A structural study of polymorphism in phenyl salicylate: determination of the crystal structure of a meta-stable phase from X-ray powder diffraction data using a direct space systematic search method

摘要

In this paper we report the crystal structure solution of a meta-stable phase of phenyl salicylate (salol). This modification, which is obtained from a super-cooled melt, has been observed before, but the structure has not been previously determined. Structure solution was achieved by a procedure combining a computer based systematic search method with a subsequent Rietveld refinement of experimental X-ray powder diffraction data. A clustering procedure to group similar trial structures based upon energy minimisations is discussed. The best trial structure identified by the combination of a systematic search and clustering was refined using the Rietveld method and a final structure with a weighted pattern index R_(wp) of 0.0513 (excluding background) was obtained. The meta-stable phase of salol crystallises with a monoclinic unit cell with cell parameters a = 17.4047(8) A, b = 5.9800(5) A, c = 10.6882(7) A, and β = 108.988(5)°. The space group is P2_1 with four molecules in the unit cell. A structural comparison of the stable and meta-stable modifications is given.