Transition Metal Oxide Clusters Research Articles

Platinum-Nickel Oxide Cluster-Cluster Heterostructure Enabling Fast Hydrogen Evolution for Anion Exchange Membrane Water Electrolyzers.

Carbon black has been extensively employed as the support for noble metal catalysts for electrocatalysis applications. However, the nearly catalytic inertness and weak interaction with metal species of carbon black are two major obstacles that hinder the further improvement of the catalytic performance. Herein, we report a surface functionalization strategy by decorating transition metal oxide clusters on the commercial carbon black to offer specific catalytic activity and enhanced interaction with metal species. In the case of NiOx cluster-decorated carbon black, a strongly coupled cluster-cluster heterostructure consisting of Pt clusters and NiOx clusters (Pt-NiOx/C) is formed and delivers greatly enhanced alkaline hydrogen evolution kinetics. The NiOx clusters can not only accelerate the hydrogen evolution process as the co-catalyst, but also optimize the adsorption of H intermediates on Pt and stabilize the Pt clusters. Notably, the anion exchange membrane water electrolyzer with Pt-NiOx/C as the cathode catalyst (with a loading of only 50 μgPt cm-2) delivers the most competitive electrochemical performance reported to date, requiring only 1.90 V to reach a current density of 2 A cm-2. The results demonstrate the significance of surface functionalization of carbonaceous supports toward the development of advanced electrocatalysts.

Mass spectrometry provides insights into the structures of polyoxovanadate alkoxide clusters substituted with Fe and W heterometals

Atom-by-atom substitution is a promising strategy for tailoring the electronic properties of transition metal oxide clusters. This approach typically generates a mixture of species that are difficult to separate using conventional methods. As a result, the characterization of their structures and electronic properties remains challenging. Herein, we use collision-induced dissociation (CID) to study the fragmentation of well-defined Fe- and W-doped Lindquist polyoxovanadate methoxides synthesized as a mixture of singly and doubly substituted species. Fragmentation reveals that Fe heteroatoms are efficiently retained within the metal oxide core. In contrast, one W atom is incorporated into the primary WO2(OCH3)2 neutral loss from both the singly and doubly substituted W-containing clusters. Collision energy-resolved CID provides insights into the fragmentation pathways, which are compared to those of the homometallic polyoxovanadate methoxide species. The incorporation of Fe into the cluster reduces its stability towards fragmentation, which could be attributed to the increase in the relative stability of Fe-containing fragment ions with four metal atoms in comparison with their homometallic analog. The observed fragmentation is rationalized by assuming that Fe atoms are incorporated within the low valent plane, while one W atom occupies the axial out-of-plane position in the cluster.

Transition metal oxide clusters: advanced electrocatalysts for a sustainable energy future.

The comprehensive utilization of sustainable green energy is essential to face the global energy and environmental crisis. The oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and electrocatalytic urea synthesis (EUS) are the pivotal electrocatalytic processes, necessitating the development of low-cost electrocatalysts with high efficiency. Small-sized transition metal oxide (TMO) clusters have attracted a lot of attention because of their exceptional qualities, such as exhibiting a dense array of low-coordinated metal active sites (e.g. abundant metal cation defects and oxygen vacancy), amorphous structures with high surface energy, high atom utilization efficiency, and cost-effectiveness. Furthermore, the synergistic actions between metal clusters and TM-Nx single atom active sites remarkably boost up the electrocatalytic performances, corroborated by density functional theory (DFT). More efforts in this comprehensive feature article are expected to achieve insights into the fundamental understanding of electrocatalytic reaction mechanisms in our lab and serve as a guide for creating cutting-edge electrocatalysts of transition metal oxide clusters.

Intrinsic vs Reaction-Driven Fluxionality in Transition-Metal Oxide Clusters: What Does Probing the Dynamics of M3O6– (M = Mo and W) Reacting with H2O Teach Us?

