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

The IR intensities of the CH 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 CH bending and CH stretching IR intensities of the cyclopentadienyl ligand, are reported for several organometallic complexes containing the η5-C5H5M 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 CH bending force constant and to the solid-state structure.