The v(CO) vibrational spectra of planar transition metal carbonyl clusters

The v(CO) vibrational spectra of planar transition cluster carbonyls containing M(CO)₄ groups are studied. It is possible to anticipate qualitatively, both for the infrared and Raman, the band intensity changes associated with increasing metallic nature of the cluster. These enable a unification of the band patterns shown by the species reported. As for (idealized) spherical clusters, the spherical harmonic model (SHM), suitably modified, becomes of more general applicability as cluster size increases, although for smaller species the tensor harmonic model (THM) makes a contribution.