Reactivity and characterization of transition-metal carbonyl clusters using UV laser desorption mass spectrometry

The positive and negative ion ultraviolet laser desorption time-of-flight m ass spectra of [Ru-3(CO)(12)] have been recorded, using a 337 nm N-2 laser, over a range of experimental conditions. In the negative ion spectra the p arent ion is not observed, but peaks corresponding to the trinuclear cluste r ions [Ru-3(CO)(11)](-) [Ru-3(CO)(10)](-) and [Ru-3(CO)(9)](-), derived di rectly from the parent by the successive loss of one to three CO groups, ar e present. In addition, peaks corresponding to cluster ions with nucleariti es ranging from 2 to 11 are observed. The higher mass clusters in the negat ive ion spectra have considerably greater intensities than the trinuclear c lusters, suggesting that stable higher nuclearity clusters have been genera ted during the laser desorption process. It would appear that, in general, these correspond to the series of carbonyl clusters derived from the therma l decomposition of [Os-3(CO)(12)] that have yet to be isolated for rutheniu m. In the positive ion spectra peaks corresponding to [Ru-3(CO)(13)](+), [R u-3(CO)(12)](+) [Ru-3(CO)(11)](+), and [Ru-3(CO)(10)](+) are observed. Othe r peaks corresponding to species containing from four to six ruthenium atom s are also present. In addition, the appearance of peaks corresponding to t he dinuclear species [Ru-2(CO)(8)](+) and [Ru-2(CO)(9)](+) indicates that s ome fragmentation takes place. Representative mass spectra are shown and so me mechanistic proposals are given concerning the possible ionization mecha nisms and the effect these have on the clustering processes. Related phenom ena have been observed in similar experiments on [Fe-3(CO)(12)] and [Os-3(C O)(12)], and their spectra are compared with those of [Ru-3(CO)(12)].