Sensitivity of the Valence Structure in Diruthenium Complexes As a Function of Terminal and Bridging Ligands

• Published in: Inorganic chemistry 2014-06, Vol.53 (12), p.6082-6093
• Main Authors: Mandal, Abhishek, Agarwala, Hemlata, Ray, Ritwika, Plebst, Sebastian, Mobin, Shaikh M, Priego, José Luis, Jiménez-Aparicio, Reyes, Kaim, Wolfgang, Lahiri, Goutam Kumar
• Format: Article
• Language: English
• Subjects: 2,2'-Dipyridyl - chemistry; Anthraquinones - chemistry; Crystallography, X-Ray; Electrochemistry; Electron Spin Resonance Spectroscopy; Hydroxybutyrates - chemistry; Ligands; Magnetics; Models, Molecular; Organometallic Compounds - chemistry; Pentanones - chemistry; Ruthenium - chemistry; Spectrophotometry, Ultraviolet
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic500452h

The compounds [(acac)2RuIII(μ-H2L2–)RuIII(acac)2] (rac, 1, and meso, 1′) and [(bpy)2RuII(μ-H2L•–)RuII(bpy)2](ClO4)3 (meso, [2](ClO4)3) have been structurally, magnetically, spectroelectrochemically, and computationally characterized (acac– = acetylacetonate, bpy = 2,2′-bipyridine, and H4L = 1,4-diamino-9,10-anthraquinone). The N,O;N′,O′-coordinated μ-H2L n– forms two β-ketiminato-type chelate rings, and 1 or 1′ are connected via NH···O hydrogen bridges in the crystals. 1 exhibits a complex magnetic behavior, while [2](ClO4)3 is a radical species with mixed ligand/metal-based spin. The combination of redox noninnocent bridge (H2L0 → → → →H2L4–) and {(acac)2RuII} → →{(acac)2RuIV} or {(bpy)2RuII} → {(bpy)2RuIII} in 1/1′ or 2 generates alternatives regarding the oxidation state formulations for the accessible redox states (1 n and 2 n ), which have been assessed by UV–vis–NIR, EPR, and DFT/TD-DFT calculations. The experimental and theoretical studies suggest variable mixing of the frontier orbitals of the metals and the bridge, leading to the following most appropriate oxidation state combinations: [(acac)2RuIII(μ-H2L•–)RuIII(acac)2]+ (1 +) → [(acac)2RuIII(μ-H2L2–)RuIII(acac)2] (1) → [(acac)2RuIII(μ-H2L•3–)RuIII(acac)2]−/[(acac)2RuIII(μ-H2L2–)RuII(acac)2]− (1 –) → [(acac)2RuIII(μ-H2L4–)RuIII(acac)2]2–/[(acac)2RuII(μ-H2L2–)RuII(acac)2]2– (1 2–) and [(bpy)2RuIII(μ-H2L•–)RuII(bpy)2]4+ (2 4+) → [(bpy)2RuII(μ-H2L•–)RuII(bpy)2]3+/[(bpy)2RuII(μ-H2L2–)RuIII(bpy)2]3+ (2 3+) → [(bpy)2RuII(μ-H2L2–)RuII(bpy)2]2+ (2 2+). The favoring of RuIII by σ-donating acac– and of RuII by the π-accepting bpy coligands shifts the conceivable valence alternatives accordingly. Similarly, the introduction of the NH donor function in H2L n as compared to O causes a cathodic shift of redox potentials with corresponding consequences for the valence structure.