Dr. James Hohman

Dr. James Nathan Hohman

University of Connecticut
Department of Chemistry

Friday, October 28, 2022
12:00 Noon 
Room 120 – Meyerhoff Chemistry Department
HOST:  Dr. Minji Kyoung

“Shining Light on Crystallographic Dark Matter”

The ready availability of single crystal X-ray diffraction has led to a wealth of new materials characterized each year. However, known material structures are biased towards those that are easily crystallized.  Hybrid materials in particular trend towards crystals too small or otherwise pathological to be used for traditional characterization techniques. These “dark” materials that are too difficult to characterize make up a large portion of hypothetical hybrid materials. Here, we used a new technique of serial femtosecond chemical crystallography (SFCX) that uses the high brightness of an X-ray free-electron laser to acquire diffraction from crystals in the 1-5 micron range. Graph theory is used to index those snapshots, enabling determination of crystal structure. We used this technique to explore the ligand environment with variables of steric hinderance, functional group, and intermolecular forces, each addressed by selecting different ligand shapes and configurations. We find dramatic differences in the connectivity, topology, and dimensionality of the resulting silver organothiolates. Of note is the nature of the Ag-Ag interactions, which appear to be an important component of the fine structure of the silver systems. The Ag-Ag networks are found to rearrange as a function of the supramolecular ordering of each example system.

Nathan Hohman
University of Connecticut
Institute of Materials Science
Assistant Professor of Chemistry


 Serial femtosecond crystallography utilizes a bright x-ray pulse and a jet of microcrystals to yield partial diffraction patterns. (middle) Examples of three microcrystal suspensions: thiorene [AgSPh], mithrene [AgSePh], tethrene [AgTePh]. (bottom) The mithrene and tethrene are structural homologs with 2D Ag-Ag networks, and the thiorene exhibits a new 1D Ag-Ag network and loses the optical properties of the other members.