The infrared spectra of metal carbonyl compounds. Part II. C18O exchange studies on cis-Fe(CO)4I2
The exchange of C18O with the CO groups of cis-Fe(CO)4I2 has been studied by following the variation of the i.r. spectrum in the CO stretching region with time. The CO stretching frequencies for the isotropically substituted species which might have been produced have been calculated and the spectra observed experimentally assigned. From this information the CO stretching frequencies of the parent molecule have been assigned. On the basis of these results and those derived from studies of 13CO (naturally-occurring) species of Fe(CO)4Br2 more accurate force constants (Cotton–Kraihanzel parameters) for cis-Fe(CO)4I2 and cis-Fe(CO)4Br2 have been calculated. The combination spectrum for Fe(CO)4I2 has been measured and provides further evidence for the formation of trans-Fe(CO)4I2 when the cis-isomer is exposed to light.