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resulted in a clear evolution of the
voltammogram (Fig. 10.8). The redox peak of the Fe
to a solution of compound
52
III
II
/Fe
couple
shifted to 0.78 V, the presence of Mg
2+
being thus evident by an
unexpected cathodic shift of
240 mV. Further addition of Mg(NO
)
3
2
(until 5 eq.) had no significant effect, indicative of the formation of
the stable 1:2 mole ratio. The unusual cathodic redox-potential shift
upon cation binding is opposed to an intuitive anodic shift, and is
ascribed to the electronic reorganization of the metallacycle.
Figure 10.8
Differential pulse voltammetry for complex
52
in solution (a)
2+
2+
52
, (b)
52
:1 eq. of Mg
, and (c)
50
:2 eq. of Mg
. Reproduced
with permission from Ref. [93].
based supramolecules were found to be
highly luminescent as well as redox-active materials [94]. The
metallasquare
Perylene bisimide
53
displayed two reductive waves (
E
=
1.01 and
1/2
+
), which were attributed to the monoanionic and
dianionic perylene bisimide species. Both reductions are shifted
by about
1.14 V vs. Fc/Fc
90 mV with respect to the bridging perylene
bisimide ligand. Notably, it was possible to reversibly oxidize
perylene bisimide units in
70 to
= +0.93 V. However,
the free ligand was irreversibly oxidized and adsorbed onto the
platinum electrode. This is attributed to the coordination of the
pyridine nitrogen to platinum, thereby blocking the nitrogen lone
pair in a way that the metallacycle is no longer susceptible to
adsorption and facile oxidation. The perylene bisimide scaffold
incorporates the redox-active ferrocene units, and this makes the
three-dimensional metallacyclic superstructure
53
at potential
E
1/2
more versatile
toward electrochemical behavior [95]. The introduction of ferrocene
in the molecule is an excellent choice for probing electron-transfer
54
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