Planar Clusters Research Articles

First-principles study of the adsorption of Au atoms and Au2and Au4clusters on FeO/Pt(111)

Adsorption of Au atoms and Au-2 and Au-4 clusters on Pt(111)-supported bilayer FeO film were studied using first-principles density functional theory. For atom adsorption on the FeO/Pt(111) coincidence lattice, two types of adsorption were found, in agreement with previous studies. One is that the Au atom binds with one Fe cation lifted from underneath to the top of the oxygen layer (flipped adsorption), and the other is that the Au atom adsorbs directly on the oxygen layer (direct adsorption). Flipped adsorption was found to be energetically most favored in all domains of the Moire superstructure, while direct adsorption was either metastable or unstable. The charge of the Au adatom is negative for the flipped adsorption and positive for the direct adsorption. For the Au2 and Au4 clusters, the global most stable adsorption configurations on the FeO/Pt(111) were explored, and the results indicated that one-dimensional (dimer) or two-dimensional (Au-4) upright configurations of direct adsorption were energetically preferred over the flat or three-dimensional ones throughout the Moire superstructure. Moreover, it was found that the configurations of Au-2 dimers and Au-4 clusters on FeO/Pt(111) is tightly related to the interfacial interaction including two effects: the direction-dependent reactivity of a planar Au cluster and the interfacial electrostatic interaction between the Au clusters and the FeO/Pt(111) support. The role of relativistic effects in the configuration of Au clusters and the interaction with FeO/Pt(111) were illustrated. The evolution of small Au cluster configuration on FeO/Pt(111) was discussed.

Two-Dimensional Bimetallic Carbonyl Cluster Complexes with New Properties and Reactivities

The new electron-rich, anionic, planar cluster complex [IrRu(6)(CO)(23)](-), 5, isolated as a PPN salt, PPN = [Ph(3)PNPPh(3) ](+), has been synthesized and characterized crystallographically. The complex exhibits unusual absorption and emission properties. Computational analyses have been performed to explain its metal-metal bonding and electronic properties. Anion 5 reacts with [Ph(3)PAu][NO(3)] to yield the uncharged planar complex Ru(5)Ir(CO)(20)AuPPh(3), 6, by metal atom substitution.

Anions of Xenon Clusters Bound by Long-Range Electron Correlations

In contrast with the single atom, atomic van der Waals clusters can form stable anions where the excess electron is bound due to long-range correlations with the electrons of the cluster. We report on extensive all-electron many-body ab initio studies on Xe clusters. Three-dimensional, planar, and linear structures of the clusters are investigated and compared. In particular, we find that the minimal number of Xe atoms in the cluster required to form a stable anion is 5 independently of the dimensionality of the cluster. We provide electron affinities for clusters made of 5, 6, and 7 atoms in all dimensions and find that the planar clusters form the most stable anions. The Dyson orbitals of the excess electrons are computed and analyzed.

Valence isoelectronic substitution in the B8− and B9− molecular wheels by an Al dopant atom: Umbrella-like structures of AlB7− and AlB8−

The structures and the electronic properties of two aluminum-doped boron clusters, AlB(7)(-) and AlB(8)(-), were investigated using photoelectron spectroscopy and ab initio calculations. The photoelectron spectra of AlB(7)(-) and AlB(8)(-) are both broad, suggesting significant geometry changes between the ground states of the anions and the neutrals. Unbiased global minimum searches were carried out and the calculated vertical electron detachment energies were used to compare with the experimental data. We found that the Al atom does not simply replace a B atom in the parent B(8)(-) and B(9)(-) planar clusters in AlB(7)(-) and AlB(8)(-). Instead, the global minima of the two doped-clusters are of umbrella shapes, featuring an Al atom interacting ionically with a hexagonal and heptagonal pyramidal B(7) (C(6v)) and B(8) (C(7v)) fragment, respectively. These unique umbrella-type structures are understood on the basis of the special stability of the quasi-planar B(7)(3-) and planar B(8)(2-) molecular wheels derived from double aromaticity.

