Solid-state metal carbonyls. Part 3.—An infrared study of Fe2(CO)9, tri-µ-carbonyl(hexacarbonyl)di-iron(0)

Abstract

I.r. data at liquid-nitrogen temperature have been collected for Fe₂(CO)₉ in the 20–2500 cm^–1 interval using polycrystalline samples, and supplemented by i.r.-reflectance data in the 200–2500 cm^–1 region. Using, in addition, extant Raman data, a complete assignment is deduced for all the optically active modes of the molecule. The ν(CO)_t, ν(Fe—C)_t and δ(FeCO)_t(t = terminal) modes all show clearly that there is substantial coupling between the two sets of terminal carbonyl groups. Fe—Fe bond stretching is considered to make a major contribution to the Raman bands at 260 and 237 cm^–1.