Fluxionality is an important concept in cluster science, with far reaching implications in the area of catalysis. The interplay between intrinsic structural fluxionality and reaction-driven fluxionality though is underexplored in the literature and is a topic of contemporary interest in physical chemistry. In this work, we present an easy-to-use computational protocol combining ab initio molecular dynamics simulations with static electronic structure computations to ascertain the role of intrinsic structural fluxionality in the course of fluxionality occurring due to a chemical reaction. The reactions of structurally well-defined M3O6- (M = Mo and W) with water─which were originally used in the literature to illustrate the significance of reaction-driven fluxionality in transition-metal oxide (TMO) clusters, were chosen for this study. Besides probing the nature of fluxionality, this work provides the timescale for the key proton-hop step in the fluxionality pathway and further attests to the significance of hydrogen bonding in both stabilizing the key intermediates as well as driving forward the reactions of M3O6- (M = Mo and W) with water. The approach presented in this work becomes valuable given that the use of molecular dynamics alone may not help us in accessing some metastable states whose formation involves an appreciable energy barrier. Similarly, merely obtaining a slice of the potential energy surface via static electronic structure calculations will not be helpful in probing the different types of fluxionality. Hence, there is the need for a combined approach to study fluxionality in structurally well-defined TMO clusters. Our protocol may also serve as a starting point in the analysis of much more complicated fluxional chemistry happening on surfaces wherein the recently developed "ensemble of metastable states" approach to catalysis is deemed to be particularly promising.

In Situ Structure of a Mo-Doped Pt-Ni Catalyst during Electrochemical Oxygen Reduction Resolved from Machine Learning-Based Grand Canonical Global Optimization.

Pt-Ni alloy is by far the most active cathode material for oxygen reduction reaction (ORR) in the proton-exchange membrane fuel cell, and the addition of a tiny amount of a third-metal Mo can significantly improve the catalyst durability and activity. Here, by developing machine learning-based grand canonical global optimization, we are able to resolve the in situ structures of this important three-element alloy system under ORR conditions and identify their correlations with the enhanced ORR performance. We disclose the bulk phase diagram of Pt-Ni-Mo alloys and determine the surface structures under the ORR reaction conditions by exploring millions of likely structure candidates. The pristine Pt-Ni-Mo alloy surfaces are shown to undergo significant structure reconstruction under ORR reaction conditions, where a surface-adsorbed MoO4 monomer or Mo2O x dimers cover the Pt-skin surface above 0.9 V vs RHE and protect the surface from Ni leaching. The physical origins are revealed by analyzing the electronic structure of O atoms in MoO4 and on the Pt surface. In viewing the role of high-valence transition metal oxide clusters, we propose a set of quantitative measures for designing better catalysts and predict that six elements in the periodic table, namely, Mo, Tc, Os, Ta, Re, and W, can be good candidates for alloying with PtNi to improve the ORR catalytic performance. We demonstrate that machine learning-based grand canonical global optimization is a powerful and generic tool to reveal the catalyst dynamics behavior in contact with a complex reaction environment.

One‐pot synthesis of POM‐CaO2@ZIF‐8 nanoparticles with self‐supply of H2O2 for electrically enhanced chemodynamic therapy

Chemodynamic therapy (CDT) is a highly effective clinical treatment strategy based on the Fenton or Fenton‐like responses. However, its efficacy has been greatly limited by the complex tumor microenvironment, TME, such as the low levels of H2O2 and the overexpression of the glutathione (GSH). Polyoxometalates (POMs) are compounds that consist of anionic transition metal oxide clusters, such as tungsten (W) and molybdenum (Mo), and notably, these compounds have excellent redox properties in biological systems that can be utilized therapeutically. Therefore, POM‐CaO2@ZIF‐8 nanoparticles (NPs) have been synthesized and used as a mediator to develop an electrically enhanced CDT strategy. It is hoped that the simultaneous modulation of endogenous (the H2O2 generated by CaO2 NPs and GSH depletion by POM) and exogenous (Electric, E) stimulation enhanced Fenton‐like responses will lead to better therapeutic results. Such a treatment strategy has shown excellent tumor cell killing effects in both in vitro and in vivo studies.

