Polymorphism of 3-hydroxy-2-naphthoic acid: crystal structures, Hirshfeld surface analysis and properties

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Polymorphs play an important role in mediating the physical properties of compounds. Therefore, a set of polymorphs based on 3‑hydroxy-2-naphthoic acid (HA), namely, α-HA (1), β-HA (2) and γ-HA·DMF (3) (DMF = N,N-dimethylformamide), were obtained by slow evaporation method, which were the solution of HA in ethanol, acetone and DMF, respectively. These crystal morphologies of HA have been characterized by single–crystal X–ray diffraction, IR and UV–Vis, and powder X-ray diffraction. In these polymorphism, classical hydrogen bonds of O–H∙∙∙O can be obviously observed, through which a supramolecular architecture will be generated. Apart from the classical hydrogen bonds, the hydrogen bonds of C–H⋯O can be only found in form γ-HA. The luminescent maximal are 497, 504 and 510 nm for α-HA,β-HA andγ-HA·DMF, respectively. The order of the maximal peaks is listed as the following: 3 > 2 > 1. Single-crystal X-ray diffraction analysis results reveal that the order of the distances between the aromatic rings is 3 > 2 > 1. The Hirshfeld analysis further confirm that there exists the largest contribution of the H∙∙∙H and H∙∙∙O close contacts in compound 3, which is in a good agreement with of the luminescent maxima in compound 3.