Structure of sodiumpara-hydroxybenzoate, NaO2C–C6H4OH by powder diffraction: application of a phenomenological model of anisotropic peak width

Abstract

Theab initiostructure solution of sodiumpara-hydroxybenzoate from high-resolution X-ray powder diffraction data is reported. The compound is of interest with respect to understanding the mechanism of Kolbe–Schmitt type reactions. It crystallizes in space groupP21,Z= 2, with unit-cell parametersa= 16.0608 (3),b=  5.38291 (9),c=  3.63834 (6) Å, β =  92.8692 (5)° andV=  314.153 Å3. The compound consists of layers of distorted NaO6prisms perpendicular to theaaxis and phenol rings perpendicular to these layers pointing up and down. The molecular structure is held together by van der Waals forces between the phenyl groups of different layers and additional hydrogen-bridge bonding between the phenolate oxygen atoms. The sample showed powder peak widths which are not a smooth function of diffraction angle; a recently implemented phenomenological model was able to describe this effect sufficiently well to obtain excellent Rietveld fits to the data. The accuracy of modeling the data makes this one of the rare cases where the position of a hydrogen atom could be unambiguously determined by powder techniques.