Ionization and Dissociation of Benzene and Aniline under Deep Ultraviolet Laser Irradiation

We report a study on photo-ionization of benzene and aniline with incidental subsequent dissociation by the customized reflection time-of-flight mass spectrometer utilizing a deep ultraviolet 177.3 nm laser.Highly efficient ionization of benzene is observed with a weak C4H3+fragment formed by undergoing disproportional C-C bond dissociation.In comparison,a major C5H6+·fragment and a minor C6H6+·radical are produced in the ionization of aniline pertaining to the removal of CNH·and NH·radicals,respectively.First-principles calculation is employed to reveal the photo-dissociation pathways of these two molecules having a structural difference of just an amino group.It is demonstrated that hydrogen atom transfer plays an important role in the cleavage of C-C or C-N bonds in benzene and aniline ions.This study is helpful to understand the underlying mechanisms of chemical bond fracture of benzene ring and related aromatic molecules.

How ligand coordination and superatomic-states accommodate the structure and property of a metal cluster:Cu_(4)(dppy)_(4)Cl_(2)vs.Cu_(21)(dppy)_(10)with altered photoluminescence

We have synthesized two copper nanoclusters(NCs)with a protection of the same ligand diphenylphosphino-2-pyridine(C_(17)H_(14)NP,dppy for short),formulated as Cu_(4)(dppy)_(4)Cl_(2)and Cu21(dppy)10,respectively.The former one bears a distorted tetrahedron Cu4 core with its six edges fully protected by chlorine and dppy ligands,while the latter presents a symmetric Cu_(21)core on which ten dppy molecules function as monolayer protection via well-organized monodentate or bidentate coordination.Interestingly,the Cu_(4)(dppy)_(4)Cl_(2)cluster exhibits a strong yellow emission at∼577 nm,while Cu_(21)(dppy)_(10)displays dual emissions in purple(∼368 nm)and green(∼516 nm)regions respectively.In combination with TD-DFT calculations,we demonstrate the origin of altered emissions and unique stability of the two copper nanoclusters pertaining to the ligand coordination and metallic superatomic states.

Plasma-Assisted Dinitrogen Activation via Dual Platinum Cluster Catalysis:A Strategy for Ammonia Synthesis under Mild Conditions

The activation and reduction of N_(2)to produce ammonia under mild conditions is of great interest,but challenges remain.Here,we report a breakthrough in efficient dinitrogen cleavage by employing small Ptn+(n=1–4)clusters and convenient plasma assistance.The reactivity of Pt3+is found to be substantially higher than that of other clusters,and the formed Pt3N7+shows prominent mass abundance among the odd-nitrogen products.We illustrate that a chain reaction path within dual cluster cooperation,especially via a“3+2”mode,is beneficial to N≡N triple bond dissociation,embodying efficient synergistic catalysis.A key intermediate containing a bridged N_(2)of binding with two Pt clusters facilitates N_(2)activation with significantly enhanced interactions between the d orbitals of Pt and the antibondingπ*-orbitals of N_(2).Furthermore,by reacting the Pt_(n)N_(m)+clusters with H_(2),we observed hydrogenation products of both evenand odd-hydrogen species,indicative of ammonia release.The in situ synthesized platinum nitride clusters,typically Pt_(3)N_(7)+,induce a highly active N site for hydrogen anchoring,enabling a cost-effective hydrotreating process for ammonia synthesis.

Nitrogen reduction reaction on small iron clusters supported by N-doped graphene:A theoretical study of the atomically precise active-site mechanism

Nonprecious metal catalysts are known of significance for electrochemical N2 reduction reaction(NRR)of which the mechanism has been illustrated by ongoing investigations of single atom catalysis.However,it remains challenging to fully understand the size-dependent synergistic effect of active sites inherited in substantial nanocatalysts.In this work,four types of small iron clusters Fen(n=1–4)supported on nitrogen-doped graphene sheets are constructed to figure out the size dependence and synergistic effect of active sites for NRR catalytic activities.It is revealed that Fe3 and Fe4 clusters on N4G supports exhibit higher NRR activity than single-iron atom and iron dimer clusters,showing lowered limiting potential and restricted hydrogen evolution reaction(HER)which is a competitive reaction channel.In particular,the Fe4-N4G displays outstanding NRR performance for“side-on”adsorption of N2 with a small limiting potential(−0.45 V).Besides the specific structure and strong interface interaction within the Fe4-N4G itself,the high NRR activity is associated with the unique bonding/antibonding orbital interactions of N-N and N-Fe for the adsorptive N2 and NNH intermediates,as well as relatively large charge transfer between N2 and the cluster Fe4-N4G.

