Competitive Hydrogen-Atom Abstraction versus Oxygen-Atom and Electron Transfers in Gas-Phase Reactions of [X4O10].+(X=P, V) with C2H4

Regioselective Bond-Forming and Hydrolysis Reactions of Doubly Charged Vanadium Oxide Anions in the Gas Phase

The gas-phase reactivity of vanadium-containing dianions, NaV3O92− and its hydrated form H2NaV3O102−, were probed towards sulphur dioxide at room temperature by ion-molecule reaction (IMR) experiments in the collision cell of an ion trap mass spectrometer. The sequential addition of two SO2 molecules to the NaV3O92− dianion leads to the breakage of the stable V3O9 backbone, resulting in a charge separation process with the formation of new V-O and S-O bonds. On the contrary, the H2NaV3O102− hydroxide species reacts with SO2, promoting regioselective hydrolysis and bond-forming processes, the latter similar to that observed for the NaV3O92− reactant anion. Kinetic analysis shows that these reactions are fast and efficient with rate constants of the 10−9 (±30) cm3 s−1 molecule−1 order of magnitude.

Methane selective oxidation to methanol by metal-exchanged zeolites: a review of active sites and their reactivity

A review of the recent progress in revealing the structures, formation, and reactivity of the active sites in Fe-, Co-, Ni- and Cu-exchanged zeolites as well as outlooks on future research challenges and opportunities is presented.

Sulphur dioxide cooperation in hydrolysis reactions of vanadium oxide and hydroxide cluster dianions

Gas-phase hydrolysis takes place due to the synergistic action of SO₂ and vanadium-containing dianions that succeeds in tightening hydrogen bonds.

Catalysis of "outer-phase" oxygen atom exchange reactions by encapsulated "inner-phase" water in {V15Sb6}-type polyoxovanadates

Antimonato polyoxovanadate (POV) cluster compounds {M(en)3}3[V15Sb6O42(H2O) x ]·nH2O (M = FeII, CoII, NiII and x = 0 or 1) obtained under solvothermal conditions exhibit unusual high water solubility making these compounds promising synthons for generation of new POV structure types. Electrospray ionization mass spectrometry provides evidence (i) for a water molecule encapsulated inside the cavity of a fraction of the spherical cluster shells, (ii) for a post-functionalization in water, namely a slow exchange of VO against Sb2O, (iii) for the inner-phase reactivity of the encapsulated water that is capable of opening an oxo-bridge, and (iv) for a significant acceleration of the 16O/18O exchange reactions of oxygen atoms in the cluster periphery with surrounding H218O, when encapsulated water is present. To the best of our knowledge, this is the first example in polyoxovanadate chemistry for the transduction of inner-phase reactivity of an encapsulated guest molecule into changes in the outer-phase reactivity of the cluster. Magnetic susceptibility measurements reflect the individual contributions of the frustrated {V15} spin polytope and the {M(en)3}2+ complexes, with very weak coupling between these groups.

Gas-phase reactions of cationic vanadium-phosphorus oxide clusters with C2H(x) (x=4, 6): a DFT-based analysis of reactivity patterns

The reactivities of the adamantane-like heteronuclear vanadium-phosphorus oxygen cluster ions [V(x)P(4-x)O(10)](.+) (x=0, 2-4) towards hydrocarbons strongly depend on the V/P ratio of the clusters. Possible mechanisms for the gas-phase reactions of these heteronuclear cations with ethene and ethane have been elucidated by means of DFT-based calculations; homolytic C-H bond activation constitutes the initial step, and for all systems the P-O(.) unit of the clusters serves as the reactive site. More complex oxidation processes, such as oxygen-atom transfer to, or oxidative dehydrogenation of the hydrocarbons require the presence of a vanadium atom to provide the electronic prerequisites which are necessary to bring about the 2e(-) reduction of the cationic clusters.

Methane activation by V3PO10(˙+) and V4O10(˙+) clusters: a comparative study

A series of vanadium and phosphorus heteronuclear oxide cluster cations (V(x)P(y)O(z)(+)) are prepared by laser ablation and the reactions of V(3)PO(10)˙(+) and V(4)O(10)˙(+) with methane in a fast flow reactor under the same conditions are studied. A time of flight mass spectrometer is used to detect the cluster distribution before and after reactions. In addition to previously identified reaction of V(4)O(10)˙(+) + CH(4)→ V(4)O(10)H(+) + CH(3)˙, the observation of hydrogen atom pickup cluster V(3)PO(10)H(+) suggests the reaction: V(3)PO(10)˙(+) + CH(4)→ V(3)PO(10)H(+) + CH(3)˙. The rate of the reaction of V(4)O(10)˙(+) with CH(4) is approximately 2.5 times faster than that of V(3)PO(10)˙(+) with CH(4). Density functional theory (DFT) calculations predict that structure of V(3)PO(10)˙(+) is topologically similar to that of V(4)O(10)˙(+), as well as that of P(4)O(10)˙(+), which is very similar to V(4)O(10)˙(+) in terms of methane activation in previous studies. The facile methane activation by the homo- and hetero-nuclear oxide clusters can all be attributed to the presence of an oxygen-centered radical (O˙) in these clusters. Further theoretical study indicates that the O˙ radical (or spin density of the cluster) can transfer within the high symmetry V(4)O(10)˙(+) and P(4)O(10)˙(+) clusters quite easily, and CH(4) molecule further enhances the rate of intra-cluster spin density transfer. In contrast, the intra-cluster spin density transfer within low symmetry V(3)PO(10)˙(+) is thermodynamically forbidden. The experimentally observed reactivity difference is consistent with the theoretical consideration of the intra-cluster spin density transfer.