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 iridat e(III)], (IRIM), isostructural to the well known ruthenium(III) analogue, ( ICR), has been prepared and characterised, both in the solid state and in s olution, by X-ray diffraction and by a variety of physico-chemical techniqu es. Single crystal X-ray diffraction studies point out that this complex is isomorphous with ICR and with the rhodium(III) analogue. IRIM is moderatel y 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 degreesC. Stability of IRIM within a physiological buffer was furt her tested and confirmed by H-1 NMR spectra. The complex is stable toward t reatment 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 pharmacol ogical applications of IRIM and for a better understanding of the mechanism of action of ICR are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.