Bridging carbonyl groups in transition metal clusters; A normal coordinateanalysis

The suggestion that the infrared active v(CO) features associated with the bridging carbonyls in transition metal cluster carbonyls may provide struct ural information is examined by a normal coordinate analysis. The species s tudied are four tetranuclear clusters, each containing an equilateral trian gle of metal atoms, the edges of which are spanned by carbonyl groups. Isot opically enriched species have been prepared and are included in the study so that the problem is well over-determined. Excellent agreement between ca lculated spectra and those observed under high resolution, including relati ve intensity data, is obtained. The results confirm that it is reasonable t o expect that the features associated with bridging carbonyls in such compo unds may provide structural information.