In:
European Journal of Inorganic Chemistry, Wiley, Vol. 2006, No. 21 ( 2006-11), p. 4426-4441
Abstract:
A group of ten quinonoid‐bridged diruthenium(II) complexes [(aap) 2 Ru II (μ‐BL 1 2– )Ru II (aap) 2 ](ClO 4 ) 2 , [ 1a – 1c ](ClO 4 ) 2 and [(pap) 2 Ru II (μ‐BL n 2– )Ru II (pap) 2 ](ClO 4 ) 2 [ 2 – 8 ](ClO 4 ) 2 [aap = 2‐arylazopyridine, NC 5 H 4 –N=N–C 6 H 4 (R) {R = H (pap) [ 1a ](ClO 4 ) 2 , m ‐Me [ 1b ](ClO 4 ) 2 , m ‐Cl [ 1c ](ClO 4 ) 2 }; BL 2– = 5,8‐dioxido‐1,4‐napthoquinone (BL 1 2– ), 2,3‐dichloro‐5,8‐dioxido‐1,4‐napthoquinone (BL 2 2– ), 6,11‐dioxido‐5,12‐naphthacenedione (BL 3 2– ), 1,4‐dioxido‐9,10‐anthraquinone (BL 4 2– ), 2,3‐dimethyl‐1,4‐dioxido‐9,10‐anthraquinone (BL 5 2– ), 6,7‐dichloro‐1,4‐dioxido‐9,10‐anthraquinone (BL 6 2– ), 1,4‐diimino‐9,10‐anthraquinone (BL 7 2– ), 1,5‐dioxido‐9,10‐anthraquinone (BL 8 2– )] have been synthesized. The crystal structures of [ 1a ](ClO 4 ) 2 · H 2 O and [ 3 ](ClO 4 ) 2 suggest the preferential crystallization of the meso isomer in both cases. The two similar C–O distances in coordinated BL 1 2– [C2–O1/C4–O2 1.278(5)/1.291(4) Å] and BL 3 2– [C2–O1/C4–O2 1.282(7)/1.280(7) Å] in [ 1a ](ClO 4 ) 2 and [ 3 ](ClO 4 ) 2 , respectively, and the corresponding intraring distances suggest a delocalized keto‐enol state of the coordinated BL 2– . [ 1 – 8 ] 2+ exhibit two successive one‐electron oxidation processes and multiple reductions in both CH 3 CN and CH 2 Cl 2 . The first oxidation potential varies substantially depending on a variety of factors associated with BL 2– 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 2.5 × 10 4 –2.6 × 10 5 and 1.7 × 10 3 –1.3 × 10 6 in CH 3 CN and CH 2 Cl 2 , 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 (μ‐BL · – )Ru II } instead of the usually expected alternative mixed‐valence formulation of {Ru II (μ‐BL 2– )Ru III }. Consequently, [ 1 – 7 ] 3+ display intense near‐infrared transitions in the range 1200–1500 nm with a band width at half height (Δ ν 1/2 ) 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 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, {Ru II (μ‐BL · – )Ru III }. [ 1 – 8 ] 2+ exhibit multiple ligand‐based reductions involving coordinated BL 2– 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+ . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Type of Medium:
Online Resource
ISSN:
1434-1948
,
1099-0682
DOI:
10.1002/ejic.v2006:21
DOI:
10.1002/ejic.200600638
Language:
English
Publisher:
Wiley
Publication Date:
2006
detail.hit.zdb_id:
1475009-0
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