SPECTROSCOPIC OBSERVATION OF COUPLED METAL-LIGAND VIBRATIONAL-MODES IN THE LUMINESCENCE SPECTRUM OF TRANS-[REO2(1-METHYLIMIDAZOLE)(4)]I

Near-infrared luminescence with resolved vibronic structure between 70 0 and 1200 nm has been observed from the title compound at 15 K. Its e mitting state is lower in energy by more than 3000 cm(-1) than those i n other trans-dioxo compounds of rhenium(V). The vibrational modes for ming the resolved structure are the totally symmetric Re-O and Re-N(im idazole) stretching vibrations. The intensity distribution within the vibronic progressions can be rationalized only qualitatively with a ha rmonic model (coupling = 0 in the diagram), but it is quantitatively c alculated by including nonzero coupling between the normal coordinates for the metal-ore and metal-imidazole vibrational modes, an effect ob served and analyzed for the first time in a coordination compound.