Photodissociation mass spectrometry of trinuclear carbonyl clusters M-3(CO)(12) (M = Fe, Ru, Os)

Photodissociation of trinuclear carbonyl cluster compounds of Fe, Ru and Os was studied by recording the mass spectra produced from laser ablation of the cluster compounds. Under the experimental conditions, dissociation of the cluster compounds is very exten sive, but the dissociation pathway of the osmium cluster is different from those of the iron and ruthenium clusters. The iron and ruthenium clusters not only lost their carbonyl ligands, but their cluster cores were also fragmented. As the osmium cluster dissoci ated, it ejected three pairs of oxygen atoms, in sequence, before losing the carbonyl ligands, but the trinuclear osmium core did not fragment. This specific dissociation scheme of the osmium cluster reveals its special structural stability. Not only does it have stronger metal-metal bonds, but also a relatively stable coordination bond formed between osmium and carbonyl ligands. In addition, differ ent distributions of positive and negative fragment ions were observed in the experiment. This difference is interpreted as the result of different stabilities of their electronic structures.