Rapid discrimination of crystal handedness by XNCD mapping

Miguel Cortijo (1, 2) , Ángela Valentín-Pérez (1, 2) , Andrei Rogalev (3) , Fabrice Wilhelm (3) , Philippe Sainctavit (4) , Patrick Rosa (1) , Elizabeth Anne Hillard (1, 2)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
2 CRPP - Centre de Recherche Paul Pascal
3 ESRF - European Synchrotron Radiation Facility
4 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie

An original method for determining the handedness of individual non‐centrosymmetric crystals in a mixture using a tightly‐focused, circularly polarized X‐ray beam is presented. The X‐ray natural circular dichroism (XNCD) spectra recorded at the metal K‐edge on selected crystals of [Δ‐M(en)3](NO3)2 and [Λ‐M(en)3](NO3)2 (M=CoII, NiII) show extrema at the metal pre‐edge (7712 eV for Co, 8335 eV for Ni). A mapping of a collection of some 220 crystals was performed at the respective energies by using left and right circular polarizations. The difference in absorption for the two polarizations, being either negative or positive, directly yielded the handedness of the crystal volume probed by the beam. By using this technique, it was found that the addition of l‐ascorbic acid during the synthesis of [Co(en)3](NO3)2 resulted in an enantiomeric enrichment of the Λ‐isomer of 67±13 %, whereas the Ni analogue was similarly, but conversely, enriched in the Δ‐isomer (65±22 %).

Mots clés: Chirality; Conglomerate crystallization; Coordination chemistry; X-ray absorption; X-ray optical activity

Domaines: Chimie de coordination; Cristallographie

Miguel Cortijo, Ángela Valentín-Pérez, Andrei Rogalev, Fabrice Wilhelm, Philippe Sainctavit, et al.. Rapid discrimination of crystal handedness by XNCD mapping. Chemistry - A European Journal, 2020, 26 (59), pp.13363-13366. ⟨10.1002/chem.202001783⟩. ⟨hal-02945207⟩