Intensitätsmessungen an den Carbonylbanden von Eisencarbonyl‐Verbindungen, Kobaltcarbonylen, Nickelcarbonyl sowie Chrom‐, Molybdän‐ und Wolframcarbonyl

The integrated intensities per carbonyl group («specific intensities») of the carbonyl bands of the compounds investigated are from three to seven times higher than those of saturated ketones. Cr(CO) 6 , Mo(CO) 6 and W(CO) 6 have a higher, Ni(CO) 4 has about the same specific intensity as Fe(CO) 5 . Substitution of one or two carbonyls in Fe(CO) 5 by π‐bonded hydrocarbons does not alter the specific intensity of the remaining CO‐groups, but halogen substitution lowers it by a large amount. On a frequency‐intensity diagram the points for the iron compounds lie on a straight line, indicating that influences which lower the intensity raise the frequency and vice versa . Bridging carbonyls have lower intensities than terminal ones. From the measurements on Fe 3 (CO) 12 , it is concluded that this compound does not contain bridging carbonyls and a structure in accord with previous X‐ray work is proposed.