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3.4.2. Ionic liquids based on the dilacunary {SiW
10
}
All clusters discussed so far featured one lacunary position to bind additional d-metals,
to which the cluster behaves as pentadentate ligand. This leaves only one single
coordination position free for performing chemical reactions. For many reactions it
would however be beneficial or even necessary to provide more than one binding
position at which the reagent and substrate could be brought into close proximity for a
reaction, e.g. CO-insertions or cross-coupling reactions. Aiming at improved possibilities
for cluster based catalytic reactions in the ionic liquid medium it was indented to
synthesize the dilacunary {
J
-SiW
10
}, functionalize it with a d-heterometal and obtain it
as a POM-IL. The {
J
-SiW
10
} is synthesized by increasing the pH of an aqueous solution of
the monolacunary K
8
[
E
-SiW
11
O
39
]
ڄ
14H
2
O to pH
=
9.1 with K
2
CO
3
and precipitate the
product after exactly 16 minutes.
[56]
This procedure leads to the formation of one
additional void adjacent to the lacunary position of the starting material creating a
rectangular lacuna with four main oxo-ligands at the edges (see Figure 47 right part).
The lacuna can accommodate two heterometals. For experimental purposes Cu(II) was
applied and 2.1 eq. of CuCl
2
ڄ
2H
2
O added following a similar reaction procedure as for
the {SiW
11
} clusters. For details see the experimental part.
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