Light-guided tumor diagnosis and therapeutics: From nanoclusters to polyoxometalates

Malignant tumors, with the characteristics of easy metastasis and recurrence, are a serious threat to health of mankind. It is urgent to develop promising clinical cancer targeted agents with combination of rapid diagnosis and efficient therapies. Compared with the conventional photosensitizing agents, the recent advances of nanoagents based on transition metal-oxide clusters possess unique structural and electronic properties, greatly improving cancer survival rate, meanwhile, keeping high contrast imaging. This review provides a brief introduction of metal-oxide clusters, including both nanoclusters to molecular clusters, specifically polyoxometalates (POMs). Subsequently, biocompatibility of metal-oxide clusters is emphasized from aspects of endocytosis, macropinocytosis, and phagocytosis. Through the classification of late and early transition metals oxide clusters, recent outcomes of light-guided nanoagents are represented with their intriguing chemical and optical properties in their diagnosing and photochemotherapy performance. It shed light on the summary of next generation multifunctional cancer targeting agents’ developments as well as outlook of materials selection trends and research direction in the future.

Selective Oxidation of Methane to Methanol over Ceria‐Zirconia Supported Mono and Bimetallic Transition Metal Oxide Catalysts

AbstractSeveral ceria‐zirconia supported mono and bi‐metallic transition metal oxide clusters containing Fe, Cu, and Ni are synthesized by dry impregnation. Through XRD, H2‐TPR, NH3‐TPD, pyridine adsorption followed by FTIR spectroscopy and XAS, the well‐dispersed nature of the transition metal oxide clusters is revealed, and the Lewis acidity of the catalysts is assessed. In‐situ FTIR spectroscopy is used to monitor the methane activation on catalyst surfaces. All catalysts activate methane at 250 °C forming methyl, alkyl, and methoxy species on the catalyst surface. By co‐feeding steam and oxygen together with methane, continuous direct oxidation of methane to methanol can be achieved, with the complete oxidation to CO2 as the other reaction path. Methoxy species are found to be a key intermediate for methanol production. Lowering the methane conversion improves the methanol selectivity. By extrapolation, it is estimated that methanol selectivity close to unity can be achieved below a threshold of methane conversion at about 0.002 %. The formation of CuO and NiO mixed metal oxides produces stronger Lewis acid sites and yields higher methanol selectivity.

Reaction of NO2 with Groups IV and VI Transition Metal Oxide Clusters.

The addition of NO2 to Group IV (MO2)n and Group VI (MO3)n (n = 1-3) nanoclusters was studied using both density functional theory (DFT) and coupled cluster theory (CCSD(T)). The structures and overall binding energetics were predicted for Lewis acid-base addition without transfer of spin (a physisorption-type process) and the formation of either cluster-ONO (HONO-like or bidentate bonding) or NO3- formation where for both the spin is transferred to the metal oxide clusters (a chemisorption-type process). Only chemisorption of NO2 is predicted to be thermodynamically allowed at temperatures ≥298 K for Group IV (MO2)n clusters with the formation of surface chemisorbed NO2 being by far the most energetically favorable. The ligand binding energies (LBEs) for physisorption and chemisorption on the TiO2 nanoclusters are consistent with computational studies of the bulk solids. Chemisorption is only predicted to occur for (CrO3)n clusters in the form of a terminal nitrate containing species whereas the larger chemisorbed nitrate structures for (MoO3)n and (WO3)n were found to be metastable and unlikely to form in any appreciable amount at temperatures of 298 K and higher. NO2 is predicted to only be capable of physisorbing to (MoO3)n and (WO3)n at lower temperatures and therefore unlikely to bind NO2 at temperatures ≥298 K. Correlations between the (MO3)nNO2 ligand bond energies and the chemical properties of the parent (MO3)n clusters (Lewis acidity, ionization potentials, excitation energies, and M = O/M-O bond strengths) are described.