Sub-nanometer distances and cluster shapes in dense hydrogen and in higher levels of hydrogen Rydberg matter by phase-delay spectroscopy

The inter-atomic distances in potassium clusters of Rydberg matter (RM) at excitation levels n B = 4–8 were recently measured by phase-delay spectroscopy (Holmlid, J Nanopart Res 12: 273, 2010). Excitation levels n B < 4 with shorter inter-atomic distances exist for hydrogen clusters, and distances down to 140 pm are now measured with this light-scattering method. The clusters studied have maximum dimensions from 0.3 nm up to several tens of nm, often being planar. A weak carbon dioxide laser beam interacts with the clusters in a tunable RM cavity. A strong fringe structure is observed as a function of the end-grating angular position. Delay lengths in the clusters are derived from the fringe structure, corresponding to twice the distance between rows or planes in the clusters. Good agreement with predicted and a few previously measured distances in excitation levels n B = 1, 2, and 3 is found. Close-packing is the main structure both in planar and 3D clusters. Planar clusters are only observed for n B = 1 and 3, while 3D clusters are found in excitation levels n B = 1, 2 and 3. The cluster–cluster distance in stacks of planar clusters for n B = 2 and 3 is now observed for the first time.

On the Solid Solution Series Er15[(Fe1–xRux)8C25]: Site Preference for Substitution in the Range 0 ≤ x ≤ 0.625?

AbstractThe solid solution series Er15[(Fe1–xRux)8C25] was prepared by arc‐melting of pressed pellets of mixtures of the elements, followed by annealing at 1173 K and quenching. Powder X‐ray patterns reveal the presence of a limited solid solution phase within the composition range 0 ≤ x ≤ 0.75 (trigonal, P321). Its crystal structure contains polyanionic slabs $\rm^2_\infty$[Fe1–xRux)8(C25)45–] stacked along [001] with Er3+ ions in between. The substitutions concern a planar triangular cluster made up of six transition metal atoms and a trigonal planar complex of composition [(Fe1–xRux)(C2)3]. The single crystal structure determination of Er15[Fe4.93(1)Ru3.07C25] clearly shows that the iron atoms forming the outer triangle of the planar cluster are not affected by substitution, resulting in the chemical composition Fe3(Fe0.19(3)Ru0.81)3for the intermetallic cluster unit. According to the chemical bonding analyses, the formation of Ru–Ru bonds seems to be the driving force for this preferential site occupation. The trigonal planar complex, again, is affected by substitution: [(Fe0.68(4)Ru0.32)(C2)3]. Assuming complete substitution except for the outer triangle of the intermetallic cluster, the limiting chemical composition for the series results inEr15[(Fe3Ru5)C25] (x = 0.625). The difference to the experimental value (x = 0.75) gives reason for further investigations. The end member Er15[Ru15C25] was not observed.

How does electron delocalization affect the electronic energy? A survey of neutral poly-nitrogen clusters

The relationship between the electron delocalization and the total electronic energy of a number of neutral poly-nitrogen clusters are studied at B3LYP/aug-cc-pVDZ computational level. It is shown that increasing the electron delocalization is accompanied with decrease of the total electronic energy. However, the geometry of clusters affects the amount of energy decrease. The energy decrease in more prominent in planar and linear clusters compared with the three dimensional, cage like, clusters with the same degree of the electron delocalization. Aromaticity of clusters whose relative electron delocalizations are higher/lower than other clusters is studied by means of the Nucleus Independent Chemical Shift (NICS). It is shown that predicted aromaticity trend based on electron delocalization in these species is in line with that emerged from NICS study, i.e. magnetic aromaticity.

