Co-crystallisation of benzoic acid with sodium benzoate: the significance of stoichiometry†
Currently the synthesis of co-crystals is receiving considerable attention. We studied co-crystallisation of benzoic acid with sodium benzoate in different ratios and with different crystallisation techniques. A crystalline co-crystal, composed of two equivalents of benzoic acid and one equivalent of sodium benzoate (2 HBz·1 NaBz) could be identified and structurally characterised. By concomitant coordination of benzoate and benzoic acid the coordination needs of the cation could be satisfied. However, even with a 2 : 1 ratio, an octahedral environment could only be realised by sharing an edge in a dimer. The dimers are connected to one-dimensional tapes which in turn are packed in a distorted hexagonal arrangement. Only with a ratio of two neutral benzoic acid ligands and one benzoate can the coordination requirements of the sodium cation and charge neutrality be assured at the same time.