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For this the parent ion [
D
-P
2
W
18
O
62
]
6-
has to be converted into the defect complex [
D
-
P
2
W
17
O
61
]
10-
which afterwards can be substituted with an additional element and
extracted into organic media using Q
7
-Br following an analogous reaction procedure as
for the Keggin-POMs (for details see experimental section).
Figure 46
left: Ball and stick representation of the substituted Dawson cluster [
D
2
-P
2
W
17
O
61
ML]
10-
;
heteroatom phosphor (orange), addenda atoms tungsten (blue), oxygen (red), d-element M (grey),
additional ligand L e.g. water (green). right: Polyhedral representation with [WO
6
]-polyhedra (blue),
heteroatom phosphor (orange), oxygen (red) and highlighting of the square lacunary site with its four
main oxo-ligands.
In this work Co(II) and Fe(III) have been incorporated successfully into the Dawson
cluster with consecutive phase transfer into toluene using Q
7
-Br. Both products
(Q
7
)
8
[
D
-P
2
W
17
O
61
Co(H
2
O)] and (Q
7
)
7
[
D
-P
2
W
17
O
61
Fe(H
2
O)] show clearly higher viscosity
compared to the synthesized Keggin ILs and are obtained as gummy solids at room
temperature. This finding may be rationalized at hand of the size and charge of the
Dawson cluster. It has a prolate ellipsoidal shape (so called prolate spheroid) in which
the polar axis is greater than the equatorial diameter. Its dimensions are ca.
12.2 Å x 10.3 Å x 10.3 Å corresponding to a volume of ca. 680 Å
3
. The Keggin anion has
dimensions of ca. 8.2 Å x 10.3 Å x 10.3 Å and thus a volume of ca. 455 Å
3
. In the
following Table 10 the average volume charge densities are compared calculated
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