Deuterium Clusters D N and Mixed K–D and D–H Clusters of Rydberg Matter: High Temperatures and Strong Coupling to Ultra-Dense Deuterium

Ultra-dense deuterium D(−1) can be formed by a catalytic process from Rydberg Matter (RM) of deuterium as reported previously. Laser-induced inertial confinement fusion (ICF) has recently been observed in this material. The formation of D(−1) is now studied through experiments observing the deuterium RM clusters DN in excitation levels nB = 1, 3 and 4. These levels are intermediate in the formation process of D(−1). Laser-induced fragmentation is used, with neutral time-of-flight (TOF) and TOF–MS measurements of the kinetic energy release (KER) from the quantized Coulomb explosions (CE). Several types of pure DN clusters, mixed clusters containing both D and H atoms, and clusters containing both D and K atoms are identified. The large planar RM clusters which are common for H and K are less common for D. The neutral DN clusters are small and have high kinetic temperature, typically at 100 K instead of 10 K for KN and HN. Large DN+ clusters are only observed when an electric field is applied, probably stabilized by increased cooling. A strong coupling of the D(1) laser fragmentation signal to the ultra-dense D(−1) signal is observed, and the materials D(1) and D(−1) are two rapidly interchangeable forms of quantum fluids.

Geometric and magnetic properties of Pt clusters supported on graphene: Relativistic density-functional calculations

The geometric and magnetic structures of small Pt(n) clusters (n = 1 - 5) supported on a graphene layer have been investigated using ab initio density functional calculations including spin-orbit coupling. Pt-Pt interactions were found to be much stronger than the Pt-C interactions promoting the binding to the support. As a consequence, the equilibrium structure of the gas-phase clusters is preserved if they are deposited on graphene. However, the clusters bind to graphene only via at most two Pt-C bonds: A Pt(2) dumbbell prefers an upright position, the larger clusters are bound to graphene only via one edge of the planar cluster (Pt(3) and Pt(5)) or via two terminal Pt atoms of a bent Pt(4) rhombus. Evidently, the strong buckling of the graphene layer induced by the Pt-C bonds prevents the formation of a larger number of cluster-support bonds. As the local spin and orbital magnetic moments are quenched on the Pt atoms forming Pt-C bonds, the magnetic structure of the supported clusters is much more inhomogeneous as in the gas-phase. This leads to noncollinear magnetic structures and a strongly reduced magnetic anisotropy energy.

Molecular and Electronic Tuning of Si/Carbon Nanotube Hybrid System

In complex structures such as conjugated Si nanoparticles on carbon nanotubes (CNT), new properties arise out particle size control or nanoparticle–nanotube contact. In this work, the interaction of Si clusters (Sin, n=1–4) with metallic (5,5) single-wall carbon nanotube (SWCNT) is investigated using first principles calculations based on density functional theory, to show that electronic property of the Si/SWCNT system can change via Si–SWCNT conformation alone. Planar Si clusters on SWCNT exhibit the same metallic property regardless of size. However, once the planarity of Sin is lost, which happens when Si adsorption sites shifts towards the top and the Si–C bonds bend resulting to a buckled Sin configuration, a band gap of ∼0.32 eV in the entire Si/SWCNT system is introduced. The migration behavior of Si adatoms shows ease of cluster formation due to surface curvature. Such cluster formation can be accommodated by a distortion in the C–C bonds of CNT. Mechanism for the opening of the SWCNT band gap is presented.

Effect of Solvation on the Oxygen Reduction Reaction on Pt Catalyst

Previous models of PEM fuel cells have not explicitly considered the effect of a bulk water layer on the mechanism of the oxygen reduction reaction. The dominant mechanism is considered to be PtO2+H++e−→PtO2H, PtO2H→PtO+PtOH, PtO+H++e−→PtOH, and PtOH+H++e−→PtOH2. Using the B3LYP functional with the LANL2DZ basis set and effective core potential on Pt and the CC-pVDZ basis set on O and H with two clusters, the first a planar Pt10 cluster and the second a three-layer Pt20 cluster, we have considered the effect of a solvation model consisting of two stacked hexagonal water structures with another water in the center above a hexagon of surface Pt atoms. We find that dissociation of O2H is much less favorable on the water covered surface as compared to the bare surface unless at least one water molecule is removed to create two adjacent surface Pt atoms. We find an H2O·O2 complex, where one H2O has been turned so as to form a hydrogen bond with the O2, and this complex can be viewed as the branch point in the mechanism. O2 can be reduced to HO2, which can dissociate to OH plus O if at least one water is removed from the surface. Alternatively, we find a new low energy pathway: H2O+O2→OH+HO2, HO2+H2O→H2O2+OH, and H2O2→OH+OH. This reaction sequence is found to be all downhill or thermoneutral. We believe both of these pathways are involved in the oxygen reduction reaction in PEM fuel cells.

