The charge distribution on metal-bonded cyclopentadienyl rings from infrared intensities

The IR intensities of the CH vibrational modes of a hydrocarbon fragment bonded to a metal atom are a useful probe to evaluate the charge distribution on the fragment. The values of R, the ratio of the overall CH bending and CH stretching IR intensities of the cyclopentadienyl ligand, are reported for several organometallic complexes containing the h5-C5H5M unit. The parameter R is related to several properties of the complexes, such as the ionic charge, the nature of the metal and of the ancillary ligands, the CH bending force constant and to the solid-state structure.