Supramolecular synthons in crystals are structural units formed
with intermolecular interactions. The
assembly of an organic crystal is not just a geometrical interlinking
with synthons but is often the consequence of
compromise or mutual interference between adjacent synthons.
Accordingly, synthon interference can be a major
problem in systematic crystal engineering especially if it results in a
lack of correspondence between molecular and
crystal structures. Conversely, synthon robustness or the capacity
to withstand interference is an essential attribute
in crystal structure design. These ideas are illustrated with
reference to the structural chemistry of a series of 1,4-disubstituted 2,3-dicyano-5,6-dichlorobenzenes and related compounds.
The supramolecular synthons in this structural
family are constructed with polarization-induced C⋮N···Cl
interactions. Synthon interference is analyzed in
terms
of the trade-off between these interactions on the one hand and
hydrophobic and CH···N interactions on the other.
Topological relationships between these C⋮N···Cl
synthons and others containing stronger hydrogen bond
interactions
lead to similarities in the networks formed in the crystal structures
of compounds, which at the molecular level, are
widely disparate.
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