198 Topics in Current Chemistry Editorial Board: A. de Meijere KN ...

Supramolecular Synthons and Pattern Recognition 61
1 2 3
5
8
6 7
9 10
11 12 13
Scheme 1. Some supramolecular synthons selected from the recent literature
of non-bonded interactions between molecules. Networks constituted with
node and node connections may be thus defined. It is profitable to describe
targets in crystal engineering in terms of such networks [12]. Retrosynthetic
analysis may be performed accordingly on the network structure to yield the
node structure (molecules) and the node connectivity (supramolecular synthons).
The advantages of such an approach in crystal engineering are that: (1)
supermolecule molecule connections are easily established; (2) comparisons
between seemingly different crystal structures are facilitated; (3) the interference
between supramolecular synthons can be strategically minimised; and (4) more
than one combination of molecular and supramolecular synthons are seen to
lead to similar crystal structures.
To illustrate this last point, the structures of tetrakis(4-bromophenyl)methane
(15) and the 1:1 molecular complex 20 of CBr 4 and tetraphenylmethane 14
(Scheme 2) are pertinent [13]. In the crystal structure of 15, four Br atoms are
arranged in a tetrahedral fashion and form the Br 4-synthon 18 (Br◊◊◊Br 3.91 Å).
If the empty centroid in synthon 18 is considered to be a phantom “carbon”
4