Photophysics and Photochemistry of Molecular Recognition and Sensing with Metal-Directed Macrocyclic Systems - Molecular Self-Assembly: Advances and Applications - page 319

methanol to give corresponding inclusion complexes [74]. For
example, a significant upfield shift of

∼

0.11 ppm for ortho protons and

0.2 ppm for protons of 1,5-dihydroxynaphthalene was observed

as a function of concentration in the

meta

1

(see
Fig. 10.4). Thus, the rational design of efficient hosts for molecular
recognition involves the introduction of specific recognition sites
into the assembly. Stang

H NMR titration with 21

have designed molecular squares with
Lewis base receptor sites, which show a variety of metal-binding
capability and geometrical predictability. X-ray crystallography of
the Lewis acid/base host

et al.

−

with phenazine
provided new insight into molecular recognition design [75]. There
are several interesting structural features evident for this complex.
The overall geometry of the perimeter for this complex is almost
planar with the guest phenazine oriented nearly orthogonal to the
Pt

guest molecular square 23

−

2+

−

Pt Pt plane.

∑

Figure 10.4 Plot of change in chemical shifts of the )

protons of guest molecule as a function of concentration of
host

ortho ( ) and meta (



21 . Reproduced with permission from Ref. [74].

π

The -complexed silver atoms are located in a pseudo trans

−

2+

−

arrangement with respect to the Pt -

symmetric relationship. Interestingly, the acetylene moieties in the
backbone of the molecular square

Pt Pt plane, resulting in a C

i

23 interact with two equivalents

of silver triflate to give a host , with considerable

stability in solution. Further, the metallacylic square

−

guest complex, 24

serves as a
receptor to bind Lewis basic guests with the appropriate size being
achieved through the coordination of silver cations via “

24

π

-tweezer