O-atom transfer to Fe-n(+) clusters (n=2-10) from O-2, N2O and CO2: ''Microoxides of iron''

We report on the gas phase reactions of small Fe-n(+) clusters (n=2-10) with O-2, N2O and CO2 in an FT-ICR mass spectrometer. Under our experimental conditions, clusters of all sizes reacted readily with O-2 and all but the dimer reacted with N2O. Only the smallest Fe-n(+) clusters (n=2-4) appeared to activate CO2. For all X-O molecules (X=O,N-2,CO), reaction pathways were observed that include the transfer of O atoms. In addition, the reactions with O-2 and N2O were accompanied by the loss of one or two Fe atoms. Thermochemical considerations based upon the well-known X-O bond energies were used to calculate FenO+ bond dissociation energies (BDEs) for sizes n=2-6; these amount to roughly 550 kJmol(-1) and thus are considerably higher than the BDE of the Fe-O+ ion. All oxidation reactions of the Fe-n(+) clusters (n=2-6) studied in more detail were terminated by products of FexOx+ stoichiometry (x=1-4). These ''microoxides of iron'' are not able to activate any further X-O bonds. Secondary reactions of FexOx+ clusters with C6H6, C2H4 and NH, were investigated for two selected sizes (x=2,3) and compared with reactions of the naked Fe-n(+) clusters.