Ghumaan, Sandeep ; Mukherjee, Sriparna ; Kar, Sanjib ; Roy, Dipankar ; Mobin, Shaikh M. ; Sunoj, Raghavan B. ; Lahiri, Goutam Kumar (2006) An experimental and density functional theory approach towards the establishment of preferential metal- or ligand-based electron-transfer processes in large quinonoid-bridged diruthenium complexes [{(aap)2Ru}2(μ-BL2-)]n+ (aap = 2-arylazopyridine) European Journal of Inorganic Chemistry, 2006 (21). pp. 4426-4441. ISSN 1434-1948
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Official URL: http://onlinelibrary.wiley.com/doi/10.1002/ejic.20...
Related URL: http://dx.doi.org/10.1002/ejic.200600638
Abstract
A group of ten quinonoid-bridged diruthenium(II) complexes [(aap)2RuII(μ-BL12-)RuII(aap)2](ClO4)2, [1a-1c](ClO4)2 and [(pap)2RuII(μ-BLn2-)RuII(pap)2](ClO4)2 [2-8](ClO4)2 [aap = 2-arylazopyridine, NC5H4-N=N-C6H4(R) {R = H (pap) [1a](ClO4)2, m-Me [1b](ClO4)2, m-Cl [1c](ClO4)2}; BL2- = 5,8-dioxido-1,4-napthoquinone (BL12-), 2,3-dichloro-5,8-dioxido-1,4-napthoquinone (BL22-), 6,11-dioxido-5,12-naphthacenedione (BL32-), 1,4-dioxido-9,10-anthraquinone (BL42-), 2,3-dimethyl-1,4-dioxido-9,10-anthraquinone (BL52-), 6,7-dichloro-1,4-dioxido-9,10-anthraquinone (BL62-), 1,4-diimino-9,10-anthraquinone (BL72-), 1,5-dioxido-9,10-anthraquinone (BL82-)] have been synthesized. The crystal structures of [1a](ClO4)2.H2O and [3](ClO4)2 suggest the preferential crystallization of the meso isomer in both cases. The two similar C-O distances in coordinated BL12- [C2-O1/C4-O2 1.278(5)/1.291(4) Å] and BL32- [C2-O1/C4-O2 1.282(7)/1.280(7) Å] in [1a](ClO4)2 and [3](ClO4)2, respectively, and the corresponding intraring distances suggest a delocalized keto-enol state of the coordinated BL2-. [1-8]2+ exhibit two successive one-electron oxidation processes and multiple reductions in both CH3CN and CH2Cl2. The first oxidation potential varies substantially depending on a variety of factors associated with BL2-and follows the order: [8]2+ » [2]2+ > [6]2+ > [1a]2+≥[4]2+ > [3]2+ > [5]2+ » [7]2+. The separation in potentials between the successive oxidation processes translates to comproportionation constant (Kc) values in the ranges 2.5 × 104-2.6 × 105 and 1.7 × 103-1.3 × 106 in CH3CN and CH2Cl2, respectively. The intermediate paramagnetic species [1-8]3+ systematically exhibit closely spaced rhombic or axial-type EPR spectra at 77 K corresponding to g values close to the free-electron value of 2.0023, thereby suggesting a radical complex formulation of {RuII(μ-BL.-)RuII} instead of the usually expected alternative mixed-valence formulation of {RuII(μ-BL2-)RuIII}. Consequently, [1-7]3+ display intense near-infrared transitions in the range 1200-1500 nm with a band width at half height (Δν½) of 1900-3800 cm-1 which is lower than the calculated value of 3800-4600 cm-1 obtained using the Hush formula for a localized class II mixed-valence system. Electrogenerated EPR-inactive second-step oxidized species [1-8]4+ have been described as spin-coupled radical-bridged mixed-valence ruthenium(II)(III) species, {RuII(μ-BL.-)RuIII}. [1-8]2+ exhibit multiple ligand-based reductions involving coordinated BL2-as well as aap. The above preferential metal- or ligand-based accessible electron-transfer processes in the complexes have been further substantiated by DFT calculations on the geometry-optimized structure of [1a]2+.
Item Type: | Article |
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Source: | Copyright of this article belongs to John Wiley and Sons, Inc. |
Keywords: | Ruthenium; Bridging Ligands; Radical Ions; Density Functional Calculations; EPR Spectroscopy |
ID Code: | 19136 |
Deposited On: | 23 Nov 2010 13:27 |
Last Modified: | 26 Feb 2011 04:19 |
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