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Rapid Discrimination of Crystal Handedness by X-ray Natural Circular Dichroism (XNCD) Mapping |
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| Authors: | Dr Miguel Cortijo Dr Ángela Valentín-Pérez Dr Andrei Rogalev Dr Fabrice Wilhelm Dr Philippe Sainctavit Dr Patrick Rosa Dr Elizabeth A Hillard |
| Institution: | 1. CNRS, ICMCB, UMR 5026, 33600 Pessac, France
Université de Bordeaux, ICMCB, UMR 5026, 33600 Pessac, France CNRS, CRPP, UMR 5031, 33600 Pessac, France Université de Bordeaux, CRPP, UMR 5031, 33600 Pessac, France;2. CNRS, ICMCB, UMR 5026, 33600 Pessac, France Université de Bordeaux, ICMCB, UMR 5026, 33600 Pessac, France CNRS, CRPP, UMR 5031, 33600 Pessac, France Université de Bordeaux, CRPP, UMR 5031, 33600 Pessac, France Deceased.;3. European Synchrotron Radiation Facility (ESRF), 38043 Grenoble, France;4. IMPMC, CNRS, Sorbonne Université, Muséum National d'Histoire Naturelle, UMR7590, 4 place Jussieu, 75252 Paris Cedex 05, France;5. CNRS, ICMCB, UMR 5026, 33600 Pessac, France;6. CNRS, CRPP, UMR 5031, 33600 Pessac, France |
| Abstract: | 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 %). |
| Keywords: | chirality conglomerate crystallization coordination chemistry X-ray absorption X-ray optical activity |