Evaporation of tetramers in Sb4n clusters and conditions for the formation of Sb2n+1 clusters

Antimony clusters are produced by the inert gas condensation technique. They are found to be built from Sb₄ units. The fragmentation by evaporation of Sb₄ units is studied as a function of the excess energy in the cluster. By this way the binding energy of the Sb₄ units in the cluster is found to be about 1.5 eV, well below the binding energy of a Sb atom in the bulk and in Sb₄(?3eV). The evolution of ionization potentials of Sb_4n clusters confirms that their structure is probably non metallic. Finally the possible metastable character of this Sb_4n structure is discussed.     

Density functional study of AgnPd and AgnPdH clusters

Small Ag_nPd (n = 5) clusters and their hydrides Ag_nPdH (n = 5) have been studied by density functional theory calculations. For bare clusters, the structures in which the Pd atom has a maximum number of neighboring Ag atoms tend to be energetically favorable. Hydrogen prefers binding to Ag? Pd bridge site of Ag_nPd clusters except for Ag₅Pd. The binding energy has a strong odd–even oscillation. The electron transfers are from Ag atoms to Pd in bare clusters and are from metal clusters to H in cluster hydrides. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

A density functional theory study on the Ag<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>H (<Emphasis Type="Italic">n</Emphasis> = 1–10) clusters

Density functional GGA-PW91 method with DNP basis set is applied to optimize the geometries of Ag _n H (n = 1–10) clusters. For the lowest energy geometries of Ag _n H (n = 1–10) clusters, the hydrogen atom prefers to occupy the two-fold coordination bridge site except the occupation of single-fold coordination site in AgH cluster. After adsorption of hydrogen atom, most Ag _n structures are slightly perturbed and only the Ag₆ structure in Ag₆H cluster is distorted obviously. The Ag–Ag bond is strengthened and the strength of Ag–H bond exhibits a clear odd–even oscillation like the strength of Au–H bond in Au _n H clusters, indicating that the hydrogen atom is more favorable to be adsorbed by odd-numbered pure silver clusters. The adsorption strength of small silver cluster toward H atom is obviously weaker than that of small gold cluster toward H atom due to the strong scalar relativistic effect in small gold cluster. The pronounced odd–even alternation of the magnetic moments is observed in Ag _n H systems, indicating that the Ag _n H clusters possess tunable magnetic properties by adsorbing hydrogen atom onto odd-numbered or even-numbered small silver cluster.     

Ba5Cl4(H2O)8(VPO5)8: a novel three‐dimensional framework solid

The novel hydrothermally synthesized title compound, pentabarium tetrachloride octahydrate octakis(oxovanadium phosphate), Ba₅Cl₄(H₂O)₈(VPO₅)₈, crystallizes in the orthorhombic space group Cmca with a unit cell containing four formula units. Two Ba²⁺ cations, two Cl⁻ anions and the O atoms of four water molecules are situated on the (100) mirror plane, while the third independent Ba²⁺ cation is on the intersection of the (100) plane and the twofold axis parallel to a. Two phosphate P atoms are on twofold axes, while the remaining independent P atom and both V atoms are in general positions. The structure is characterized by two kinds of layers, namely anionic oxovanadium phosphate (VPO₅), composed of corner‐sharing VO₅ square pyramids and PO₄ tetrahedra, and cationic barium chloride hydrate clusters, Ba₅Cl₄(H₂O)₈, composed of three Ba²⁺ cations linked by bridging chloride anions. The layers are connected by Ba—O bonds to generate a three‐dimensional structure.     

Ba14Cu2In4N7, a new subnitride with isolated nitridocuprate groups and indium clusters

Single crystals of Ba₁₄Cu₂In₄N₇, tetradecabarium dicopper tetraindium heptanitride, were synthesized by slow cooling from 1023 K at 7 MPa of N₂ using an Na flux. The compound crystallizes in the monoclinic space group P2/m with Z = 2, and contains ⁰[CuN₂] nitrido­cuprate units and distorted ⁰[In₄] clusters. One Ba atom, not connected to any N atoms, is surrounded by 12 other Ba atoms in a barium cuboctahedron. The structural formula is expressed as (Ba)Ba₂₇N₆[CuN₂]₄[In₄]₂.     

