| Summary: | Stable, readily available, transition metal cluster carbonyl compounds, such as Os<sub>3</sub>(CO)<sub>12</sub>, Ir<sub>4</sub>(CO)<sub>12</sub>, Rh<sub>6</sub>(CO)<sub>16</sub>, have been shown to easily aggregate into multi-nuclear supraclusters following exposure to pulsed ultraviolet laser radiation (laser desorption ionisation, LDI) in the source region of a mass spectrometer. The aggregation process has been studied from the resulting mass spectra, using both of time-of-flight mass spectrometry (TOF MS) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Larger cluster precursors tend to aggregate via the stepwise addition of whole metal cores, whereas the smaller tri-nuclear osmium cluster can produce supraclusters with variable numbers of metal atoms present. Interestingly, laser desorption/ionisation of Os<sub>3</sub>(CO)<sub>12</sub> leads to the formation of prominent dodecaosmium cluster negative ions, such as [Os<sub>12</sub>(CO)<sub>23</sub>]<sup>-</sup>. As far as we are aware, no homoleptic dodecaosmium carbonyl species has been prepared via traditional synthetic methods, highlighting the future potential of this approach if techniques for stabilising these complexes and isolating them can be developed. The LDI spectra also exhibit prominent metastable decay products, corresponding to evaporative carbonyl ligand loss, a phenomenon known as post-source decay. The rates of metastable decay have then been determined for the mono-isotopic rhodium supraclusters. In addition the transition metal carbonyl precursors used in the aggregation experiments have been studied by electrospray ionisation using quadrupole and Fourier transform ion cyclotron resonance mass spectrometers. In this case clusters require derivatisation with an alkoxide agent to produce a carbomethoxy ligand ([COOCH<sub>3</sub>]<sup>-</sup>) on the cluster, providing them with the necessary charge for mass spectrometric detection. The recently introduced technique of Energy Dependent Electrospray Ionisation mass spectrometry (EDESI-MS) has been used to investigate the relative strengths of the metal-to-carbonyl bonds using a process known as in-source collision-induced dissociation. From this data bond dissociation energies for the sequential removal of carbonyl ligands from the transition metal cluster precursor have been determined. FT-ICR MS experiments confirm the presence of a second decay channel leading to the formation of metal carbonyl hydride species, produced from the activation of the carbomethoxy ligand. Preliminary studies of these coordinatively unsaturated transition metal carbonyls with hydrocarbons have also been carried out.
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