Bridging carbonyl groups in transition metal clusters; A normal coordinate analysis

The suggestion that the infrared active v(CO) features associated with the bridging carbonyls in transition metal cluster carbonyls may provide structural information is examined by a normal coordinate analysis. The species studied are four tetranuclear clusters, each containing an equilateral triangle of metal atoms, the edges of which are spanned by carbonyl groups. Isotopically enriched species have been prepared and are included in the study so that the problem is well over-determined. Excellent agreement between calculated spectra and those observed under high resolution, including relative intensity data, is obtained. The results confirm that it is reasonable to expect that the features associated with bridging carbonyls in such compounds may provide structural information.