Chemical Tuning of the Electronic Structure in Diruthenium Compounds

This study explores how the electronic structure of mixed valence diruthenium paddlewheel complexes can be controlled through chemical modifications. These compounds exhibit a unique electronic configuration due to the quasidegeneracy of π* and δ* orbitals, making them very attractive for applications in electronic, magnetic, catalytic, and bioinorganic systems. Through synthesis, electrochemical and spectroscopic analyses, and density functional theory (DFT) calculations, we have investigated the impact of axial ligand interactions, equatorial ligand electronic effects, and structural distortions on the molecular orbital diagram, paying special attention to how the δ*-π* gap is modified. In contrast to prior assumptions, our results show that variations in equatorial ligand donor strength shift orbital energies in parallel and, therefore, the observed UV/vis trends with Hammett-type substituents are primarily due to solvent-dependent conformational changes. Overall, our findings highlight the role of axial Ru–Cl interactions and torsion angle modifications in stabilizing spin-admixed or low-spin states, offering new pathways for controlling electronic configurations in bimetallic complexes.