Theoretical Assessment of Magneto-Chiral Dichroism in a Chiral Ytterbium(III) Complex.

The first ab initio simulation of Magneto-Chiral Dichroism (MChD) for a lanthanide-based complex is reported. The previously experimentally studied [Yb(hfac)3(P-H6bpy)] complex is investigated with multireference wavefunction-based methods using complete active space self-consistent field (CASSCF) calculations, further refined by second-order perturbation theory (CASPT2) and state-interaction spin-orbit approach (RASSI-SO), in combination with the microscopic MChD theory developed by Barron and Vrbancich (BV). The simulations enable a detailed analysis of the 2F5/2 ← 2F7/2 electronic transitions. At 4 K, the MChD response is found to be dominated by the MChD Cterm contribution, arising from electric dipole-magnetic dipole interactions and population differences within the ground state, split by the magnetic field. Overall, the simulated spectrum shows good agreement with experiment in terms of both relative transition energies and band-sign assignments. Zeeman splitting was explicitly evaluated and found to be negligible under the experimental conditions, indicating that vibronic coupling is the most likely origin of the remaining discrepancies. By providing a quantitative and physically grounded description of the MChD spectrum of a lanthanide complex, this work goes beyond the current state of the art in theoretical simulations of MChD and fills a crucial gap, at a time when the growing body of experimental data on lanthanide complexes calls for direct theory-experiment comparisons to enable deeper interpretation.