Polyoxometalate/Metal-Organic-Framework Hybrid Materials As Electrodes for Electrochemical Capacitors

Tremendous effort has been focused on developing electrochemical capacitors with various applications such as portable electronics, heavy hybrid vehicles, load leveling, and uninterruptible power supplies.Electrochemical capacitors have the advantage of providing high power density which enable faster charge/discharge rates than batteries, as well as long cycle life. Polyoxometalates (POMs) are transition metal oxide clusters, and they possess fast and reversible multi-electron redox reactions.Several POMs have been studied in supercapacitors, such as H3[PMo12O40], H3[PW12O40],H4[SiMo12O40], H4[SiW12O40]. However, most of POMs can be dissolved in aqueous electrolyte. Therefore, some of them were combined with carbon materials or conducting polymers.In this study, we synthesized a vanadium-based POM combined with a metal-organic-framework (MOF) as electrode material in electrochemical capacitors. The electrochemical properties of this V-POM/MOF electrodes are studied by electrochemical measurements such as galvanostatic charge/discharge and cyclic voltammetry. Furthermore, a hybrid energy storage device which combines V-POM/MOF as negative electrode and activated carbon as positive electrode was assembled to demonstrate the potential for electrochemical capacitor applications.

Time-dependent DFT and experimental study on visible light photocatalysis by metal oxides of Ti, V and Zn after complexing with a conjugated polymer

Tuning the photoactive behavior of transition metal oxide (Ti2O4, V2O5, Zn3O3) cluster units by structural modifications with polythiophene.

Reaction of CO2 with Groups 4 and 6 Transition Metal Oxide Clusters.

Density functional theory (DFT) and coupled cluster theory (CCSD(T)) were used to study the addition of CO2 to group 4 (MO2)n and group 6 (MO3)n (n = 1, 2, 3) nanoclusters. The structures and energetics arising from Lewis acid-base addition (physisorption) and formation of CO32- (chemisorption) of CO2 to these clusters were predicted. Physisorption and chemisorption of CO2 are predicted to be thermodynamically allowed for group 4 (MO2)n clusters, with chemisorption being more favored energetically. Correlations of the ligand binding energies (LBEs) for the group 4 clusters are made with the fluoride affinities and M-O and M═O bond strengths of the clusters. The LBEs for chemisorption on the Zr and Ti clusters are consistent with published experimental and computational studies of bulk solids. Physisorption LBEs for the Ti and Zr clusters are more exothermic than the bulk values, as the cluster models allow for better relaxation at the metal sites. Chemisorption is not predicted to occur with group 6 (MO3)n clusters, as the larger chemisorbed structures were all found to be metastable. CO2 is predicted to weakly physisorb to (WO3)n with physisorption correlating with the Lewis acidity of the metal site.

Reaction of SO2 with Group IV and VI transition metal oxide clusters

The addition of SO2 to the Group IV (MO2)n and VI (MO3)n (n = 1, 2, 3) nanoclusters was studied using density functional theory (DFT) and coupled cluster theory (CCSD(T)). Structures and ligand binding energies were predicted for the Lewis acid-base addition (physisorption), or SO32− or SO42− formation (chemisorption) of SO2 to these clusters. Physisorption is predicted to be thermodynamically allowed for the Mo and W clusters at 298K, and for Cr only at lower temperatures. Chemisorption by SO42− formation is thermodynamically allowed only for Cr clusters due to the higher reducibility of the metal center. Correlations were made between the ligand binding energies (LBEs) of the (MO3)nSO2 clusters and the chemical properties of the parent (MO3)n clusters (Lewis acidity, reducibility, and MO and MO bond strengths). Physisorption and chemisorption by SO32− formation is predicted to be thermodynamically possible for Group IV clusters, and SO4−2 formation is predicted not to occur, suggesting that sulfate formation does not proceed by the direct reaction of a pure metal oxide surface and SO2.

