Carbonyl clusters mass spectra

Similar experiments on a large number of transition metal carbonyls have shown that this process favors dissociation to and detection of metal clusters or atoms. Since most metal-(CO)n photofragments are themselves subject to efficient dissociation, MPI experiments do not identify the primary photoproducts. This situation contrasts sharply with electron impact ionization where the parent ion is usually formed and daughter ions are seen as a result of parent ion fragmentation. Figure 4 shows the electron impact mass spectrum of Mn2(C0) Q (33). for comparison with the MPI mass spectrum of Figure 3. 

The green Mo3 cluster shows three H resonances in the ratio 1 10 5. The peak of area one (58.9, CDC13) is in the range associated with metal formyls (34) and there are two equivalent and one different Cp groups. The carbonyl stretches of the M03 cluster occur at 1763 and 1713 cm-1. The mass spectrum shows a series of Mo3 patterns starting at m/e = 580 with consecutive loss of 5 carbonyls, and a series of strong peaks due to dipositive ions corresponding to the monopositive series 524, 496, 468, and 440. 

Fig. 1.32. Production mass spectrum obtained after reaction of a mass-selected Ni4 cluster with approximately 3 x 10 mbar of CO. The geometric structure of the saturated carbonyl cluster proposed on the basis of simple electron count-structure correlations is also displayed [31]...

The recently reported carbide clusters of ruthenium, Rue(CO)i7C and Ru6(CO)i4(arene)C (211), provided a good example of the power of mass spectrometry as an analytical tool. The appearance of the ions Rug(CO) C+ (n = 0-17) provided a clear differentiation between Rue(CO)i7C and another proposed formula Rug(CO)i8 (324). The first carbonyl oxide cluster 0s3(C0)i2 0s04 was characterized by its mass spectrum. The ions 0s404(C0),i+ (n = 0-12) occur in high abundance and the tetranu clear cluster does not rupture until all CO groups are lost (219,220). Other clusters which have been characterized by mass spectrometry include Os3(CO)io(OMe)2 (217), Ru3(CO)i2Xg (X = Cl, Br, I) (212),... 

---