Tuning of redox properties for the design of ruthenium anticancer drugs: Part 2. Syntheses, crystal structures, and electrochemistry of potentially antitumor [RuIII/IICl6-n(azole)n]z (n = 3, 4, 6) complexes

Erwin Reisner, Vladimir B. Arion, Anna Eichinger, Norbert Kandler, Gerald Giester, Armando J L Pombeiro, Bernhard K. Keppler

    Research output: Contribution to journalArticlepeer-review


    A series of mixed chloro-azole ruthenium complexes with potential antitumor activity, viz., mer-[RuIIICl3(azole)3] (B), trans-[RuIIICl2(azole)4]Cl (C), trans-[Ru IICl2(azole)4] (D), and [RuII(azole) 6](SO3CF3)2 (E), where azole = 1-butylimidazole (1), imidazole (2), benzimidazole (3), 1-methyl-1,2,4-triazole (4), 4-methylpyrazole (5), 1,2,4-triazole (6), pyrazole (7), and indazole (8), have been prepared as a further development of anticancer drugs with the general formula [RuCl4(azole)2]- (A). These compounds were characterized by elemental analysis, IR spectroscopy, electronic spectra, electrospray mass spectrometry, and X-ray crystallography. The electrochemical behavior has been studied in detail in DMF, DMSO, and aqueous media using cyclic voltammetry, square wave voltammetry, and controlled potential electrolysis. Compounds B and a number of C complexes exhibit one RuIII/Ru II reduction, followed, at a sufficiently long time scale, by metal dechlorination on solvolysis. The redox potential values in organic media agree with those predicted by Lever's parametrization method, and the yet unknown EL parameters were estimated for 1 (EL = 0.06 V), 3 (EL = 0.10 V), 4 (EL = 0.17 V), and 5 (EL = 0.18 V). The EL values for the azole ligands 1-8 correlate linearly with their basicity (pKa value of the corresponding azolium acid H2L+). In addition, a logarithmic dependence between the homogeneous rate constants for the reductively induced stepwise replacement of chloro ligands by solvent molecules and the RuIII/RuII redox potentials was observed. Lower E1/2 values (higher net electron donor character of the ligands) result in enhanced kinetic rate constants of solvolysis upon reduction. The effect of the net charge on the Ru III/RuII redox potentials in water is tentatively explained by the application of the Born equation. In addition, the pH-dependent electrochemical behavior of trans-[RuCl2(1,2,4-triazole) 4]Cl is discussed. © 2005 American Chemical Society.
    Original languageEnglish
    Pages (from-to)6704-6716
    Number of pages12
    JournalInorganic Chemistry: including bioinorganic chemistry
    Issue number19
    Publication statusPublished - 19 Sept 2005


    • Oxidation
    • Redox potential
    • Reduction (electrochem. properties of ruthenium azole chloro complexes)
    • Solvolysis kinetics (kinetics of chloride ligand substitution with solvent mols. upon electrochem. redn. of ruthenium azole chloro complexes)
    • Heterocyclic compounds Role: CPS (Chemical process), PEP (Physical, engineering or chemical process), PRP (Properties), RCT (Reactant), SPN (Synthetic preparation), PREP (Preparation), PROC (Process), RACT (Reactant or reagent) (nitrogen, five-membered,
    • prepn., crystal structure, electrochem. properties and solvolysis kinetics of ruthenium azole chloro complexes)
    • Crystal structure
    • Molecular structure (of ruthenium azole chloro complexes)
    • ruthenium azole prepn structure electrochem solvolysis kinetic
    • crystal structure ruthenium chloro azole complex


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