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Understanding the properties of small particles working under high-temperature conditions at the atomistic scale is imperative for exact control of related processes, but it is quite challenging to achieve experimentally. Herein, benefitting from state-of-the-art mass spectrometry and by using our newly designed high-temperature reactor, the activity of atomically precise particles of negatively charged vanadium oxide clusters toward hydrogen atom abstraction (HAA) from methane, the most stable alkane molecule, has been measured at elevated temperatures up to 873 K. We discovered the positive correlation between the reaction rate and cluster size that larger clusters possessing greater vibrational degrees of freedom can carry more vibrational energies to enhance the HAA reactivity at high temperature, in contrast with the electronic and geometric issues that control the activity at room temperature. This finding opens up a new dimension, vibrational degrees of freedom, for the simulation or design of particle reactions under high-temperature conditions. [ABSTRACT FROM AUTHOR]

Atomic oxygen radical anion (O⋅−) represents an important type of reactive centre that exists in both chemical and biological systems. Gas‐phase atomic clusters can be studied under isolated and well controlled conditions. Studies of O⋅−‐containing clusters in the gas‐phase provide a unique strategy to interpret the chemistry of O⋅− radicals at a strictly molecular level. This review summarizes the research progresses made since 2013 for the reactivity of O⋅− radicals in the atomically precise metal oxide clusters including negatively charged, nanosized, and neutral heteronuclear metal clusters benefitting from the development of advanced experimental techniques. New electronic and geometric factors to control the reactivity and product selectivity of O⋅− radicals under dark and photo‐irradiation conditions have been revealed. The detailed mechanisms of O⋅− generation have been discussed for the reaction systems of nanosized and heteroatom‐doped metal oxide clusters. The catalytic reactions mediated by the O⋅− radicals in metal clusters have also been successfully established and the microscopic mechanisms about the dynamic generation and depletion of O⋅− radicals have been clearly understood. The studies of O⋅− containing metal oxide clusters in the gas‐phase provided new insights into the chemistry of reactive oxygen species in related condensed‐phase systems. [ABSTRACT FROM AUTHOR]

The reactivity of vanadium oxide cluster anions (V2O5)NO− (N = 1–18) that feature with vanadium oxyl radicals (V–O⋅−) toward the most stable alkane, methane, at 273 K has been characterized by employing a newly home-made ship-lock type reactor coupled with a time-of-flight mass spectrometer. The rate constants were determined in the orders of magnitude of 10−16–10−18 cm3 molecule−1 s−1, which significantly breaks the detection limit of predecessors that the reactivity of metal-oxyl radicals (Mn+–O⋅−) with rate constants higher than 10−14 cm3 molecule−1 s−1 could usually be measured. The dynamic structural rearrangement of the cluster skeleton has been proposed to account for the size-dependent reactivity of (V2O5)1–5O− clusters, which may also function in tuning the reactivity of large-sized (V2O5)6–18O− clusters. This work provides new insights into the mechanism of Mn+–O⋅−-mediated C–H activation of methane at a strictly molecular level and expands the activity landscape of Mn+–O⋅− radicals. [ABSTRACT FROM AUTHOR]

A high-temperature linear ion trap that can stably run up to 873 K was newly designed and installed into a homemade reflectron time-of-flight mass spectrometer coupled with a laser ablation cluster source and a quadrupole mass filter. The instrument was used to study the pyrolysis behavior of mass-selected (V2O5)NO− (N = 1–6) cluster anions and the dissociation channels were clarified with atomistic precision. Similar to the dissociation behavior of the heated metal oxide cluster cations reported in literature, the desorption of either atomic oxygen atom or molecular O2 prevailed for the (V2O5)NO− clusters with N = 2–5 at 873 K. However, novel dissociation channels involving fragmentation of (V2O5)NO− to small-sized VxOy− anions concurrent with the release of neutral vanadium oxide species were identified for the clusters with N = 3–6. Significant variations in branching ratios for different dissociation channels were observed as a function of cluster size. Kinetic studies indicated that the dissociation rates of (V2O5)NO− monotonically increased with the increase in cluster size. The internal energies carried by the (V2O5)NO− clusters at 873 K as well as the energetics data for dissociation channels have been theoretically calculated to rationalize the experimental observations. The decomposition behavior of vanadium oxide clusters from this study can provide new insights into the pyrolysis mechanism of metal oxide nanoparticles that are widely used in high temperature catalysis. [ABSTRACT FROM AUTHOR]