Alexander I. Boldyrev

Angewandte Chemie International EditionVolume 56, Issue 26 p. 7348-7348 Author ProfileFree Access Alexander I. Boldyrev First published: 09 February 2017 https://doi.org/10.1002/anie.201700939AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract “My favorite place on earth is Kauai, Hawaii. My favorite author (fiction) is Mikhail Saltykov-Shchedrin ...” This and more about Alexander I. Boldyrev can be found on page 7348. Alexander I. Boldyrev The author presented on this page has recently published his 10th article in Angewandte Chemie in 10 years: “Peculiar All-Metal σ-Aromaticity of the [Au2Sb16]4− Anion in the Solid State”: I. A. Popov, F.-X. Pan, X.-R. You, L.-J. Li, E. Matito, C. Liu, H.-J. Zhai, Z.-M. Sun, A. I. Boldyrev, Angew. Chem. Int. Ed. 2016, 55, 15344; Angew. Chem. 2016, 128, 15570. Date of birth: December 19, 1951 Position: Professor, Department of Chemistry and Biochemistry, Utah State University E-mail: a.i.boldyrev@usu.edu Homepage: http://ion.chem.usu.edu/∼boldyrev/ ORCID: 0000-0002-8277-3669 Education: 1974 Diploma in Chemistry, Novosibirsk State University 1978 PhD with Prof. Oleg P. Charkin, Institute of New Chemical Problems, USSR Academy of Science, Chernogolovka, and Moscow State University 1987 DSc, Institute of Chemical Physics, USSR Academy of Science, and Physico-Chemical Institute, Moscow 1990–1992 Alexander von Humboldt Fellow with Professor Paul von R. Schleyer, Friedrich-Alexander-Universität Erlangen-Nürnberg Awards: 1990 Alexander von Humboldt Fellowship; 2008 Utah Award, American Chemical Society Salt Lake Section; 2009 D. Wynne Thorne Career Research Award, Utah State University Current research interests: Developing chemical bonding models for clusters and novel chemical compounds; multicentered chemical bonding My favorite place on earth is Kauai, Hawaii. My favorite author (fiction) is Mikhail Saltykov-Shchedrin. The most important things I learned from my parents are patience and perseverance. If I could have dinner with three famous scientists from history, they would be Dmitry I. Mendeleev, Erwin Schrödinger, and Gilbert N. Lewis. My worst nightmare is to find that a computer program I use for my research has not been working properly. My biggest motivation is my students. I would have liked to have discovered the Periodic Table. My top three films of all time are Mirror (Andrei Tarkovsky), It's a Mad Mad Mad Mad World (Stanley Kramer), and Amarcord (Federico Fellini). The most significant scientific advance of the last 100 years has been the discovery of nuclear and thermonuclear reactions. The biggest problem that scientists face is that a significant part of the society lost trust in science. My favorite type of research is deciphering chemical bonding in new complicated compounds. If I won the lottery, I would buy a big computer cluster. My 5 top papers: References 1“DVM-Xα calculations on the ionization potentials of [MXk+1]− complex anions and the electron affinities of MXk+1 superhalogens”: G. L. Gutsev, A. I. Boldyrev, Chem. Phys. 1981, 56, 277. (18 years later experimentalists confirmed some of the predictions in this simple model.) 2“Observation of All-Metal Aromatic Molecules”: X. Li, A. E. Kuznetsov, H. F. Zhang, A. I. Boldyrev, L. S. Wang, Science 2001, 291, 859. (The concept of aromaticity was extended into metal clusters.) 3“Developing paradigms of chemical bonding: adaptive natural density partitioning”: D. Yu. Zubarev, A. I. Boldyrev, Phys. Chem. Chem. Phys. 2008, 10, 5207. (A new method was proposed for deciphering multicenter bonding in chemistry.) 4“δ Aromaticity in [Ta3O3]−: H.-J. Zhai, B. B. Averkiev, D. Yu. Zubarev, L. S. Wang, A. I. Boldyrev, Angew. Chem. Int. Ed. 2007, 46, 4277; Angew. Chem. 2007, 119, 4355. (δ aromaticity was observed in a transition metal oxide cluster.) 5“Observation of the Highest Coordination Number in Planar Species: Decacoordinated Ta©B10− and Nb©B10− Anions”: T. R. Galeev, C. Romanescu, W.-L. Li, L. S. Wang, A. I. Boldyrev, Angew. Chem. Int. Ed. 2012, 51, 2101; Angew. Chem. 2012, 124, 2143. (The high symmetry and stability of these species is due to the presence of the double (σ and π) aromaticity.) Volume56, Issue26June 19, 2017Pages 7348-7348 ReferencesRelatedInformation

