Engineering short, strong, charge-assisted hydrogen bonds in benzoic acid dimers through co-crystallisation with proton sponge

A series of molecular complexes of the proton sponge 1,8-bis(dimethylamino)naphthalene (DMAN) with mono-substituted halobenzoic acids are reported, illustrating the designed exploitation of the characteristics of the proton sponge to induce short, charge-assisted hydrogen bonds in a predictable and reproducible manner. In every case, a DMAN molecule extracts a proton from the carboxylic acid group of the benzoic acid, as a result of which a recurrent supramolecular unit between a neutral and a deprotonated benzoic acid molecule is formed featuring an extremely short, strong O-H•••O hydrogen bond, within a predominant crystallisation ratio of 1:2 (DMAN:benzoic acid).