O‐Atom Transfer to Fe⁺_n Clusters (n = 2–10) from O₂, N₂O and CO₂: “Microoxides of Iron”

Abstract

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

Formation, Structure, and Reactivity of Gaseous Ni2O2+

“…For NiO + , unity efficiency is already reached in the reaction with ethane; the increased reactivity of NiO + is also reflected in its ability to activate methane 3. Attenuation of reactivity associated with the transition from mononuclear to dinuclear transition‐metal oxides is a general trend also observed for manganese11 and iron 12,13. The lower charge densities of the cluster ions and their higher degrees of valence saturation are likely reasons for the more moderate reactivities 37.…”

“…Nonetheless, the number of reactivity studies on M m O n + clusters still is limited 8. So far, research activities have focused on V m O n + ,9,10 their heavier homologues Nb m O n + and Ta m O n + ,9 Mn 2 O 2 + ,11 Fe m O n + ,12,13 and Pt m O + 14. In addition, reactions of the dinuclear cluster ions Ti 2 O 2 + and Co 2 O 2 + have been investigated;15,16 however, these studies did not address the problems of C–H bond activation or oxygen‐atom transfer, which are prime challenges in the context of catalysis 17…”

Formation and Reactivity of Gaseous Iron‐Sulfur Clusters

“…Compared with Fe 2 S 2 ϩ , the higher reactivity of Fe 2 O 2 ϩ is also evident from its ability to attack non-activated hydrocarbons such as n-butane. [20,21] Obviously, the metal core cannot fully compensate for the electron deficiency of the O atoms such that the latter exhibit a high affinity for oxidation reactions. For Fe 2 S 2 ϩ , the lower electronegativity of sulfur leads to a better balanced electronic structure in this cluster and a significantly reduced oxidative power.…”

“…Moreover, a comparison with the analogous Fe n O x ϩ ions promised to be most revealing for the dinuclear systems because Fe 2 O 2 ϩ has been studied extensively. [20,21] Ϫ7 mbar], thus again suggesting radiative rather than termolecular relaxation of the association complexes. Compared with H 2 O, the enhanced reactivity of NH 3 reflects its higher basicity that leads to a stronger dative binding which in turn raises the lifetime of the energetic ion-molecule complexes, see above.…”

Intrinsic Mechanisms of Oxidation Reactions as Revealed by Gas-Phase Experiments

“…However, this technique is unique in some respects and the prospects for the gas-phase chemistry of actinides [96] are particularly noteworthy. Other approaches involve the oxidation of pure metal cluster ions in the gas phase [97], but this approach is often associated with degradation of the clusters to smaller, if not even mononuclear entities [98,99]. We have recently introduced a completely different approach based on electrospray ionization of appropriate inorganic precursors and so far have produced several M m O n + clusters for the metals magnesium, vanadium, and iron [46,84,100,101].…”