Just Accepted Articles have been posted online after technical editing and typesetting for immediate view. The final edited version with page numbers will appear in the Current Issue soon.
Heterometallic 3d-4f clusters represent a promising class of multifunctional molecular materials, driven by the synergistic interactions between d- and f-electrons. Incorporating chirality into these systems further expands their potential applications, particularly in chiroptical and magneto-optical technologies. Herein, we report the successful synthesis of chiral [Ln3Co5] (Ln = Er and Y) clusters using binaphthol-based ligands. Single-crystal X-ray diffraction reveals the coexistence of two distinct Co2+ coordination geometries: six-coordinate octahedral and five-coordinate trigonal bipyramidal. Spectroscopic analyses demonstrate geometry-dependent chiroptical behavior: pentacoordinate Co2+ ions predominantly contribute to the circular dichroism (CD) features, while both geometries exhibit distinguishable signals in the magnetic circular dichroism (MCD) spectra. Notably, a pronounced magnetic dipole transition (4I15/2 → 4I13/2) from Er3+ centers is observed in the near-infrared MCD region, displaying a high g-factor of 0.0078 T-1. This work highlights the configuration- and ligand field-dependent chiroptical responses in 3d-4f systems, providing new insights for the rational design of advanced magneto-optical devices.