Nitrogen-carbon layer coated nickel nanoparticles for efficient electrocatalytic reduction of carbon dioxide

The application of nickel in electrocatalytic reduction of CO2 has been largely restricted by side reaction (hydrogen evolution reaction) and catalyst poisoning.Here we report a new strategy to improve the electrocatalytic performance of nickel for CO2 reduction by employing a nitrogen-carbon layer for nickel nanoparticles.Such a nickel electrocatalyst exhibits high Faradaic efficiency 97.5% at relatively low potential of-0.61 V for the conversion of CO2 to CO.Density functional theory calculation reveals that it is thermodynamically accomplishable for the reduction product CO to be removed from the catalyst surface,thus avoiding catalyst poisoning.Also,the catalyst renders hydrogen evolution reaction to be suppressed and hence reasonably improves catalytic performance.

Chlorine-passivated superatom Al37clusters for nonlinear optics

Utilizing a facile top-down synthetic procedure, here we report the finding of a chlorine-passivated Al_(37) superatom cluster. It is demonstrated that the presence of electrophilic groups, severing as protecting ligands, alters the valence electron count of the metallic core and stabilize the as-prepared aluminum clusters especially when even-numbered chlorine atoms are located at equilibrium positions. Following the discussion regarding their reasonable stabilities, we illustrate the feasible reaction pathways in forming such chlorine-passivated Al_(37) superatom clusters which bear delocalized superatomic orbitals with five valence 3P^5 electrons shifting to the chlorine ligands indicative of a closed electron shell 2F^(14) of the metal core. The successful synthesis of such chlorine-protected aluminum clusters evidences the compatibility of general theory of cluster chemistry in both gas phase and wet chemistry. Such simple-ligand-protected aluminum clusters exhibit reverse-saturated-absorption(RSA) nonlinear optical property pertaining to electronic transitions within the discrete energy states of cluster materials.

In-situ generation and global property profiling of metal nanoclusters by ultraviolet laser dissociation-mass spectrometry

Metal nanoclusters are promising nanomaterials with unique properties, but only a few ones with specific numbers of metal atoms can be obtained and studied up to now. In this study, we establish a new paradigm of in-situ generation and global study of metal nanoclusters with different sizes, constitutions, and charge states, including both accurate constitution characterization and global activity profiling. The complex mixtures of metal nanoclusters are produced by employing single-pulsed 193-nm laser dissociation of monolayer-protected cluster(MPC) precursors within a high-resolution mass spectrometry(HRMS). More than400 types of bare gold nanoclusters including novel multiply charged(2+ and 3+), S-/P-doped, and silver alloy ones can be efficiently generated and accurately characterized. A distinct size(1 to 142 atoms)-and charge(1+ to 3+)-hierarchy reactivity is clearly observed for the first time. This global cluster study might greatly promote the developments and applications of novel metal nanoclusters.

A facile method to synthesize water-soluble Pd8 nanoclusters unraveling the catalytic mechanism of p-nitrophenol to p-aminophenol

Hydroge nation of p-n itrophe nol(PNP)towards the con versi on to p-ami nophe no I(PAP)by metal catalysis is known as a simple and I eco-frie ndly tech nique for the production of corresp on ding in dustrial and pharmaceutical in termediates.While continu ous efforts are paid for§more sustainable and greener procedures by using transition metal catalysts,atomic-precise reaction mechanism for the PNP-to-PAP is still illusive to be fully un derstood.Utilizi ng a dry-wet com bined strategy,here we have syn thesized water-soluble Pd8 nano clusters(NCs)with mercaptosuccinic acid(H2SMA)as the ligand,and the Pd8 NCs found high catalytic performance for the conversion of PNP-to-PAP,as identified by the electrospray ionization mass spectrometer(ESI-MS)measurement.The gradual changes over time of ultraviolet-visible(UV-vis)spectra of PNP really display the catalytic reduction by NaBH4 in presence of Pd8 NCs.Further,in-depth charge transfer interactions between PNP and the Pd8 clusters at the proton-rich conditions are investigated by natural bond orbital(NBO)analysis and electron density differenee(EDD)analysis.The exothermic and kinetic-favorable reaction pathways are addressed,based on successive PNP hydrogenation and H2O removal processes,clarifying the reaction mechanism of Pd catalysts.It is worth noting that this solid-state synthetic route for such Pd8 clusters enables gram-scale quantity of production in likely practical use.

