Resolving ambiguity: an integrated approach to bending geometry identification in flexible organic crystals

The unambiguous identification of all crystallographic faces and directions, including those associated with plastic bending, is a prerequisite for establishing reliable structure–property relationships in flexible organic crystals. Conventional face indexing via single-crystal X-ray diffraction (SCXRD) is often compromised by the morphological imperfections typical for these materials and the technical limitations of diffractometer on-axis optical microscopes. This work introduces and validates an integrated analytical protocol that synergistically combines computational morphology prediction, precise interfacial angle measurement via scanning electron and optical microscopy, and directed SCXRD indexing enhanced by internal (crystal bend) and external (mount) geometric standards. Applied to the plastically bendable crystals of α-pyrazinamide, 1,3,5-trichlorobenzene and L-leucinium hydrogen maleate, this multi-technique framework conclusively resolved their bending geometries, identifying the primary bending faces and directions as (002)/[100], {011}/[100] and (20 1 )/[010], respectively. Crucially, while the bending plane can be identified via SCXRD standards alone, the full protocol is mandatory for determining all morphological faces, providing the complete dataset essential for computational analysis and predictive model building. This workflow overcomes the ambiguities inherent to any single method and provides a robust, generalizable framework for the reliable morphology characterization of mechanically flexible molecular crystals.