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Natural Circular Dichroism beyond Chirality
Elen Duverger-Nédellec1, Alessandro De Frenza2, Patrick Rosa1
1Univ. Bordeaux, CNRS, Bordeaux INP, ICMCB, UMR 5026, F-33600 Pessac, France.
Journal of the American Chemical Society
|June 23, 2025
Summary
Researchers used X-rays to observe natural circular dichroism in achiral crystals, overcoming UV-vis measurement limitations. This finding confirms symmetry predictions and reveals insights into crystal structure determination.
Area of Science:
- Solid-state physics
- Crystallography
- Spectroscopy
Background:
- Natural optical activity in crystals is predicted by symmetry but difficult to measure in UV-vis ranges due to birefringence.
- Achiral point groups theoretically allow for optical activity, but experimental verification is challenging.
Purpose of the Study:
- To experimentally demonstrate natural circular dichroism in specific achiral crystal systems.
- To investigate the influence of crystal symmetry on optical activity using X-ray spectroscopy.
- To explore the relationship between crystal point groups, space groups, and observed optical phenomena.
Main Methods:
- Utilized X-ray spectroscopy to probe copper and iron coordination salts.
- Focused measurements at the K-edges of copper and iron.
- Analyzed experimental data against symmetry predictions for achiral point groups (4̅2m and 4̅).
Main Results:
- Successfully observed natural circular dichroism in copper and iron coordination salts crystallizing in achiral point groups.
- Experimental angular dependence of circular dichroism matched theoretical predictions based on point group symmetry.
- An angular phase shift was observed for the 4̅ point group, attributed to space group translation operations.
Conclusions:
- X-ray spectroscopy provides a viable method for measuring natural circular dichroism in achiral crystals, overcoming UV-vis limitations.
- The study validates symmetry-based predictions for optical activity in specific achiral crystal structures.
- Space group symmetry, specifically translation operations, plays a crucial role in defining crystalline axes, impacting observed optical properties.
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