Density functional study of small neutral and charged silver cluster hydrides

Small neutral, anionic, and cationic silver cluster hydrides AgnH and anionic HAgnH (n=1-7) have been studied using the PW91PW91 density functional method. It was found that the most stable structure of the AgnH complex (neutral or charged) does not always come from that of the lowest energy bare silver cluster plus an attached H atom. Among various possible adsorption sites, the bridge site is energetically preferred for the cationic and most cases of neutral Agn. For anionic Agn, the top site is preferred for smaller Agn within n相似文献   

A ternary complex of aqua(18‐crown‐6)bis(o‐nitrophenolato)barium(II), the triaqua(18‐crown‐6)(o‐nitrophenolato)barium(II) cation and the o‐nitrophenolate anion

In the title compound [systematic name: tri­aqua(1,4,7,10,13,16‐hexaoxa­cyclo­octa­decane‐κ⁶O)(2‐nitro­phenolato‐κO)­barium(II)–aqua(1,4,7,10,13,16‐hexaoxa­cyclo­octa­decane‐κ⁶O)‐ bis(2‐nitro­phenolato‐κ²O,O′)­barium(II)–2‐nitro­phenolate (1/1/1)], [Ba(C₁₂H₂₄O₆)(C₆H₄NO₃)(H₂O)₃][Ba(C₁₂H₂₄O₆)(C₆H₄NO₃)₂(H₂O)](C₆H₄NO₃), the two Ba^II atoms encapsulated by the 18‐crown‐6 rings have different coordinations. Although both Ba^II atoms are coordinated to the six O atoms of the crowns, in the neutral moiety, the Ba^II atom is coordinated to one terminal O atom from a water mol­ecule, two phenolate O atoms and two nitro‐group O atoms, while in the cationic moiety, the Ba^II atom is coordinated to three terminal O atoms from water mol­ecules and one phenolate O atom. Both the crowns are eclipsed and translated along the b direction. In the asymmetric unit, the three components are interconnected by four O—H?O interactions. The packing is stabilized by two intermolecular C—H?O interactions and by one O—H?O interaction.     

Non-covalent Interactions and Charge Transfer between Propene and Neutral Yttrium-Doped and Pure Gold Clusters

The dopant and size-dependent propene adsorption on neutral gold (Au_n) and yttrium-doped gold (Au_n−1Y) clusters in the n=5–15 size range are investigated, combining mass spectrometry and gas phase reactions in a low-pressure collision cell and density functional theory calculations. The adsorption energies, extracted from the experimental data using an RRKM analysis, show a similar size dependence as the quantum chemical results and are in the range of ≈0.6–1.2 eV. Yttrium doping significantly alters the propene adsorption energies for n=5, 12 and 13. Chemical bonding and energy decomposition analysis showed that there is no covalent bond between the cluster and propene, and that charge transfer and other non-covalent interactions are dominant. The natural charges, Wiberg bond indices, and the importance of charge transfer all support an electron donation/back-donation mechanism for the adsorption. Yttrium plays a significant role not only in the propene binding energy, but also in the chemical bonding in the cluster-propene adduct. Propene preferentially binds to yttrium in small clusters (n<10), and to a gold atom at larger sizes. Besides charge transfer, relaxation also plays an important role, illustrating the non-local effect of the yttrium dopant. It is shown that the frontier molecular orbitals of the clusters determine the chemical bonding, in line with the molecular-like electronic structure of metal clusters.     

Bare Clusters Derived from Protein Templates: Au25+, Au38+ and Au102+

A discrete sequence of bare gold clusters of well‐defined nuclearity, namely Au₂₅⁺, Au₃₈⁺ and Au₁₀₂⁺, formed in a process that starts from gold‐bound adducts of the protein lysozyme, were detected in the gas phase. It is proposed that subsequent to laser desorption ionization, gold clusters form in the gas phase, with the protein serving as a confining growth environment that provides an effective reservoir for dissipation of the cluster aggregation and stabilization energy. First‐principles calculations reveal that the growing gold clusters can be electronically stabilized in the protein environment, achieving electronic closed‐shell structures as a result of bonding interactions with the protein. Calculations for a cluster with 38 gold atoms reveal that gold interaction with the protein results in breaking of the disulfide bonds of the cystine units, and that the binding of the cysteine residues to the cluster depletes the number of delocalized electrons in the cluster, resulting in opening of a super‐atom electronic gap. This shell‐closure stabilization mechanism confers enhanced stability to the gold clusters. Once formed as stable magic number aggregates in the protein growth medium, the gold clusters become detached from the protein template and are observed as bare Au_n⁺ (n=25, 38, and 102) clusters.     

