The Crystal and Molecular Structure of p -Hydroxybenzoic Acid Monohydrate

Abstract

The crystal and molecular structure of p-hydroxybenzoic acid monohydrate has been determined by a single crystal X-ray analysis. The crystals are monoclinic, space group P21⁄a, Z=4, with a=17.79, b=6.39, c=6.79 Å, and β=105.6°. The structure was solved by the Patterson and Fourier methods, and refined by the block-diagonal least-squares method to a final R value of 0.086 for 806 non-zero reflections. Pairs of acid molecules form dimers by the hydrogen bonds between carboxyl groups (2.678 Å). The dimers are held together by the hydrogen bonds between phenolic hydroxyl groups and water molecules (2.595 and 2.823 Å); these hydrogen bonds extend around two-fold screw axes to make up layers of the dimers parallel to the (401). The layers are linked by the additional hydrogen bonds between carbonyl oxygens and water molecules (2.823 Å).