Application of Multiple Small-wedge Synchrotron Crystallography for Post-reaction Structural Characterization of a Stimuli-responsive Small-molecule Crystal

Abstract Organic crystals have been known to exhibit unique solid state reactivities depending on both molecular structures and crystal packings. Crystal structure determination before and after an in-crystallo reaction is one of the most powerful approaches for elucidating the mechanism. However, crystals often undergo degradation of their long-range order upon the reaction, preventing single-crystal X-ray structural analysis of the reacted crystals. Here we report application of multiple small-wedge synchrotron crystallography (SWSX) at BL41XU, SPring-8 to crystal structure determination of topochemically polymerized 7,7,8,8-tetrakis(methoxycarbonyl)-p-quinodimethane. The polymer crystal structure was determined using both conventional data collection by an in-house diffractometer and SWSX, indicating single-crystal-to-single-crystal topochemical polymerization. SWSX resulted in much lower mosaicity while the conventional approach suffered from elongated diffraction spots. This was attributed to the fact that the diffraction by microbeam SWSX arises from crystals with fewer mosaic blocks. The findings of this study highlight the potential applicability of SWSX to various small-molecule crystals in chemical crystallography, e.g. those that transform into less-ordered states with high mosaicity, defects and/or polycrystals, by stimuli-induced solid-state reactions.