PHOTOREDOX CHEMISTRY OF IODOMERCURATE(II) COMPLEXES IN ACETONITRILE

The stepwise formation constants of the kinetically labile iodomercurates(II) in acetonitrile are relatively high; even for the tetraiodo complex a value of 1220 was determined. Ligand-to-metal charge transfer transitions of different energies and intensities feature the ultraviolet spectra of these compounds. Photolysis of their CH3CN solution results in the formation of Hg(I) and I. or I2- as primary products. The quantum yields of this reaction are 0.8 and 0.41 for HgI3- and HgI42-, respectively, at 355 nm excitation in a deaerated system. Due to the very efficient back reaction HgI2 does not undergo permanent photoredox change, while irradiation of tri-and tetraiodomercurate(II) complexes leads to the accumulation of I2 and I3-. The efficiencies of these overall reactions are rather low (0.07 and 0.02 at 333 nm), compared to the primary quantum yields, because of the fast reconversion.