyanion [{Y(CH 3 COO)SiW 11 O 39 } 2 ] 12- (17) (Figure 9.35) consists of two [a-SiW 11 O 39 ] 8-
anions linked by a [{(CH 3 COO)(H 2 O) 2 Y} 2 ] 4+ group in head to head fashion which results in a
dimeric compound with C 2h symmetry. The acetate molecules are bound to the Y 3+ ions in rather
unexpected fashion. The compound 17a was fully characterized in the solid state by singlecrystal
XRD, TGA-DSC, and IR as well as in solution by 1 H, 13 C, 89 Y and 183 WNMR. In this
polyanion, each Y 3+ ion is coordinated to 8 oxygen atoms. Out of these 8 oxygen atoms four
atoms are from the Keggin fragment. Three more oxygen atoms are part of acetate groups and
the remaining oxygen is from a water molecule. The ÐO-Y-O bond angle is 65.23° with the two
oxygen atoms from two different acetate groups while the ÐO-Y-O bond angle is 53.043° with
two oxygen atoms from same acetate group. The yttrium ions have bond distances of 2.42Å with
two bridging acetate oxygen atoms and 2.45 Å with the other acetate oxygen atoms, and bond
distances ranging from 2.26 to 2.32 Å with oxygen atoms from the Keggin fragments [a-
SiW 11 O 39 ] 8- . We performed TGA measurements on 17a (Figure 9.34) from room temperature to
900 °C which is fully consistent with the formula of 17a provided above.
187