Characterization of pseudopolymorphs of a hydroxybenzoic acid derivative

Abstract

Hydroxybenzoic acid is used in many applications, including medicine and polymer synthesis. The synthesis, self-assembly, and characterization of three pseudopolymorphs of a derivative of a widely used 4-hydroxybenzoic acid (1) are described in detail. In this investigation, we have incorporated hydrophobic (biphenyl groups) and hydrophilic (-OH and -CO2H) groups on an aromatic ring to influence the self-assembly in the solid lattice. Compound 1 crystallizes into three crystalline forms: (i) monoclinic from a solution of DMSO (1A), (ii) triclinic from a 1:1 solution of DMSO/hot ethyl acetate (1B), and (iii) triclinic from pyridine solution (1C). The formation of these pseudopolymorphs and the structural similarities in their packing motifs can be rationalized through a few multipoint solute-solvent interactions. In all three structures, the crystallographic aspects pertaining to the influence of solvent molecules towards the formation of hydrogen bonded network structures are described. In addition to the strong hydrogen bonds, intermolecular C-H⋯O, C-H⋯π, and π⋯π interactions were found to stabilize the crystal structures.