Small gold clusters catalyzing oxidant-free dehydrogenation of glycerol initiated by methene hydrogen atom transfer

Developing oxygen-free methodology for the conversion of alcohols to carbonyls is essentially important because it suppresses the over-oxidation of alcohols to carboxylic acids and enables the production of energetic hydrogen.Here we report a finding of feasible oxidant-free dehydrogenation of glycerol over chemically-pure Au clusters synthesized by a green chemistry method named as laser ablation in liquid(LAL).As results,glycerol is dehydrogenated to form glyceraldehyde which undergoes subsequent dehydrogenation to hydroxymethyl glyoxal.For this,reaction dynamics calculations find interesting dehydrogenation reaction pathways with a low-energy barrier of transition state initiated by hydrogen atom transfer from methene,which differs from the general reaction mechanism based on hydroxyl.Furthermore,it is interesting that the presence of additionalààOH group molecules especially H2O can effectively lower the energy barrier in the activation of the OààH and CààH bonds in glycerol.This principle is also applicable to the oxidant-free dehydrogenation of methanol and ethanol,helping to fully understand the catalytic mechanism of alcohols conversion chemistry.

The reactivity of O_(2) with copper cluster anions Cu_(n)^(-)(n = 7-20):Leveling effect of spin accommodation

The activation of molecular oxygen is an important step in metal-catalyzed oxidation reactions and a hot subject for the research of gas-phase metal clusters.It is known that the Ag and Au clusters readily re-act with O_(2)when they have open shell electronic structures.Distinct from this,here we observed Cu_(n)^(-)(n=7−20)clusters of both open and closed shells possess high reactivity with O_(2)with few exceptions.In a combination with ab initio calculations,we demonstrate that the activation of O_(2)on the even-and odd-sized Cu_(n)^(-)clusters follows the single and double electron transfer models,respectively.Such phe-nomenon of metal clusters with different basicity to activate oxygen is enabled by the leveling effect of spin accommodation.The activity of Cu_(n)^(-)clusters is correlated to the HOMO level,and for the close-shell clusters is also governed by the vertical spin excitation energy(VSE).In encountering the attack of dioxygen,the activity of the copper cluster anions not only depends on their basicity to donate electrons,but also closely associated with the cluster sizes.Small copper clusters Cu_(n)^(-)(n=7−13)can dissociate O_(2)spontaneously,while large clusters require extra energies and display close relationship between the reaction rates and electronic vertical detachment energies(VDE).Our work illuminates a novel reaction mechanism between Cu_(n)^(-)clusters and O_(2),which sheds light in manipulating the activity and stability of coinage clusters by controlling the spin and charge states.

Spectroscopic identification towards tunable mesoscale aggregates of zinc tetraphenylporphyrin for materials

We present a study of spectroscopic identification towards the molecular aggregates of zinc tetraphenylporphyrin （ZnTPP） illustrating how the energy states and intermolecular interactions determine the tunable properties of functional materials in condensation processes. Distinguishable fingerprints of ZnTPP nanorods and nanosheets are addressed utilizing X-ray diffraction （XRD）, Raman and UV-vis absorption spectroscopies. Although these ZnTPPs are assigned to J-aggregation at different extent, the spectral analysis reveals a significant role of the intermolecular interactions associated with varying mesoscale architectures. Energy decomposition analysis （EDA） revealed that the varied ZnTPP aggregates are stabilized by altered dispersion interactions due to the dominant ~r...zr stacking between the monomers.

Superatomic Signature and Reactivity of Silver Clusters with Oxygen:Double Magic Ag_(17)^– with Geometric and Electronic Shell Closure

Understanding the stability and reactivity of silver clusters toward oxygen provides insights to design new materials of coinage metals with atomic precision.Herein,we report a systematic study on anionic silver clusters,Ag_(n)^(−)(n=10-34),by reacting them with O_(2) under multiple-collision conditions.Mass spectrometry observation presents the odd-even alternation effect on the reaction rates of these Agn−clusters.

