The trimorphism of 3-hydroxybenzoic acid: an experimental and computational study

Following the computational prediction that 3-hydroxybenzoic acid (3HBA) could exist in more than the two literature polymorphs, an experimental investigation targeting computationally generated structures was performed. The third polymorph III, solved from powder X-ray diffraction data, and the literature form II share a common hydrogen-bonded ladder motif in contrast to the carboxylic acid dimer based form I. The two metastable polymorphs (II and III) are storage stable if phase pure and monotropically related to form I. Calorimetric measurements and (lattice) energy minimisations revealed that the three polymorphs are close in energy.