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.