Patra, Srikanta ; Mondal, Biplab ; Sarkar, Biprajit ; Niemeyer, Mark ; Lahiri, Goutam Kumar (2003) First example of μ3-sulfido bridged mixed-valent triruthenium complex triangle RuIII2RuII(O,O-acetylacetonate)3(μ -O,O,μ-C-acetylacetonate)3(μ3-S) (1) incorporating simultaneous O,O- and γ -C-bonded bridging acetylacetonate units. Synthesis, crystal structure, and spectral and redox properties Inorganic Chemistry, 42 (4). pp. 1322-1327. ISSN 0020-1669
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Official URL: http://pubs.acs.org/doi/abs/10.1021/ic026221i
Related URL: http://dx.doi.org/10.1021/ic026221i
Abstract
The reaction of mononuclear ruthenium precursor [RuII(acac)2(CH3CN)2] (acac = acetylacetonate) with the thiouracil ligand (2-thiouracil, H2L1 or 6-methyl -2-thiouracil, H2L2) in the presence of NEt3 as base in ethanol solvent afforded a trinuclear triangular complex Ru3(O,O-acetylacetonate)3 (μ-O,O,γ-C-acetylacetonate)3(μ3-sulfido) (1). In 1, each ruthenium center is linked to one usual O,O-bonded terminal acetylacetonate molecule whereas the other three acetylacetonate units act as bridging functions:γ each bridges two adjacent ruthenium ions through the terminal O,O-donor centers at one end and via the γ-carbon center at the other end. Moreover, there is a μ3-sulfido bridging in the center of the complex unit, which essentially resulted via the selective cleavage of the carbon-sulfur bond of the thiouracil ligand. In diamagnetic complex 1, the ruthenium ions are in mixed valent RuIIIRuIIIRuII state, where the paramagnetic ruthenium(III) ions are antiferromagnetically coupled. The single crystal X-ray structure of 1 showed two crystallographically independent C3-symmetric molecules, Ru3(O,O-acetylacetonate)3(μ-O,O,γ-C-acetylacetonate)3(μ 3-S) (1), in the asymmetric unit. Bond distances of both crystallographically independent molecules are almost identical, but there are some significant differences in bond angles (up to 6°) and interplanar angles (up to 8°). Each ruthenium atom exhibits a distorted octahedral environment formed by four oxygen atoms, two from each of the terminal and bridging acetylacetonate units, oneγ -carbon of an adjacent acetylacetonate ligand, and the sulfur atom in the center of the complex. In agreement with the expected 3-fold symmetry of the complex molecule, the 1H and 13C NMR spectra of 1 in CDCl3 displayed signals corresponding to two types of ligand units. In dichloromethane solvent, 1 exhibited three metal center based successive quasireversible redox processes, RuIIIRuIIIRuIII-RuIIIRuIIIRuII (couple I, 0.43 V vs SCE); RuIIIRuIIIRuIV-RuIIIRuIIIRuIII (couple II, 1.12 V); and RuIIIRuIIIRuII-RuIIIRuIIRuII (couple III, -1.21 V). However, in acetonitrile solvent, in addition to the three described couples [(couple I), 0.34 V; (couple II), 1.0 V; (couple III), -1.0], one irreversible oxidative response (RuIIIRuIIIRuIV → RuIIIRuIVRuIV or oxidation of the coordinated sulfide center) appeared at Epa, 1.50 V. The large differences in potentials between the successive couples are indicative of strong coupling between the ruthenium ions in the mixed-valent states. Compound 1 exhibited a moderately strong charge-transfer (CT) transition at 654 nm and multiple ligand based intense transitions in the UV region. In the RuIIIRuIIIRuIII (1+) state, the CT band was slightly blue shifted to 644 nm; however, the CT band was further blue shifted to 520 nm on two-electron oxidation to the RuIIIRuIIIRuIV (12+) state with a reduction in intensity.
| Item Type: | Article |
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| Source: | Copyright of this article belongs to American Chemical Society. |
| ID Code: | 88407 |
| Deposited On: | 28 Mar 2012 09:59 |
| Last Modified: | 28 Mar 2012 09:59 |
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