Synthesis and Structural Characterization of ... - Jacobs University

Chapter 3
Unpublished Results
Polyanions 15–17 consist of two SbW 9 subunits linked by two tungsten ions forming the
Sb 2 W 20 unit, which is coordinated to an external lanthanide and tungsten ion, leading to a
structure with idealized C s symmetry (see Figure 3.29). This unique, external tungsten ion is
six-coordinated, whereas the lanthanide ion is seven-coordinated in a pentagonal-bipyramidal
fashion.
Figure 3.29. Polyhedral (left) and ball-and-stick (right) representations of
[Ln(H 2 O) 3 Sb 2 W 21 O 72 (OH))] 10− (Ln = Yb (15), Lu(16), Y(17)). The color code is as follows:
WO 6 octahedra (red), rotated WO 6 octahedra (yellow), W (black), Sb (green), Ln (blue), H 2 O
(pink), O (red), and OH (gray).
It is noteworthy that because of the high charge of the intermediate [Sb 2 W 20 O 70 ] 14−
Sb 2 W 20 , it tends to be stabilized by cations to form M 2 Sb 2 W 20 or to undergo further
condensation reactions to from Sb 2 W 22 polyanion, depending on the pH of the solution. 5
Interestingly, this intermediate Sb 2 W 20 unit in the presence of lanthanide ions and a lower pH
value (~ 3) tends to undergo further condensation reaction forming a novel unit Sb 2 W 21 which
coordinates to one lanthanide ion forming polyanions 15–17. Furthermore, this structurally
unique fac-WO 6 octahedron has one monoprotonated and two nonprotonated terminal oxo
ligands, and hence does not violate the Lipscomb rule. 11
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