Chapter 4 - Jacobs University

Chapter 5
Organoruthenium POM
The four organoruthenium units in 3 are grafted near the rim of the central cavity of P 8 W 48 with
the hydrophobic p-cymene groups protruding away from the hydrophilic polyanion (Figure 5.5).
This allows for a potassium ion to be accommodated in each of the two opposite hinge-areas of
3. Interestingly, two of the waters coordinated to Ru point toward the inside of the cavity of 3
and the other two point toward the outside of the cyclic polyanion.
The ruthenium centers in 3 bind to what appear to be the most reactive and sterically
accessible oxygens of P 8 W 48 . Also in our Cu 2+ containing derivative
[Cu 20 Cl(OH) 24 (H 2 O) 12 (P 8 W 48 O 184 )] 25− the central {Cu 20 (OH) 24 } 16+ cluster interacts with the same
type of polyanion oxygens, but with all 16 equivalent sites on the inner surface of P 8 W 48 at the
same time.
At first sight, it seems that steric constraints allow only four rather than the expected eight
bulky organoruthenium groups to be accommodated in the cavity of P 8 W 48 . Interestingly, those
four groups are all in the same plane, bound on opposite sides of the inner cavity, which
indicates that binding cooperativity is at work during formation of 3 (vide infra). The remaining
four binding sites in 3 are occupied by two potassium ions and, very unexpectedly, also by two
additional tungsten atoms (Figure 5.3 and 5.4).However, these inversion symmetry related
potassium and tungsten sites exhibit only 50% occupancy, indicating crystallographic disorder.
This means that in a given polyanion 3 only two of the four positions are actually occupied.
There are no geometrical or steric constraints, therefore allowing for all three possible occupancy
scenarios
The presence of one extra equivalent of tungsten in 3 is important, as it leads to the first
example of a P 8 W 49 framework. Furthermore, the coordination environment of this additional
98