Chapter 4 - Jacobs University

Chapter 6
U-peroxo-Polyoxometalate
groups which actually appear to be in equilibrium with “free” phosphate as seen by the singlet
(without any satellites) at 0.4 ppm. Indeed, addition of extra phosphate to the solution results in
an increase of the signal at 0.4 ppm. The exchange of “free” and “bound” phosphate in 4 is slow
on the NMR timescale.
The two phosphate caps in 4 are bound via only two P-O(W) bridges each to the “P 6 W 36 ”
fragment (P-O(W) 1.43-1.47(2) 1.47(2) Å). The two remaining oxygens are terminal, and BVS
calculations 26 indicate that one of them (O1P7/O1P8) is actually a hydroxo group (P-O(H) 1.46-
1.47(3) Å). This hydroxo group is stabilized by a long interaction to K1/K4 (~2.8 Å). The
remaining terminal PO 4 oxygen is non-protonated (P-O 1.47(3) Å) and points away from the
polyanion ligand.
Figure 6.5 Room
temperature
CH 3 COOLi/CH 3 COOH at pH 4.0.
31 P NMR spectrum of 4a redissolved in 1M
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