title: Varying Electronic Structures of Diosmium Complexes from Noninnocently Behaving Anthraquinone-Derived Bis-chelate Ligands.
abstract: The new compounds [(bpy)2Os(II)(μ-L1(2-))Os(II)(bpy)2](ClO4)2 ([1](ClO4)2) and [(pap)2Os(II)(μ-L1(2-))Os(II)(pap)2](ClO4)2 ([2](ClO4)2) (H2L1 = 1,4-dihydroxy-9,10-anthraquinone, bpy = 2,2(/)-bipyridine, and pap = 2-phenylazopyridine) and [(bpy)2Os(II)(μ-L2(•-))Os(II)(bpy)2](ClO4)3 ([3](ClO4)3) and [(pap)2Os(II)(μ-L2(2-))Os(II)(pap)2](ClO4)2 ([4](ClO4)2) (H2L2 = 1,4-diamino-9,10-anthraquinone) have been analytically identified as the meso and rac diastereoisomers, respectively. The paramagnetic [3](ClO4)3 was also characterized by crystal structure determination. In CD3CN solution, [3](ClO4)3 displays rather narrow but widely split (13 > δ > -8 ppm) resonances in the (1)H NMR spectrum, yet no EPR signal was observed down to 120 K. Cyclic voltammetry and differential pulse voltammetry reveal several accessible redox states on oxidation and reduction, showing that the replacement of 1,4-oxido by imido donors causes cathodic shifts and that the substitution of bpy by the stronger π-accepting pap ligands leads to a strong increase of redox potentials. Accordingly, system 3(n) with the lowest (2+/3+) potential was synthetically obtained in the mono-oxidized (3+) form. The (3+) intermediates display small comproportionation constants Kc of about 10(3) and long-wavelength near-infrared absorptions; an EPR signal with appreciable g splitting (1.84, 1.96, and 2.03) was only observed for 4(3+), which exhibits the smallest spin density on the osmium centers. An oxidation state formulation [Os(III)(μ-L(•3-))Os(III)](3+) with some [Os(II)(μ-L(2-))Os(III)](3+) contribution was found to best describe the electronic structures. UV-vis-NIR absorption spectra were recorded for all accessible states by OTTLE spectroelectrochemistry and assigned on the basis of TD-DFT calculations. These results and additional EPR measurements suggest rather variegated oxidation state situations, e.g., the pap ligands competing with the bridge L for electrons, while the oxidation produces mixed spin systems with variable metal/ligand contributions.
authors.affiliation: †Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
authors.forename: Abhishek
authors.initials: A
authors.lastname: Mandal
authors.affiliation: ‡Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany.
authors.forename: Anita
authors.initials: A
authors.lastname: Grupp
authors.affiliation: ‡Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Schwederski
authors.affiliation: ‡Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kaim
authors.affiliation: †Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
authors.forename: Goutam Kumar
authors.initials: GK
authors.lastname: Lahiri
mesh_terms: D000880:Anthraquinones / Q000737:chemistry*; D002614:Chelating Agents / Q000737:chemistry*; D004563:Electrochemistry; D004583:Electrons; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D009992:Osmium / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000880:Anthraquinones; D002614:Chelating Agents; D008024:Ligands; D009942:Organometallic Compounds; D009992:Osmium; C034890:1,4-dihydroxyanthraquinone