Structural determination of coordination compounds is essential across the chemical sciences. In particular, there is a need for techniques that can be applied to compounds that are composed primarily of heteroatoms, can only be synthesized in small quantities, and do not readily crystallize. Real-space, atomic-resolution electron microscopy (EM) imaging is an approach where the structure can be directly elucidated from an image, sidestepping the potential for misassignments that can occur with less direct methods. Furthermore, real-space imaging offers a powerful complement to diffraction methods, such as x-ray crystallography and micro-electron diffraction, as it does not require input models, avoids the challenges associated with inverting real-space structures from diffraction data, and is intrinsically well-suited to analyzing extremely small volumes of materials, including nanocrystalline or even amorphous samples. This talk will demonstrate atomic-resolution EM imaging of metalated porphyrin and phthalocyanine derivatives. We apply aberration-corrected scanning transmission EM to monolayer crystals supported by atomically thin graphene substrates, which allows us to detect and locate single complexes. We then adapt data processing methods from 2D crystallography and cryo-EM to combine frames acquired from 10<sup>2</sup>-10<sup>5</sup> individual complexes into a single averaged image. These methods produce images with elemental sensitivity and up to 1.3 Å resolution, sufficient to distinguish the individual atoms, as is demonstrated in Figure 1. These results indicate a new route for atomic-scale electron microscopy imaging to solve the structures of coordination compounds.

Atomic-resolution imaging of coordination compounds on graphene

ACS Spring Meeting 2021

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