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also in the sensing of nitroaromatics, which are presently used in the
preparation of chemical explosive materials.
9.2
2D Molecular Architectures Containing
Ethynyl Moiety: Molecular Rectangles
Among the various 2D architectures that have been mostly synthesized
in recent times the rectangle is a much less-known geometry for the
supramolecular assemblies. One of the most common approach that
can be applied for designing a rectangle is the three-component [4 +
2 + 2] self-assembly reaction of a 90
°
corner in combination with two
linear linkers of different lengths. Only few examples are known in
the literature where rhenium-based rectangles have been prepared
using this approach [19]. However, no success is known for Pt
II
or
II
metals using this design principle. The main disadvantage of this
approach is the lack of selectivity in the formation of the desired
rectangle because of the possibility of formation of a mixture of
squares of different sizes from the combination of 90
Pd
°
corners with
the individual linear linkers (Scheme 9.1).
Scheme 9.1
Possible cyclic products in [4 + 2 + 2] self-assembly of a 90
°
acceptor and two linear linkers of different lengths.
This problem can be overcome by designing a [2 + 2] self-
assembly reaction, in the lines of Stang and co-workers, employing a
molecular “clip” in conjunction with a linear linker for the selective
synthesis of a rectangle (Scheme 9.2).
Scheme 9.2
Selective formation of a molecular rectangle via a [2 + 2] self-
assembly using a molecular “clip” acceptor in combination
with a linear donor.
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