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The reactions of a mother solution of RuCl(3) with benzimidazole derivatives 2-(2'-pyridyl)benzimidazole (2,2'-PyBIm, L(1)) and 2-hydroxymethylbenzimidazole (2-CH(2)OHBIm, L(2)) yielded three novel ruthenium complexes: (H(2)L(1))(2)[Ru(III)Cl(4)(CH(3)CN)(2)](2)[Ru(IV)Cl(4)(CH(3)CN)(2)]·2Cl·6H(2)O (1), mer-[Ru(III)Cl(3)L(1)(CH(3)CN)]·L(1)·3H(2)O (2), and (HL(2))(4)[Ru(IV)Cl(6)]·2Cl·4H(2)O (3). The isolated compounds were characterised by elemental analyses, UV-Vis and IR spectroscopy, and magnetic measurements. The nature of the ligands bound to the metal ions of these compounds and the experimental conditions significantly influenced the ruthenium complexes in different oxidation states. The N,N-donor ligand bound to the metal centre is a recognised stabiliser of the +III state of ruthenium, whereas the lack of ligand coordination promotes the formation of a mixed (Ru(III)/Ru(IV)) complex. In the case of complex 3, the absence of a N,O-donor ligand in the coordinate sphere facilitates the formation of the compound in a higher oxidation state. X-ray single crystal analyses revealed an octahedral geometry in each of the complexes. The crystal structure of ruthenium complexes is formed by a network of intermolecular classical and unconventional (C-H···π) hydrogen bonds. The most interesting feature of the supramolecular architecture of complexes is the existence of a very rare Cl(-)···π interaction and π···π stacking, which also contribute to structural stabilisation. Ruthenium compounds 2 and 3 behave as paramagnets with an octahedral geometry, corresponding to the presence of one or two unpaired electrons, respectively. The cyclic voltammetric data of complex 2 show three one-electron redox processes. The first redox couple is reversible, whereas the two other couples have a quasi-reversible nature. In the case of complex 3, two redox couples are reversible and the electrode processes are connected with exchange of one electron.

A novel single site Mn(II) complex was successfully synthesized and tested in the aqueous disproportionation of hydrogen peroxide. The complex was found to be stable (HR-XAS) and exhibits catalase-like activity in neutral pH. Theoretical calculations suggested a reaction mechanism involving two complexes, changes in metal oxidation state and proton shuttling.

The application of coordination chemistry in the light of nanotechnology is a rapidly developing research field in medicine. Bismuth complexes have been widely and willingly used in biomedicine with satisfactory therapeutic effects, mostly in Helicobacter pylori eradication, but also as potential anti-microbial and anti-leishmanial agents. Additionally, in recent years, an application of bismuth-based compounds as potent anticancer drugs has also been studied extensively. Therefore, in this review, we want to highlight a number current problems connected with: (1) characterization of bismuth complexes based on thiosemicarbazone, hydrazone, and dithiocarbamate classes of ligands as potential chemotherapeutics, (2) pioneering research on application of bismuth-based nanoparticles and nanodots for radiosensitization, and (3) research challenges in using bismuth radionuclides in targeted radioimmunotherapy.

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