Co_(12)C^(-)_(12)--metallo-carbospherenes:a new class of magic clusters for hydrogen storage

Metal carbides play significant roles in electronics and materials science due to their unique properties,high strength,and high melting points.Also,they are applied in various organometallic synthesis and catalytic reactions,such as in the Fischer-Tropsch process and olefin metathesis[1,2],and they are able to adsorb small gas molecules such as hydrogen showing promising application for the hydrogen storage[3].Hydrogen is known as a sustainable solution for rising energy demands and an environmentally friendly option to replace fossil fuels.Enormous efforts have been made to develop hydrogen storage materials[4],with the aim to facilitate the application of hydrogen energy for achieving the future carbon–neutral goal set by governments.It has been recognized that the removal of the metal-bound terminal ligands and the doping of transition metals(TMs)on carbon substrates can improve the capacity of hydrogen adsorption[5,6].

Unraveling weak interactions in aniline-pyrrole dimer clusters

Weak intermolecular interactions in aniline-pyrrole dimer clusters have been studied by the dispersion-corrected density functional theory(DFT) calculations. Two distinct types of hydrogen bonds are demonstrated with optimized geometric structures and largest interaction energy moduli. Comprehensive spectroscopic analysis is also addressed revealing the orientation-dependent interactions by noting the altered red-shifts of the infrared and Raman activities. Then we employ natural bond orbital(NBO)analysis and atom in molecules(AIM) theory to have determined the origin and relative energetic contributions of the weak interactions in these systems. NBO and AIM calculations confirm the V-shaped dimer cluster is dominated by N.H···N and C.H···π hydrogen bonds, while the J-aggregated isomer is stabilized by N.H···π, n→π* and weak π···π* stacking interactions.The noncovalent interactions are also demonstrated via energy decomposition analysis associated with electrostatic and dispersion contributions.

Ligand accommodation causes altered reactivity of silver clusters with iodomethane:superatomic stability of Ag_(9)I_(2)^(+)in mimicking XeF_(2)

Exploring metal cluster reactivity with alkyl halides enables to understand the related chemical mechanism of metal surfaces in terms of active sites.Here we report a study of Ag_(n)^(+)(n=1-27)clusters reacting with iodomethane by a flow tube apparatus in tandem with a customized triple quadrupole mass spectrometer.Strong even/odd alternation of the Ag_(n)^(+)is observed in their reactions with CH_(3)I,where silver clusters with even-number,Ag_(2n)^(+),find favorable products of Ag_(2n)I_(1,3)^(+)series,while the Ag_(2n−1)^(+)clusters form Ag_(2n−1)I_(2,4)^(+)products.Interestingly,Ag_(9)^(+)shows up with prominent mass abundance but allows for the formation of Ag_(9)I_(2)^(+),which finds an echo with the formation of Ag_(10)I_(3)^(+).We illustrate the enhanced stability of Ag_(9)I_(2)^(+)and Ag_(10)I_(3)^(+)by showing their significantly enlarged highest occupied molecular orbital(HOMO)-lowest unoccupied molecular orbital(LUMO)gaps and balanced charge distribution compared with the bare metal clusters,respectively.Also elucidated,is the superatomic nature of these bare and iodinated silver clusters,especially Ag_(9)I_(2)^(+)which mimics the rare-gas compound XeF_(2).This study expands a vivid example of special and general superatoms,and enriches the general knowledge on how a ligand stabilizes a metal cluster.

