The infrared spectra of metal carbonyl compounds. Part II. C18O exchange studies on cis-Fe(CO)4I2

Abstract

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.