Quantifying d‐d and Metal–Ligand Interactions across Distant Metal Sites as a Function of Ligand Architecture and Solvent

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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msup><mml:mrow></mml:mrow> <mml:mrow><mml:mtext>III</mml:mtext></mml:mrow> </mml:msup> </mml:mrow> <mml:annotation>$^{\text{III}}$</mml:annotation></mml:semantics> </mml:math> (μ-CN)Ru <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msup><mml:mrow></mml:mrow> <mml:mrow><mml:mtext>II</mml:mtext></mml:mrow> </mml:msup> </mml:mrow> <mml:annotation>$^{\text{II}}$</mml:annotation></mml:semantics> </mml:math> (L)₄(μ-NC)Fe <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msup><mml:mrow></mml:mrow> <mml:mrow><mml:mtext>III</mml:mtext></mml:mrow> </mml:msup> </mml:mrow> <mml:annotation>$^{\text{III}}$</mml:annotation></mml:semantics> </mml:math> (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.