The infrared spectrum of [π-C5H5Fe(CO2)2] is markedly solvent dependent in the 500–700, 1700–2100, and 3500–4000 cm.–1 regions. The spectra can best be explained on the assumption that there are two bridged and one non-bridged isomer present in solutions, and that their proportions vary from solvent to solvent. These suggestions also account for the dipole moment of the compound.