The interpretation of the terminal v(CO) spectra of some tetranuclear carbonyl clusters

The recently suggested spherical (SHM) and tensor (THM) harmonic models are applied to the interpretation of the terminal v(CO) spectra of twenty six tetrahedral transition metal clusters containing between four and twelve terminal carbonyl groups. Although the SHM is perhaps the more generally relevant, there are species for which the THM is appropriate as a first approximation. The distinction between the two appears to be associated with a disruption of the band structure of the cluster either by the introduction of heterometal atoms or by the presence of a group - acetate ester, halide or hydride - presumably acting as an electronegative substituent.