Synthesis and Characterization of an Azido-Bridged Dinuclear Ruthenium(II) Polypyridylamine Complex Forming a Mixed-Valence State

We have synthesized a mononuclear ruthenium­(II) azido complex (1) and a dinuclear ruthenium­(II) μ-azido complex (2) having N,N-bis­(2-pyridylmethyl)-N-bis­(2-pyridyl)­methylamine (N4Py) as a pentadentate ancillary ligand. In the crystal structure of 2, intramolecular π–π stacking was found between the pyridine rings of the two different N4Py ligands, contributing to stabilize the dinuclear μ-azido structure. π donation from the HOMO π* orbital of the μ-azido ligand to the Ru–N­(pyr) bond increases the bond order between the terminal and central N atoms in the μ-azido ligand to strengthen the N–N bonds of the μ-azido ligand. The μ-azido complex 2 was revealed to exhibit a stepwise oxidation behavior in CH3CN to afford a RuII–μ-azido–RuIII mixed-valence (MV) state upon one-electron oxidation. The MV state of one-electron-oxidized 2 was categorized in the Robin–Day class II with the electronic coupling constant (Hab) of 570 cm–1.