Vibrational Circular Dichroism Spectra of Atomically‐Precise Metal Clusters: Unveiling Conformational Structures and Mechanism of VCD Enhancement via Full Models

While the inherent imprecision of nanoparticles has hindered a thorough comprehension of chirality transfer and enhancement events at the nanoscale, recent advances in ultrastable, chiral metal clusters offer a unique opportunity to tackle this challenge with atomic precision. Four atomically-precise metal clusters with octahedral metal cores protected by monolayer organic ligands, namely Ag₆PL₆/PD₆, and Cu₆PL₆/PD₆ (PL₆/PD₆ = (S)-/(R)-4-phenylthiazolidine-2-thione) are investigated using vibrational circular dichroism (VCD) in conjunction with theoretical modeling and electronic CD. Extensive and systematic conformational searches are carried out for the ligand and metal clusters. The IR and VCD spectra of the most stable conformers are simulated using full models, demonstrating excellent agreements with experiment and uncovering the preferred ligand conformational arrangements. A modified modes approach is developed to unveil the roles of individual ligands, their collective arrangements and numbers, and the metal core asymmetry in the drastic VCD enhancement. While commonly used truncated models with fewer metal atoms and/or ligands exhibit their critical deficiencies, the full models provide a solid foundation for accurately predicting the chiral properties of nanosized materials.