Density functional study of the interaction between small Au clusters, Au(n) (n=1-7) and the rutile TiO2 surface. II. Adsorption on a partially reduced surface

We use density functional theory to examine the electronic structure of small Au(n) (n=1-7) clusters, supported on a rutile TiO(2)(110) surface having oxygen vacancies on the surface (a partially reduced surface). Except for the monomer, the binding energy of all Au clusters to the partially reduced surface is larger by approximately 0.25 eV than the binding energy to a stoichiometric surface. The bonding site and the orientation of the cluster are controlled by the shape of the highest occupied molecular orbitals (HOMOs) of the free cluster (free cluster means a gas-phase cluster with the same geometry as the supported one). The bond is strong when the lobes of the HOMOs overlap with those of the high-energy states of the clean oxide surface (i.e., with no gold) that have lobes on the bridging and the in-plane oxygen atoms. In other words, the cluster takes a shape and a location that optimizes the contact of its HOMOs with the oxygen atoms. Fivefold coordinated Ti atoms located at a defect site (5c-Ti(*)) participate in the binding only when a protruding lobe of the singly occupied molecular orbital (for odd n) or the lowest unoccupied molecular orbital (for even n) of the free Au(n) cluster points toward a 5c-Ti(*) atom. The oxygen vacancy influences the binding energy of the clusters (except for Au(1)) only when they are in direct contact with the defect. The desorption energy and the total charge on clusters that are close to, but do not overlap with, the vacancy differ little from the values they have when the cluster is adsorbed on a stoichiometric surface. The behavior of Au(1) is rather remarkable. The atom prefers to bind directly to the vacancy site with a binding energy of 1.81 eV. However, it also makes a strong bond (1.21 eV) with any 5c-Ti atom even if that atom is far from the vacancy site. In contrast, the binding of a Au monomer to the 5c-Ti atom of a surface without vacancies is weak (0.45 eV). The presence of the vacancy activates the 5c-Ti atoms by populating states at the bottom of the conduction band. These states are delocalized and have lobes protruding out of the surface at the location of the 5c-Ti atoms. It is the overlap of these lobes with the highest orbital of the Au atom that is the major reason for the bonding to the 5c-Ti atom, no matter how far the latter is from the vacancy. The energy for breaking an adsorbed cluster into two adsorbed fragments is smaller than the kinetic energy of the mass-selected clusters deposited on the surface in experiments. However, this is not sufficient for breaking the cluster upon impact with the surface, since only a fraction of the available energy will go into the reaction coordinate for breakup.     

Strontium tetrafluoridoborate and barium tetrafluoridoborate

In Sr(BF₄)₂, which is isomorphous with the previously published Ca(BF₄)₂, the metal atom possesses a coordination number of 8 with a square‐antiprismatic environment. Each tetrafluoridoborate anion is bonded to four metal centers. In the barium derivative, the metal center, with symmetry 2/m, is surrounded by 14 F atoms. The B atom and two of the three independent F atoms occupy special positions with symmetry m. Each anion is connected to five Ba atoms. This structure differs significantly from an earlier published structure of Ba(BF₄)₂ [published as Ba₂(BF₄)₄; Lin, Cheng, Chen & Huang (1998). Jiegon Huaxue, 17 , 245]. The radial distribution functions for the present Ba(BF₄)₂ and earlier Ba₂(BF₄)₄ structures differ significantly.     

Theoretical Investigation of Binary and Ternary Metal Clusters derived from [Y10M]n— Zintl Ions

The pseudo element concept is applied to isolated Zintl anions [Y₁₀M]^n—, where M is Ni or Zn, and Y is a third group element, which is replaced by a fourth group element X. The aim of the theoretical study is to identify stable binary metal atom clusters and to test the robustness of the Zintl concept. DFT and RIMP2 methods are employed for this purpose. All low‐energy isomers of [X₁₀M]^m+ show structures known from corresponding Zintl anions. A partial replacement of only six third group elements, however, may lead to different low‐energy topologies. The cohesive energy of the clusters X₁₀Ni (X = Si, Ge, Sn, Pb) is significantly higher than that of the bare X₁₀ species, binding energy of the Ni atom amounts to about 5 eV.     

Dibarium zirconium tetraoxalate trihydrate

A new mixed barium zirconium oxalate, tri­aqua­tetra‐μ‐oxalato‐dibarium(II)­zirconium(IV), Ba₂Zr(C₂O₄)₄·3H₂O or [Ba₂Zr(C₂O₄)₄(H₂O)₃]_n, has been synthesized. The complex is built from eightfold‐coordinated Zr atoms and eleven‐ and sixfold‐coordinated Ba atoms, linked by oxalate groups. The Zr atom, the two Ba atoms and one water O atom lie on crystallographic twofold axes, so that each coordination polyhedron has imposed C2 symmetry. Packing in the crystal is also assumed through hydrogen bonds.     

