We have two identical hands – almost. They are mirror images, or chiral. Jacob Wright from Empa in Switzerland demonstrated at EUROPACAT2025 that metals can also have such a structure.
Figure 1: Chirality represented by two enantiomers of a chiral molecule, which are similar to each other as the right and left hand. (Image source: Wikipedia)
The surface structure of such crystals can also exhibit chirality. The catalyst is pleased with such a formative substrate, because an equally chiral adsorbate will take over the configuration. And that is the dream of fine chemical catalysis: to produce enantiomerically pure substances, to select cis-trans configuration, to produce R- or S-pure substances. An example of a prochiral, larger organic molecule on a chiral metal interface can be seen in the second image.
Figure 2: Non-contact AFM image of the R and S enantiomeric complex of 9-ethynylphenanthrene on a chiral PdGa:B(111) surface.
Specific alloy mixtures, namely intermetallic compounds of the crystalline space group 198 such as PdGa, PtAl, etc., exhibit the same type of mirror symmetry breaking as seen in our hands. These metals display chirality, and research is currently underway to use them as chirally selective catalysts in surface reactions. All volume-terminated surfaces are chiral and, despite similar electronic structures, exhibit different geometric arrangements that can be exploited for specific reactions. (Courtesy of Empa Switzerland – nanotech@surfaces – Chiral Surfaces; contact: jacob.wright@empa.ch.)
Further reading:
– Samuel Stolz, PhD thesis “Exploiting the chirality of intermetallic PdGa”, EPFL (2020); https://infoscience.epfl.ch/entities/publication/6f335d94-f9af-45d1-a649-067b23662143
– S. Stolz, et al. “Asymmetric azide-alkyne Huisgen cycloaddition on chiral metal surfaces”, Communications Chemistry 4, 51 (2021)
