Synthetic, Electrochemical, DFT, and Synchrotron X-ray Charge-Density Studies on Oxo-centered Triruthenium Clusters Supported by Electron-Withdrawing Carboxylates

We herein report the synthesis, characterizations, and synchrotron X-ray charge-density studies of oxo-centered triruthenium(II,III,III) clusters [Ru₃O(CHCl₂COO)₆(py)₃] (<b>1</b>) and [Ru₃O(CHCl₂COO)₆(CO)(py)₂] (<b>2</b>) (py = pyridine). Dichloroacetate was chosen for its large scattering factor of the Cl atom, and its electron-withdrawing nature results in significant stabilization of the targeted lower-valent Ru₃^II,III,III state in the cluster framework. Multipole analysis revealed that the difference in electron populations between two crystallographically independent Ru centers is small for <b>1</b> (Δ = 0.30 e) but large for <b>2</b> (Δ = 1.46 e). Remarkable differences between <b>1</b> and <b>2</b> are also found in their static deformation density maps; substantial local charge depletion was found around the central μ₃O atom for <b>1</b>, which is less pronounced for <b>2</b>. According to the topological characterization of Ru-μ₃O bonds associated with the bond critical point, bcp, the electron density, ρ_bcp, is in the range of 0.79-0.89 e Å^-3, and the total energy density, <i>H</i>_bcp, is in the range of -0.21 to -0.05 hartree Å^-3. These findings represent the first charge-density distribution analysis of mixed-valence multinuclear Ru complexes including comparison between 3d and 4d transition-metal systems.