XFEL Microcrystallography of Self-Assembling Silver n-Alkanethiolates

New synthetic hybrid materials andtheir increasing complexityhave placed growing demands on crystal growth for single-crystal X-raydiffraction analysis. Unfortunately, not all chemical systems areconducive to the isolation of single crystals for traditional characterization.Here, small-molecule serial femtosecond crystallography (smSFX) atatomic resolution (0.833 & ANGS;) is employed to characterize microcrystallinesilver n-alkanethiolates with various alkyl chainlengths at X-ray free electron laser facilities, resolving long-standingcontroversies regarding the atomic connectivity and odd-eveneffects of layer stacking. smSFX provides high-quality crystal structuresdirectly from the powder of the true unknowns, a capability that isparticularly useful for systems having notoriously small or defectivecrystals. We present crystal structures of silver n-butanethiolate (C4), silver n-hexanethiolate (C6),and silver n-nonanethiolate (C9). We show that anodd-even effect originates from the orientation of the terminalmethyl group and its role in packing efficiency. We also propose asecondary odd-even effect involving multiple mosaic blocksin the crystals containing even-numbered chains, identified by selected-areaelectron diffraction measurements. We conclude with a discussion ofthe merits of the synthetic preparation for the preparation of microdiffractionspecimens and compare the long-range order in these crystals to thatof self-assembled monolayers.

Automated summary

In this study, smSFX method was used to successfully characterize the structure of silver n-alkanethiolates at atomic resolution, resolving long-standing controversies regarding atomic connectivity and odd-even effects of layer stacking. This method allows for high-quality crystal structures directly from the powder of unknown samples, which is particularly useful for systems with small or defective crystals.