Polyoxometalate Modified Biomass Carbon Composites for Supercapacitor Electrodes

Polyoxometalates (POMs), nanoscale transition metal-oxide clusters, have emerged as promising building blocks for the fabrication of pseudocapacitive electrodes.[i] These POM clusters undergo fast reversible electron transfer reactions and have multiple stable redox states, ideal characteristics for energy storage applications.[ii] In order to leverage these properties for use in electrochemical capacitor (EC) electrodes, these POM clusters must be immobilized on a stable carbon substrate to create a composite electrode. There is synergy in this combination as the POMs contribute faradaic redox processes, while the carbon provides stability, high conductivity, and electrochemical double layer capacitive (EDLC) contributions. Porous carbon derived from biomass is an excellent potential substrate for these POM-carbon composites owing to its low cost, simple synthesis procedure, and high specific surface area. Here, we will report on our synthesis of porous carbon substrates derived from pine cone biomass via a two-stage carbonization and chemical activation procedure. These pine cone carbon samples are highly porous with specific surface areas over 2500 m2 g-1. In a sulfuric acid electrolyte, the high surface area of these samples results in a double layer capacitance of 265 F g-1. In order to further enhance this already large capacitance, the biomass carbons were modified with Keggin POM clusters, PMo12O40 3- and PW12O40 3- via a single step chemisorption. We have discovered that the intrinsic porosity and surface conditions of the pine cone biomass carbon are particularly well suited to the immobilization of Keggin POMs. Additionally, by adjusting the activation conditions, the carbon porosity can be tuned to further enhance POM chemisorption. The result is biomass carbon hybrids with exceptionally high loading of POM clusters. The redox activity of these immobilized POMs leads to significantly enhanced area and volume specific capacitance compared to the bare carbon substrate (Figure 1). In this talk, we will present the full characterization of the POM-biomass carbon hybrids as well as discuss the activation conditions and resulting substrate porosity necessary for superior POM adsorption. The POM chemistry that results in the optimal pseudocapacitive performance will also be presented and discussed. [i] M. Genovese, K. Lian. Current Opinion in Solid State and Materials Science. 19 (2015) 126-127 [ii] B.B Xu, L. Xu, G.G. Gao, W.H. Guo, S.P. Liu. J. Colloid Interface Sci. 330 (2009) 408 Figure 1

Dehydrogenation of propylene mediated by CeVO4+: An interesting example for the chemistry of binary Ce–V transition-metal oxide cluster cations

Laser-ablation-generated cerium-vanadium oxide cluster cations CeVO4+ were mass-selected by applying a quadrupole mass filter, and reacted with propylene in a linear ion trap reactor at ambient conditions. Time-of-flight mass spectrometry and density functional theory calculations were used to characterize the cluster reactions. The CeVO4+ cluster has a closed-shell electronic structure, and is reactive toward propylene leading to the formation of CeVO3C3H4+/H2O and CeVO4C3H6+. The computed results indicate that this reaction involves the occurrence of spin conversions (singlet→triplet), and a new mechanism of dehydrogenation of alkenes, which is different from the reported ones, was proposed. Compared with another closed-shell cluster V3O7+, possessing the similar mass with CeVO4+, the heteronuclear oxide cluster cations show higher reactivity toward propylene. The computational results are in good agreement with the experimental observations. This work provides insights into nature of active sites and reaction mechanisms in related condensed-phase systems at a molecular level.

Polymer-containing Organo-Polyoxometalate: Towards New Catalytic Object.

Polyoxometalates (POMs) are early transition metal oxide clusters, which form a diverse family of compounds with highly tunable shapes, sizes, charges, etc. Generating hybrid structures is an attractive path to increase the structural diversity of POMs. The present article is a personal account that retraces how we inserted polyoxometallic platforms onto polymeric chains. We focused on two main families of functionalized organo-POMs: the organotin-substituted Dawson polyoxotunstates α1 and α2-[P(2)W(17)O(61)(SnR)](7-) and the Dawson vanadotungstates [P(2)V(3)W(15)O(59){(OCH(2))(2)-C(Et)NHC(=O)R}](5-). Herein we discuss how the connection of POMs to polymers affects the self-assembly of the polymers and the catalytic properties of the polyoxometalates.

Gas-phase reaction of CeVO5(+) cluster ions with C2H4: the reactivity of cluster bonded peroxides.

