Synthon Modularity in 4‑Hydroxybenzamide–Dicarboxylic Acid Cocrystals

A family of 4-hydroxybenzamide–dicarboxylic acid
cocrystals has been designed and subsequently isolated and characterized.
The design strategy follows from an understanding of synthon modularity
in crystal structures of monocomponent crystals such as γ-quinol,
4,4′-biphenol and 4-hydroxybenzoic acid. These monocomponent
structures contain infinite O–H···O–H···O–H···
cooperative synthons linked with molecular connectors such as phenyl
and biphenyl, and supramolecular connectors such as the acid dimer
in 4-hydroxybenzoic acid. The cocrystal design was influenced by the
anticipation that dicarboxylic acids can form a supramolecular connector
mediated by acid–amide synthons with 4-hydroxybenzamide, which
can then form the phenol O–H···O–H···O–H···
infinite synthon. Effectively, the acid–amide and phenol synthons
are insulated. The short axis of such a structure will be around 5.12
Å and this is borne out in 2:1 cocrystals of 4-hydroxybenzamide
with oxalic, succinic, fumaric, glutaric (two forms) and pimelic acids.
Hydrated variations of this structure type are seen in the cocrystals
obtained with adipic and sebacic acids.