Ghumaan, Sandeep ; Sarkar, Biprajit ; Patil, Mahendra P. ; Fiedler, Jan ; Sunoj, Raghavan B. ; Kaim, Wolfgang ; Lahiri, Goutam Kumar (2007) Multiple one-electron oxidation and reduction of trinuclear bis(2,4-pentanedionato)ruthenium complexes with substituted diquinoxalino[2,3-a:2',3'-c]phenazine ligands Polyhedron, 26 (13). pp. 3409-3418. ISSN 0277-5387
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Official URL: http://linkinghub.elsevier.com/retrieve/pii/S02775...
Related URL: http://dx.doi.org/10.1016/j.poly.2007.03.030
Abstract
The complexes (μ3-L1/L2)[Ru(acac)2]3, acac-2,4-pentanedionato, L1=2,3,8,9,14,15-hexachlorodiquinoxalino[2,3-a:2',3'-c]phenazine and L2=2,3,8,9,14,15-hexamethyldiquinoxalino[2,3-a:2',3'-c]phenazine, undergo stepwise one-electron oxidation involving a total of three electrons and stepwise one-electron reduction with three (L2) or four electrons (L1). All reversibly accessible states were characterized by UV-Vis-NIR spectroelectrochemistry. Oxidation leads to mixed-valent intermediates {(μ3-L)[Ru(acac)2]3}+ and {(μ3-L)[Ru(acac)2]3}2+ of which the RuIIIRuIIRuII combinations exhibit higher comproportionation constants Kc than the RuIIIRuIIIRuII states - in contrast to a previous report for the unsubstituted parent systems {(μ3-L3)[Ru(acac)2]3}+/2+, L3 = diquinoxalino[2,3-a:2',3'-c]phenazine. No conspicuous inter-valence charge transfer absorptions were observed for the mixed-valent intermediates in the visible to near-infrared regions. The monocations and monoanions were characterized by EPR spectroscopy, revealing rhombic ruthenium(III) type signals for the former. Electron addition produces ruthenium(II) complexes of the reduced forms of the ligands L, a high resolution EPR spectrum with 14N and 35,37Cl hyperfine coupling and negligible g anisotropy was found for {(μ3-L1)[Ru(acac)2]3}-. DFT calculations of (μ3-L1)[Ru(acac)2]3 confirm several ligand-centered low-lying unoccupied MOs for reduction and several metal-based high-lying occupied MOs for electron withdrawal, resulting in low-energy metal-to-ligand charge transfer (MLCT) transitions.
Item Type: | Article |
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Source: | Copyright of this article belongs to Elsevier Science. |
Keywords: | DFT Calculations; EPR; Radical Complexes; Ruthenium; Electrochemistry; Spectroelectrochemistry |
ID Code: | 19165 |
Deposited On: | 23 Nov 2010 13:23 |
Last Modified: | 17 May 2016 03:46 |
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