PdII and PtII Metal-Directed Self-Assembly of Supramolecular Structures Based on N-Monoalkyl-4,4¢-Bipyridinium Derivatives - Molecular Self-Assembly: Advances and Applications - page 362

between the centroid defined by the atoms of the long side of the
rectangle and the plane of pyrene is 3.40 Å, exactly the optimum
calculated distance for systems held by face-to-face π-stacking
interactions. The long side of the metallocycle measures 14.75 Å,
slightly longer than the calculated one. The plane containing the
pyrene molecule is inclined by 70 with respect to the equatorial

plane of the metallocycle defined by its four corners, while the axis
defined by pyrene protons H2 and H7 forms an angle of 30

°

with
the same plane. Another consequence is the decrease on the torsion
angle in the bipyridinium moiety from 31

°

°

to 25

°

as a result of the

π - π stacking interactions.

Figure 11.6 View of the crystal structure of inclusion complex

pyrene . Color-labeling scheme as in Fig. 11.5.

Hydrogen atoms from the metallocycle, solvent molecules,
and counter ions have been omitted for clarity.

⊂ M4a

·6NO 3

11.4.2 Inclusion Complexes with 1:2 Stoichiometry

As described earlier, expansion of one of the metallocycle sides
allows the complexation of larger substrates. Conversely, extension
of the other side makes the cavity size large enough (ca. 10.4 Å) to
receive two molecules of substrate (Fig. 11.3). Thus, addition of one
equiv. of (en)Pd(NO (10 mM) at room

temperature gives rise to the formation of metallocycle

) to a D O solution of L5 ·2NO

3 2 2 3

.
The addition of two equiv. of hydroquinone to a 5 mM solution
of metallocycle

M5a ·8NO 3

in water produced a pale red coloration.
This is related to the presence of an intermolecular charge transfer
absorption band centered at 439 nm [27]. The crystal structure

M5a ·8NO 3