Author :
Amirnasr, Mehdi,Zanella, Andrew W.,Ford, Peter C
Abstract :
The photochemical properties of the iridium (III) ammine complexes Ir(NH***3)***5X**2+ (X- = C1-, Br-.I-). Ir(NH***3)***5L**3+ (L = NH***3, H***2O, CH***3CN, C***oH***5CN), trans - ir(NH***3)***4L***2+. and trans - ir (NH***3)***4(H***2O)l***2+ in aqueous solution are reported and discussed. In general it is observed that photolysis into the ligand-field (LF) absorption band region leads to ligand photoaquations (only) with quantum yields and product distributions independent both of the irradiation wavelength and of whether the solutions are deaerated or air saturated. Since the wavelength range studied included both singlet bands and those assigned as the lowest energy "triplet" absorptions, it is concluded that LF excitation is followed by efficient conversion/intersystem crossing to give a common excited state, the lowest energy "triple" LF state. For those species giving disubstituted products, the stereochemistry is exclusively trans. Irradiation at wavelengths corrsponding to ligand to metal charge-transfer (LMCT) absorption bands also leads predominantly to ligand aquation as the net photoreaction. However, different reaction patterns are noted in areated solutions than in deaerated solutions, suggesting a redox component to this photochemistry. Qualitatively, the photochemistry of the iridium (III) ammine complexes parallels that of the rhodium (III) analogues.