Dynamics of the barium-molecule system within large argon clusters

The effects of adding molecules on the LIF at 540 nm of a barium atom at the surface of an argon cluster (average size 420) has been investigated. We showed that molecules like ethanol,n-hexane and O₂ from stable complexes with ground state barium. In the case of molecules like N₂, CH₄ and SF₆, the collisional quenching of solvated Ba(¹ P) is observed. The large quenching rates obtained are interpreted by a surface mobility of the collisional partners. Moreover, we showed that this collisional quenching leads to the ejection of free Ba(³ P ₁).     

Structure and Magnetism of Hybrid Fe and Co Nanoclusters up to N?≤?7 Atoms

The structural and magnetic properties of small gas-phase Fe _m Co _n clusters with m?+?n ranging between 2 and 7 atoms are investigated using spin-polarized density functional theory. For a given cluster size possible compositions are subject to optimization using a variety of initial structures. The geometry, bond lengths, binding energies and magnetization are reported for the lowest energy structures. The results show that a magnetization peak occurs for Fe₄, while for hybrid clusters, switching a cobalt atom with an iron atom increases the cluster’s total magnetization by 1?μ _B . Our structural predictions are generally in agreement with other theoretical results; the origin of the discrepancies arising in some cases is discussed.     

Hydrogen bonding and structure of Ba2Ru2Cl10O·10H2O

Dibarium μ‐oxido‐bis[pentachloridoruthenate(IV)] decahydrate, Ba₂Ru₂Cl₁₀O·10H₂O, has been prepared from ruthenium(III) chloride and barium chloride in hydrochloric acid. It crystallizes in the monoclinic system (space group C2/c). The structure consists of alternating layers of [Ru₂Cl₁₀O]⁴⁻ and [Ba(H₂O)₇]²⁺ complex ions along the a direction. The O atom bonded to ruthenium occupies the 4e site, with symmetry, while the other atoms occupy general 8f sites. The overall structure is held together by O—H...O hydrogen bonds and O—H...Cl dipole–dipole interactions.     

Experimental and theoretical studies of the reaction Ba+(D2, D)BaD+: sequential impulse model for endothermic reactions

The sequential impulse model for direct reactions of Mahan, Ruska and Winn is extended to include endothermic reactions. The model is outlined and used to predict the variation in cross section with kinetic energy for heavy atom—light homonuclear diatom reactions. The results are found to agrees well with experimental data for the reaction Ba⁺(D₂, D)BaD⁺. The bond dissociation energy of BaD⁺, 2.5 ± 0.1 eV, and the proton affinity of Ba, 250 ± 3 kcal/mol, are derived.     

Electron attachment to oxygen and oxygen/ozone clusters studied in a high-resolution crossed beams experiment

Highly monochromatized electrons (with 30 meV FWHM) are used in a crossed beams experiment to investigate electron attachment to oxygen clusters (O₂)_n at electron energies from approximately zero eV up to 2 eV. At energies close to zero the attachment cross section for the reaction (O₂)_n +e → O ₂ ^? varies inversely with the electron energy, indicative of s-wave electron capture to (O₂)_n. Peaks in the attachment cross section present at higher energies can be ascribed to vibrational levels of the oxygen anion. The vibrational spacings observed can be quantitatively accounted for. In addition electron attachment to mixed oxygen/ozone clusters has been studied in the energy range up to 4 eV. Despite the initially large excess of oxygen molecules in the neutral clusters the dominant attachment products are undissociated cluster ions (O₃) _m ^? including the O ₃ ^? monomer while oxygen cluster ions (O₂) _n ^? appear with comparatively low intensity.     

Simple Access to the Heaviest Alkaline Earth Metal Hydride: A Strongly Reducing Hydrocarbon‐Soluble Barium Hydride Cluster

Reaction of Ba[N(SiMe₃)₂]₂ with PhSiH₃ in toluene gave simple access to the unique Ba hydride cluster Ba₇H₇[N(SiMe₃)₂]₇ that can be described as a square pyramid spanned by five Ba²⁺ ions with two flanking BaH[N(SiMe₃)₂] units. This heptanuclear cluster is well soluble in aromatic solvents, and the hydride ¹H NMR signals and coupling pattern suggests that the structure is stable in solution. At 95 °C, no coalescence of hydride signals is observed but the cluster slowly decomposes to undefined barium hydride species. The complex Ba₇H₇[N(SiMe₃)₂]₇ is a very strong reducing agent that already at room temperature reacts with Me₃SiCH=CH₂, norbornadiene, and ethylene. The highly reactive alkyl barium intermediates cannot be observed and deprotonate the (Me₃Si)₂N⁻ ion, as confirmed by the crystal structure of Ba₁₄H₁₂[N(SiMe₃)₂]₁₂[(Me₃Si)(Me₂SiCH₂)N]₄.