Cerium-vanadium oxide cluster cations CeVO5(+) were generated by laser ablation, mass-selected using a quadrupole mass filter, thermalized through collisions with helium atoms, and then reacted with ethene molecules in a linear ion trap reactor. The cluster reactions have been characterized by time-of-flight mass spectrometry and density functional theory calculations. The CeVO5(+) cluster has a closed-shell electronic structure and contains a peroxide (O2(2-)) unit. The cluster bonded O2(2-) species is reactive enough to oxidize a C2H4 molecule to generate C2H4O2 that can be an acetic acid molecule. Atomic oxygen radicals (O(-)˙), superoxide radicals (O2(-)˙), and peroxides are the three common reactive oxygen species. The reactivity of cluster bonded O(-)˙ and O2(-)˙ radicals has been widely studied while the O2(2-) species were generally thought to be much less reactive or inert toward small molecules under thermal collision conditions. This work is among the first to report the reactivity of the peroxide unit on transition metal oxide clusters with hydrocarbon molecules, to the best of our knowledge.

Group VB transition metal oxide clusters M4O n −/0 (M = Nb, Ta; n = 8–11): structural evolution and chemical bonding

The structural and electronic properties of two series of Group VB transition metal oxide clusters, M4O − and M4O n (M = Nb, Ta; n = 8–11), are investigated using density functional theory calculations. Generalized Koopmans’ theorem is applied to predict the vertical detachment energies and simulate the photoelectron spectra. Large highest occupied molecular orbital–lowest unoccupied molecular orbital gaps are observed for these two stoichiometric M4O10 clusters and estimated to be 3.98 and 4.38 eV for M = Nb and Ta, respectively. The M4O 10 −/0 (M = Nb, Ta) clusters are polyhedral cage structures with high symmetry (T d for the neutral and D 2d for the anion) in which each metal atom joints three bridging and one terminal O atoms. For the Nb oxide species, Nb4O 8 −/0 and Nb4O 9 −/0 can be viewed as removing two and one terminal O atoms from Nb4O 10 −/0 , respectively. The Ta species follow the same rule to the Nb species, except that the anionic Ta4O8 − is formed by removing one terminal and one bridging O atoms from Ta4O10 −. The Ta4O9 containing a localized Ta3+ site can readily react with O2 to form the Ta4O11 which can also be viewed as replacing a terminal oxygen atom in Ta4O10 by a peroxo O2 unit, whereas the added oxygen atom is found to be a bridging one in the O-rich clusters Nb4O 11 −/0 and the anionic Ta4O11 −. Molecular orbital analyses are performed to analyze the chemical bonding in the tetra-nuclear metal oxide clusters and to elucidate their structural and electronic evolution.

Reactivity of Oxygen Radical Anions Bound to Scandia Nanoparticles in the Gas Phase: CH Bond Activation

The activation of C-H bonds in alkanes is currently a hot research topic in chemistry. The atomic oxygen radical anion (O(-·)) is an important species in C-H activation. The mechanistic details of C-H activation by O(-·) radicals can be well understood by studying the reactions between O(-·) containing transition metal oxide clusters and alkanes. Here the reactivity of scandium oxide cluster anions toward n-butane was studied by using a high-resolution time-of-flight mass spectrometer coupled with a fast flow reactor. Hydrogen atom abstraction (HAA) from n-butane by (Sc2O3)(N)O(-) (N=1-18) clusters was observed. The reactivity of (Sc2O3)(N)O(-) (N=1-18) clusters is significantly sizedependent and the highest reactivity was observed for N=4 (Sc8O13(-)) and 12 (Sc24O37(-)). Larger (Sc2O3)(N)O(-) clusters generally have higher reactivity than the smaller ones. Density functional theory calculations were performed to interpret the reactivity of (Sc2O3)(N)O(-) (N=1-5) clusters, which were found to contain the O(-·) radicals as the active sites. The local charge environment around the O(-·) radicals was demonstrated to control the experimentally observed size-dependent reactivity. This work is among the first to report HAA reactivity of cluster anions with dimensions up to nanosize toward alkane molecules. The anionic O(-·) containing scandium oxide clusters are found to be more reactive than the corresponding cationic ones in the C-H bond activation.