INFRARED SPECTROSCOPIC CHARACTERIZATION OF CHROMIUM CARBONYL SPECIES FORMED BY ULTRAVIOLET PHOTOREDUCTION OF SILICA-SUPPORTED CHROMIUM(VI) IN CARBON-MONOXIDE

The chromium carbonyl species that form during ultraviolet (UV) photor eduction of Cr6+/SiO2 in (CO)-C-12-O-16 and (CO)-C-13-O-16 were analyz ed by Fourier transform infrared spectroscopy (FTIR). Four carbonyl sp ecies were identified: linear Cr4+(CO), mer-Cr2+(CO)(3), linear Cr2+(C O)(2) and Cr-2(CO)(2) (band at 2099 cm(-1)). The linear Cr4+(CO) band at 2206 cm(-1), formed at short UV exposures, increased to a maximum a nd decreased at long UV exposures. Both the mer-Cr2+(CO)(3), with band s at 2212, 2190, and 2178 cm(-1), and linear Cr2+(CO), with a band at 2184 cm(-1), were present at all UV exposures. The IR bands arising fr om these two species were isolated during isothermal evacuation. The o xidation state of the photoformed Cr2+ species was assigned by compari ng the IR bands following thermal reduction of Cr6+/SiO2 in CO to thos e formed following photoreduction.