Circular Dichroism at the Edge:  Large X-ray Natural CD in the 1s → 3d Pre-Edge Feature of 2[Co(en)₃Cl₃]·NaCl·6H₂O

Hard X-ray magnetochiral dichroism in a paramagnetic molecular 4f complex

“…On the contrary, ample experimental evidence demonstrates signicant electric quadrupole contributions to hard X-ray absorption spectra. 35 Thus, optical activity effects in the hard X-ray range arise from interference of electric dipole and electric quadrupole transitions as it has been experimentally demonstrated [36][37][38] and theoretically conrmed. 39 These interference contributions average to zero in randomly oriented samples (polycrystalline powders or liquids) and can only be detected on orientation ordered systems, e.g.…”

On circular dichroism and the separation between chromophore and chiral center: The near carbon K‐edge X‐ray absorption and circular dichroism spectra of noradrenaline and L‐DOPA

“…The much less exploited counterpart of ECD in the X‐ray region is known as X‐ray natural circular dichroism (XNCD),6 and one here is concerned with core electronic excitations which, for biological systems, means that the probed excited states are often those at the near K‐edges of carbon, nitrogen, and oxygen. In oriented samples, the electric‐dipole–electric‐quadrupole interaction can dominate the XNCD response, but in randomly oriented samples, when this contribution vanishes, the circular dichroism is governed by the electric‐dipole–magnetic‐dipole interaction 7–11. We will focus at this latter interaction and view it in perspective of the aforementioned discussion about the dependence of signal response on spatial separation of chromophore and chiral center.…”

X-ray detected optical activity

“…As an illustration, we have reproduced in Fig. 3 the cobalt K-edge XAS and XNCD spectra recorded with two enantiomeric single crystals of a chiral propeller-like organometallic complex 2[Co(en) 3 Cl 3 ]· NaCl· 6H 2 O, in which the ligand field has the enantiomorphous D 3 point group symmetry [8]. Note that the organometallic complex [Co(en) 3 ] 3+ ion has long served as a paradigm in the structural and theoretical chemistry of chiral transition metal compounds.…”

“…The existence of optical activity in the X-ray range has remained a fully open question for nearly one century until X-ray Natural Circular Dichroism (XNCD) was unambiguously detected at the ESRF in quite a few non-centrosymmetric crystals [5][6][7][8]. What made such experiments feasible was the recent availability of intense beams of circularly polarized X-rays at third-generation synchrotron radiation sources.…”