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Issue 12, 2001
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Mononuclear and dinuclear ruthenium(II)/(III) salicylates incorporating azoimine functionalities as ancillary ligands. Synthesis, spectroscopic and electron-transfer properties

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Abstract

Ruthenium–salicylate complexes incorporating azoimine based azopyridine ligands, L, of the type [RuII(L)2(salicylate)] 15 [L = NC5H4N[double bond, length as m-dash]NC6H4(R), R = H, m-Me/Cl or p-Me/Cl] have been synthesized and their spectroelectrochemical aspects investigated. The complexes systematically exhibit two 1e and two 2e oxidation processes and four successive one-electron reductions. The stepwise electrochemical oxidations were followed by electronic and EPR spectral studies on each oxidation step which indicate that the initial one-electron oxidation process corresponds to stereoretentive oxidation of the ruthenium(II) centre to ruthenium(III), [RuIII(L)2(salicylate)]+1++–5++. The second oxidation step corresponds to oxidation of the coordinated salicylate moiety in 1++–5++ to the ruthenium(III)–salicylate semiquinone cationic radical, [RuIII(L)2(salicylate)]2+E. The electrogenerated ruthenium(III) congeners (1++–5++) exhibit rhombic EPR spectra corresponding to distorted octahedral complexes. The electrogenerated semiquinone salicylate radical [RuIII(L)2(salicylate)]2+E undergoes a radical recombination process which leads to formation of antiferromagnetically coupled dimeric species, [(L)2RuIII(X)RuIII(L)2]4+F [(X = O2C(O)C6H4C6H4(O)CO2]. The next two 2e oxidation processes are associated with oxidation of the bridging moiety of the dimeric species [(L)2RuIII(X′)RuIII(L)2]4+G [(X′ = O2C(O)C6H3[double bond, length as m-dash]C6H3(O)CO2] followed by oxidation of the metal centres, [(L)2RuIV(X′)RuIV(L)2]6+H. The chemical oxidation of the complexes 15 by HNO3 leads to formation of dimeric complexes, G, straightaway. The complexes display intense charge-transfer bands in the UV-visible region which have been found to be reasonably blue shifted while moving from 15 to 1++–5++ to F to G.

Graphical abstract: Mononuclear and dinuclear ruthenium(II)/(III) salicylates incorporating azoimine functionalities as ancillary ligands. Synthesis, spectroscopic and electron-transfer properties [ ]

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Publication details

The article was received on 03 Jan 2001, accepted on 12 Apr 2001 and first published on 25 May 2001


Article type: Paper
DOI: 10.1039/B100163I
Citation: J. Chem. Soc., Dalton Trans., 2001,0, 1827-1833
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    Mononuclear and dinuclear ruthenium(II)/(III) salicylates incorporating azoimine functionalities as ancillary ligands. Synthesis, spectroscopic and electron-transfer properties

    R. Samanta, B. Mondal, P. Munshi and G. Kumar Lahiri, J. Chem. Soc., Dalton Trans., 2001, 0, 1827
    DOI: 10.1039/B100163I

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