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Please use this identifier to cite or link to this item: http://dspace.library.iitb.ac.in/jspui/handle/100/3041

Title: 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)(2)ru}(2)(mu-bl2-)](n+) (aap=2-arylazopyridine)
Authors: GHUMAAN, S
MUKHERJEE, S
KAR, S
ROY, D
MOBIN, SM
SUNOJ, RB
LAHIRI, GK
Keywords: ruthenium
bridging ligands
radical ions
density functional calculations
epr spectroscopy
Issue Date: 2006
Publisher: WILEY-V C H VERLAG GMBH
Citation: EUROPEAN JOURNAL OF INORGANIC CHEMISTRY,(21)4426-4441
Abstract: A group of ten quinonoid-bridged diruthenium(II) complexes [(aap)(2)Ru-II(mu-BL1 (2-))Ru-II(aap)(2)](ClO4)(2), [1a-1c](ClO4)(2) and [(pap)(2)Ru-II(mu-BLn2-)Ru-II (pap)(2)](ClO4)(2) [2-8](ClO4)(2) [aap = 2-arylazopyridine, NC5H4-N=N-C6H4(R) IR = H (pap) [1a](ClO4)(2), m-Me [1b](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-dioxido1,4-napthoquinone (BL22-), 6,11-dioxido-5,12-naphthacene-dione (BL32-), 1,4-dioxido-9,10-anthraquinone (BL42-) 2,3-dimethyl-1,4-dioxido-9,10-anthraquinone (BL52-), 6,7-dichloro1,4-dioxido-9,10-anthraquinone (BL62-), 1,4-diimino-9,10-anthraquinone (BL72-), 1,5-dioxido-9,10-anthraquinone (BL82-)1 have been synthesized. The crystal structures of [1a](ClO4)(2)center dot 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- [C2-01/C4-O2 1.278(5)/1.291(4) angstrom] and BL32- [C2-O1/C4-O2 1.282(7)/1.280(7) angstrom] 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 (K-c) values in the ranges 2.5x10(4)-2.6 x 10(5) and 1.7 x 10(3)-1.3x10(6) 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 [Ru-II(mu-BL-)Ru-II} instead of the usually expected alternative mixed-valence formulation of {Ru-II(mu-BL2-)Ru-III}. Consequently, [1-7](3+) display intense near-infrared transitions in the range 1200-1500 nm with a band width at half height (Delta(V1/2)) 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 11 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, [Ru-II(mu-BL-)R-III}. [-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+). ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
URI: http://dx.doi.org/10.1002/ejic.200600638
http://dspace.library.iitb.ac.in/xmlui/handle/10054/13836
http://hdl.handle.net/100/3041
ISSN: 1434-1948
Appears in Collections:Review

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