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Published February 2021 | Supplemental Material + Submitted
Journal Article Open

Elucidation of Diverse Solid‐State Packing in a Family of Electron‐Deficient Expanded Helicenes via Microcrystal Electron Diffraction (MicroED)


Solid-state packing plays a defining role in the properties of a molecular organic material, but it is difficult to elucidate in the absence of single crystals that are suitable for X-ray diffraction. Herein, we demonstrate the coupling of divergent synthesis with microcrystal electron diffraction (MicroED) for rapid assessment of solid-state packing motifs, using a class of chiral nanocarbons—expanded helicenes—as a proof of concept. Two highly selective oxidative dearomatizations of a readily accessible helicene provided a divergent route to four electron-deficient analogues containing quinone or quinoxaline units. Crystallization efforts consistently yielded microcrystals that were unsuitable for single-crystal X-ray diffraction, but ideal for MicroED. This technique facilitated the elucidation of solid-state structures of all five compounds with <1.1 Å resolution. The otherwise-inaccessible data revealed a range of notable packing behaviors, including four different space groups, homochirality in a crystal for a helicene with an extremely low enantiomerization barrier, and nanometer scale cavities.

Additional Information

© 2020 Wiley-VCH. Issue Online: 25 January 2021. Version of Record online: 27 November 2020. Accepted manuscript online: 08 October 2020. Manuscript received: 07 September 2020. A large portion of this work was funded by the National Science Foundation under Grant No. CHE-1708210. C.G.J. acknowledges the National Science Foundation Graduate Research Fellowship Program (DGE-1650604), the Christopher S. Foote Fellowship, and the Pat Tillman Foundation for funding. J.O. acknowledges the National Science Foundation Graduate Research Fellowship Program (DGE-1650604) for funding. H.M.N. acknowledges the Packard Foundation and Bristol Myers Squibb for generous funding. A.E.S. thanks Robert H. Grubbs for use of facilities and helpful discussions. The authors thank Jose Rodriguez, Duilio Cascio, Michael R. Sawaya and Michael J. Collazo (UCLA) for assistance with MicroED data collection and processing, and Vincent LaVallo, Yan Xu and William Wolf for helpful general discussions. The computational work was performed at the UC Berkeley Molecular Graphics and Computation Facility (MGCF), which is supported by the National Institute of Health (Grant No. NIH S10OD023532), and the authors thank Dave Small for his assistance with these calculations. This work incorporates data collected at the Northeastern Collaborative Access Team (NE-CAT) beamlines at Argonne National Laboratory. NE-CAT is funded by the NIH-NIGMS (Grant No. P30 GM124165). The Pilatus 6M detector on the 24-ID-C beamline is funded by NIH-ORIP HEI (Grant No. S10 RR029205). This work also used resources at the Advanced Photon Source, a U.S. Department of Energy Office of Science User Facility operated by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. The UCLA-DOE Institute's X-ray Crystallography Core Facility is supported by the U.S. Department of Energy (Grant No. DE-FC02-02ER63421). The authors declare no conflict of interest.

Attached Files

Submitted - micro-ed-elucidation-of-diverse-solid-state-packing-in-a-family-of-electron-deficient-expanded-helicenes.pdf

Supplemental Material - anie202012213-sup-0001-misc_information.pdf



Additional details

August 22, 2023
October 23, 2023