Probing Molecular Chirality from Vibrational to X-ray Energies in Cr(III) and Co(III) Complexes
Year: 2026
Type: preprint
Abstract: The expression of molecular chirality across widely separated energy regimes was investigated in enantiomeric Cr(III) and Co(III) tris(trans-1,2-cyclohexanediamine) complexes using vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and X-ray natural circular dichroism (XNCD), supported by single-crystal X-ray diffraction and density functional theory (DFT). Crystallographic analysis establishes the Λ-δδδ/lel3 and Δ-λλλ/lel3 configurations in the solid state, while the ECD spectra and comparison of experimental and DFT-calculated VCD spectra support retention of the lel3 stereochemical arrangement in solution. At the Co K-edge, pronounced opposite-sign XNCD responses are observed in the pre-edge region, with an amplitude approximately 1.5 times that previously reported for the Co(III)–ethylenediamine system measured in axial geometry, corresponding to an estimated threefold enhancement under equivalent axial conditions. At the Cr K-edge, a clear, reproducible and well-resolved enantiomer-dependent XNCD response, featuring several distinct dichroic contributions, is observed, despite its lower amplitude relative to the Co analogue. To the best of our knowledge, this constitutes the first clear experimental observation of XNCD at the Cr K-edge. The distinct XNCD responses of these structurally related Cr(III) and Co(III) complexes demonstrate the sensitivity of K-edge XNCD to differences in the local chiral electronic environment of transition-metal centers.
Source: ChemRxiv
Language: English
Subfield: Spectroscopy
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7222660937