Cost-effective and readily accessible 3d transition metals (TMs) have been considered as promising candidates for alkane activation while 3d TMs especially the early TMs are usually not very reactive with light alkanes. In this study, the reactivity of Vn+ and VnO+ (n = 1–9) cluster cations towards ethane under thermal collision conditions has been investigated using mass spectrometry and density functional theory calculations. Among Vn+ (n = 1–9) clusters, only V3–5+ can react with C2H6 to generate dehydrogenation products and the reaction rate constants are below 10−13 cm3 molecule−1 s−1. In contrast, the reaction rate constants for all VnO+ (n = 1–9) with C2H6 significantly increase by about 2–4 orders of magnitude. Theoretical analysis evidences that the addition of ligand O affects the charge distribution of the metal centers, resulting in a significant increase in the cluster reactivity. The analysis of frontier orbitals indicates that the agostic interaction determines the size-dependent reactivity of VnO+ cluster cations. This study provides a novel approach for improving the reactivity of early 3d TMs. [ABSTRACT FROM AUTHOR]

Due to the extraordinary catalytic activity in redox reactions, the noble metal, rhodium, has substantial industrial and laboratory applications in the production of value-added chemicals, synthesis of biomedicine, removal of automotive exhaust gas, and so on. The main drawback of rhodium catalysts is its high-cost, so it is of great importance to maximize the atomic efficiency of the precious metal by recognizing the structure–activity relationship of catalytically active sites and clarifying the root cause of the exceptional performance. This Perspective concerns the significant progress on the fundamental understanding of rhodium chemistry at a strictly molecular level by the joint experimental and computational study of the reactivity of isolated Rh-based gas phase clusters that can serve as ideal models for the active sites of condensed-phase catalysts. The substrates cover the important organic and inorganic molecules including CH4, CO, NO, N2, and H2. The electronic origin for the reactivity evolution of bare Rhxq clusters as a function of size is revealed. The doping effect and support effect as well as the synergistic effect among heteroatoms on the reactivity and product selectivity of Rh-containing species are discussed. The ingenious employment of diverse experimental techniques to assist the Rh1- and Rh2-doped clusters in catalyzing the challenging endothermic reactions is also emphasized. It turns out that the chemical behavior of Rh identified from the gas phase cluster study parallels the performance of condensed-phase rhodium catalysts. The mechanistic aspects derived from Rh-based cluster systems may provide new clues for the design of better performing rhodium catalysts including the single Rh atom catalysts. [ABSTRACT FROM AUTHOR]

The reactivity of chromium oxide cluster anions (CrO3)1−4O− towards low carbon (C1−C4) alkanes has been experimentally investigated at 298 K by employing a homemade ship-lock-type reactor coupled with a time-of-flight mass spectrometer. The results demonstrate that while CrO4− and Cr2O7− clusters could abstract a hydrogen atom from C2H6 and CH4, respectively, Cr3O10− and Cr4O13− clusters were found to be inert towards n-C4H10 within the detection limit. Theoretical results reveal that CrO4− and Cr2O7− clusters possess delocalized chromium-bonded oxygen radicals (Cr−O−·), which rationalizes the hydrogen atom abstraction reactions between (CrO3)1,2O− clusters and alkanes. However, the active sites of (CrO3)3,4O− clusters evolve to peroxide species (O22−), which exhibit inferior activity compared to O−· radicals. The increase of Cr-3d orbital energy driven by the more negative charge around CrOy unit formed via downsizing the cluster size has been proposed to account for favorable reduction of O22− and selective generation of reactive O−· radicals in small-sized (CrO3)1,2O− clusters. This study not only enriches the chemistry of metal-bonded O−· radicals toward alkane activation under mild conditions, but also provides a new insight into the conversion between O22− and O−· radicals over metal oxides. [ABSTRACT FROM AUTHOR]

Methane is an abundant and cheap feedstock to produce valuable chemicals. The catalytic reaction of methane conversion generally requires the participation of multiple molecules (such as two or three CH4 molecules, O2, CO2, etc.). Such complex process includes the cleavage of original chemical bonds, formation of new chemical bonds, and desorption of products. The gas phase study provides a unique arena to gain molecular‐level insights into the detailed mechanisms of bond‐breaking and bond‐forming involved in complicated catalytic reactions. In this Review, we introduce the methane conversion catalyzed by gas phase ions containing metals and three topics will be discussed: (1) the direct coupling of methane molecules, (2) the conversion of CH4 with O2, O3 and N2O, and (3) the conversion of CH4 with CO2 and H2O. The obtained mechanistic aspects may provide new clues for rational design of better‐performing catalysts for conversion of methane to value‐added products. [ABSTRACT FROM AUTHOR]

In the title compound, [Cu(SO4)(C15H11N5)(H2O)]·CH3OH·2H2O, the CuII ion is in a distorted square-pyramidal geometry, in which three N atoms from the chelating 1-(1,10-phenanthrolin-2-yl)-1H-pyrazol-3-amine ligand and one O atom from a sulfate anion define the basal plane and the O atom from the coordinating water molecule is located at the apex. In the crystal, hydrogen-bonding interactions involving the coordinating and solvent water molecules, the methanol solvent molecule and the amine group (one with an intramolecular interaction to one of the sulfate O atoms) of the complex are observed. π–π interactions between symmetry-related phenantroline moieties, with a shortest centroid–centroid interaction of 3.573 (2)°, are also present.