Infrared spectra and photochemistry of the complex pentacarbonyliron in solid matrices at 4 and 20 K: evidence for formation of the complex tetracarbonyliron

The i.r. spectrum of the complex pentacarbonyliron, [Fe(CO)5], has been recorded in a number of different low-temperature matrices. U.v. photolysis produces new bands in the C–O stretching region; these bands disappear on exposure to longer-wavelength light and are assigned to the tetracarbonyl fragment [Fe(CO)4] plus carbon monoxide. The fragement probably adopts a C3v structure due to Jahn–Teller distortion of the tetrahedron. In an argon matrix the formation of [Fe(CO)4] becomes irreversible after prolonged photolysis: this is due to diffusion through the solid argon of CO molecules.