Isomeric Diruthenium Complexes of a Heterocyclic and Quinonoid Bridging Ligand: Valence and Spin Alternatives for the Metal/Ligand/Metal Arrangement

5,7,12,14-Tetraazapentacene-6,13-quinone (L) reacts with 2 equiv of [Ru­(acac)₂(CH₃CN)₂] to form two linkage isomeric bis­(chelate) compounds, [{Ru^II(acac)₂}₂(μ-L)], blue <b>1</b>, with 5,6;12,13 coordination and violet <b>2</b> with 5,6;13,14 coordination. The linkage isomers could be separated, structurally characterized in crystals as <i>rac</i> diastereomers (ΔΔ/ΛΛ), and studied by voltammetry (CV, DPV), EPR, and UV–vis–NIR spectroelectrochemistry (<i>meso</i>-<b>1</b>, <i>rac</i>-<b>2</b>). DFT and TD-DFT calculations support the structural and spectroscopic results and suggest a slight energy preference (Δ<i>E</i> = 263 cm^–1) for the <i>rac</i>-isomer <b>1</b> as compared to <b>2</b>. Starting from the Ru^II–(μ-L⁰)–Ru^II configurations of <b>1</b> and <b>2</b> with low-lying metal-to-ligand charge transfer (MLCT) absorptions, the compounds undergo two reversible one-electron oxidation steps with open-shell intermediates <b>1</b>^<b>+</b> (<i>K</i>_c = 4 × 10⁴) and <b>2</b>^<b>+</b> (<i>K</i>_c = 6 × 10⁵). Both monocations display metal-centered spin according to EPR, but the DFT-calculated spin densities suggest a Ru^III(μ-L^•–)­Ru^III three-spin situation with opposite spin density at the bridging ligand for the <i>meso</i> form of <b>1</b>⁺, estimated to lie 1887 cm^–1 lower in energy than <i>rac</i>-<b>1</b>^<b>+</b>, which is calculated with a Class II mixed-valent situation Ru^III–(μ-L⁰)–Ru^II. A three-spin arrangement Ru^III–(μ-L^•–)–Ru^III with negative spin density at one metal site is suggested by DFT for <i>rac</i>-<b>2</b>^<b>+</b> which is more stable by Δ<i>E</i> = 890 cm^–1 than <i>rac</i>-<b>1</b>^<b>+</b>. Reduction of <b>1</b> or <b>2</b> (<i>K</i>_c = 10⁷–10⁸) occurs mainly at the central bridging ligand with notable contributions (30%) from the metals in <b>1</b>^<b>–</b> and <b>2</b>^<b>–</b>. The mixed-valent Ru^III(μ-L)­Ru^II versus radical-bridged Ru^III(μ-L^•–)­Ru^III alternative is discussed comprehensively in comparison with related valence-ambiguous cases