Quantifying d-d and Metal-Ligand Interactions across Distant Metal Sites as a Function of Ligand Architecture and...

The control of electron transfer pathways in transition metal complexes is crucial for developing next-generation molecular devices and photocatalysts. Herein, the electronic structure and charge delocalization mechanisms in trinuclear trans-[(NC)₅Fe ${}^{\text{III}}$ (μ-CN)Ru ${}^{\text{II}}$ (L)₄(μ-NC)Fe ${}^{\text{III}}$ (CN)₅]^4- complexes (L = pyridine, 4-methoxypyridine) using complementary X-ray spectroscopic techniques at the Ru L₃-edge are investigated. By combining 2p3d and 2p4d resonant inelastic X-ray scattering spectroscopy with quantum mechanics/molecular mechanics simulations and time-dependent density functional theory-based X-ray calculations, the modulation of the X-ray spectral features as a function of the ligand architecture and solvent environment are probed. Analysis of the experimental data reveals that ligand field interactions systematically tune charge distribution across the metal-cyanide backbone. A novel pre-edge feature arising from Fe-Ru d-d coupling that directly correlates with the near IR metal-to-metal charge transfer transition energies is identified. These findings aid in establishing the design principles for developing multimetallic complexes with tailored electronic coupling.