Versatile solid forms of boscalid: insight into the crystal structures and phase transformations
Boscalid, a blockbuster in the field of fungicides, is mainly used for controlling gray mold, powdery mildew, sclerotia. The aim of this study was to investigate the solid forms of boscalid systematically. The powder production of two anhydrous polymorphs (form I, form II) and monohydrate (H1) have been reported in the references, while three novel solvates, i.e. S1 (1,4-dioxane solvate), S2 (N-methyl pyrrolidone solvate) and S3 (dimethyl sulfoxide solvate) have been obtained for the fist time. The physicochemical properties of these six solid forms were fully characterized including power X-ray diffraction, scanning electron microscope, Fourier transform-infrared spectroscopy, solid-state NMR, thermal analysis. Crystal structures of all the six solid forms were determined from single crystal data. The molecule conformations and packing arrangements in the crystal structures were analyzed and compared. Hirshfeld surface analysis was applied to reveal the intermolecular interactions. The packing coefficients of crystal forms have been calculated to explain the formation of solvates. Finally, the desolvation process of solvates and the transformation relationship between different phases were explored. Meanwhile, the desolvation of solvate S2 leads to form II suitable for practical applications.