Synthesis, molecular structure and solution chemistry of the iridium(III) complex imidazolium [trans(bisimidazole)tetrachloro iridate(III)] (IRIM)

The iridium(III) complex imidazolium [trans(bisimidazole)tetrachloro iridate(III)], (IRIM), isostructural to the well known ruthenium(III) analogue, (ICR), has been prepared and characterised, both in the solid state and in solution, by X-ray diffraction and by a variety of physico-chemical techniques. Single crystal X-ray diffraction studies point out that this complex is isomorphous with ICR and with the rhodium(III) analogue. IRIM is moderately soluble in water and within a physiological phosphate buffer. Electronic spectra in the visible, show that the complex is stable for days at pH 7.4; notably no significant chloride hydrolysis is observed over a period of 24 h at 25°C. Stability of IRIM within a physiological buffer was further tested and confirmed by 1H NMR spectra. The complex is stable toward treatment with either hydrogen peroxide or ascorbic acid or silver nitrate. The chemical behaviour in solution and the reactivity of IRIM are compared to those of ICR; implications of the present results for possible pharmacological applications of IRIM and for a better understanding of the mechanism of action of ICR are discussed.