Spin accommodation and reactivity of nickel clusters with oxygen:Aromatic and magnetic metalloxocube Ni_(13)O_(8)^(±)

Due to challenges in preparing pure metal clusters and in controlling reactions,the oxides produced by metal clusters reacting with oxygen are often different from traditional ion-molecule products in the gas phase and their reactivity pattern is also largely unveiled yet.In this work,utilizing a customized Re-TOFMS having a home-made cluster source and a flow tube reactor,we have observed the gaseous reactions of Nin±clusters with oxygen and found magic clusters of Ni_(13)O_(8)±that dominate the mass distributions.By quantum chemistry calculations,we find that both Ni_(13)O_(8)−and Ni_(13)O_(8)+clusters bear a regular cubic structure with 8 oxygen anchoring the eight angles,however,they have rather different spin accommodations.The Ni_(13)O_(8)−clusters have 15 unpaired spin-up electrons exhibiting cubic aromaticity and decent ferromagnetism,while the Ni_(13)O_(8)+clusters take a lower-spin ground state(11 unpaired electrons),with spin-down population on the central Ni atom pertaining to ferrimagnetism.This is a class of metalloxocube clusters that hold properties of aromaticity and ferromagnetism/ferrimagnetism charcterized by a few spin electrons,which embodies the bonding nature of superatomic compounds and enables to develop cluster-genetic materials of multi-functionality.

A comparative study on the reactivity of cationic niobium clusters with nitrogen and oxygen

We have prepared well-resolved Nb^(+)_(n)(n=1-10)clusters and report here an in-depth study on the es-sentially different reactivity with N_(2)and O_(2),by utilizing a multiple-ion laminar flow tube reactor in tandem with a customized triple quadrupole mass spectrometer(MIFT-TQMS).As results,the Nb^(+)_(n)clus-ters are found to readily react with N_(2)and form adsorption products Nb_(n)N^(+)_(2m);in contrast,the reactions with O_(2)give rise to Nb_(n)O^(+)_(1−4)products,and the odd-oxygen products indicate O-O bond dissociation,as well as increased mass abundance of NbO^(+)pertaining to oxygen-etching reactions.We illustrate how N_(2) prefers a physical adsorption on Nb^(+)_(n)clusters with an end-on orientation for all the products,and allow for size-selective Nb^(+)_(n)clusters to act as electron donor or acceptor in forming Nb_(n)N^(+)_(2m).In contrast to these nitrides,the dioxides Nb_(n)O+2display much larger binding energies,with O_(2)always as an electron acceptor,corresponding to superoxide or peroxide states in the initial reactions.Density-of-states and orbital anal-yses show that the interactions between Nb^(+)_(n)and O_(2)are dominated by strongπ-backdonation indicative of incidental electron transfer;whereas weakπ-backdonation and simultaneousσdonation interactions exist in Nb_(n)N^(+)_(2).Further,reaction dynamics analysis illustrates the different interactions for N_(2)and O_(2) in approaching the Nb^(+)_(n)clusters,showing the energy diagrams for N_(2)adsorption and O-O bond dissoci-ation in producing odd-oxygen products.Fragment analyses with orbital correlation and donor-acceptor charge transfer are also performed,giving rise to full insights into the reactivities and interactions of such transition metal clusters with typical diatomic molecules.

Pure Metal Clusters with Atomic Precision for Nanomanufacturing

Advances in cluster science have enabled the preparation of atomically precise metal clusters with one to a hundred atoms under controllable expansion conditions.After introducing typical gas-phase cluster preparation and reaction apparatuses,this work summarized recent progress in preparing pure metal clusters of single-atom resolution,including neutral and ionic ones,with typical examples of Al,V,Nb,Fe,Co,Ni,Rh,Pt,Ag,Cu,and Pb.With the development of soft-landing deposition technology,the size-selective pure metal clusters with strict atomic precision and predictive property will benefit nanomanufacturing down to atomic and near-atomic scales.This work serves as a modest motivation to stimulate the interest of scientists focusing on interdisciplinary subjects.

Enhanced Catalysis of Pt_(3) Clusters Supported on Graphene for N–H Bond Dissociation

We report an in-depth study of catalytic N–H bond dissociation with typical platinum clusters on gra-phene supports.Among all the pristine graphene-and defective graphene-supported Pt clusters of different sizes that were studied,the Pt_(3)/G cluster possesses the highest reactivity and lowest activa-tion barriers for each step of N–H dissociation in the decomposition of ammonia.

Formation of Al^(+)(C_(6)H_(6))_(13):The Origin of Magic Number in Metal-Benzene Clusters Determined by the Nature of the Core

The identification of highly abundant,“magic”spe-cies in the mass spectra of clusters have proven to be valuable in nanoscience,leading to the discovery of new stable species such as fullerenes and the elec-tronic shell structures of metallic clusters.