Uranyl carboxyphosphonates that incorporate Cd(II)

The hydrothermal treatment of UO 3, Cd(CH 3CO 2) 2·2H 2O, and triethyl phosphonoacetate results in the formation of Cd 2[(UO 2) 6(PO 3CH 2CO 2) 3O 3(OH)(H 2O) 2]·16H 2O (CdUPAA-1), [Cd 3(UO 2) 6(PO 3CH 2CO 2) 6(H 2O) 13]·6H 2O (CdUPAA-2), and Cd(H 2O) 2[(UO 2)(PO 3CH 2CO 2)(H 2O)] 2 (CdUPAA-3). CdUPAA-1 adopts a cubic three-dimensional structure constructed from planar uranyl oxide clusters containing both UO 7 pentagonal bipyramids and UO 8 hexagonal bipyramids that are linked by Cd(II) cations and phosphonoacetate to yield large cavities approximately 16 Å across that are filled with disordered water molecules. CdUPAA-2 forms a rhombohedral three-dimensional channel structure that is assembled from UO 7 pentagonal bipyramids that are bridged by phosphonoacetate. CdUPAA-3 is layered with the hydrated Cd(II) cations incorporated directly into the layers linking one-dimensional uranyl phosphonate substructures together. In this structure, there are complex networks of hydrogen bonds that exist within the sheets, and also stitch the sheets together.

Plasmon single- and multi-quantum excitation in free metal clusters as seen by photoelectron spectroscopy

Plasmons are investigated in free nanoscale Na, Mg, and K metal clusters using synchrotron radiation-based x-ray photoelectron spectroscopy. The core levels for which the response from bulk and surface atoms can be resolved are probed over an extended binding energy range to include the plasmon loss features. In all species the features due to fundamental plasmons are identified, and in Na and K also those due to either the first order plasmon overtones or sequential plasmon excitation are observed. These features are discussed in view of earlier results for planar macroscopic samples and free clusters of the same materials.

Metal encapsulation mediated planar to three dimensional structural transformation in Au-clusters: The venus flytrap effect

DFT calculations on small Au 12 clusters reveal a side-wise folding mechanism of this planar cluster in the presence of added transition-metal atoms or ions like Cr, Mo, W, V −, Nb −, Ta −, Mn +, Tc + and Re +. Such a process is highly exothermic and leads to the formation of an 18 electron closed shell structure. The barriers for such a conversion is small and the experimental strategies are proposed for favorable observation of such a process.

Planar tetrameric metal cluster formation at room temperature induced by π⋯π interactions: 3D supramolecular host containing 1D channel filled with solvent methanol

A novel tetrameric metal cluster, [La2(phen)3(2,3-pdc)(NO3)4(H2O)]2·(CH3OH)2 (2,3-pdcH2=pyridine-2,3-dicarboxylic acid, phen=1,10-phenanthroline), have been synthesized at room temperature from water–methanol mixture by mixing the reactants in stoichiometric ratio. 2,3-Pdc and their π⋯π interactions played a vital role on the construction of the core. The auxiliary ligand, phen, which blocked the outermost periphery of the molecule and their hydrophobic π⋯π interactions facilitate the formation of the tetrameric metal clusters. The tetrameric metal clusters are connected by supramolecular interactions to form 3D supramolecular metal organic host (MOSH) producing supramolecular channels along a-axis. These supramolecular channels are filled up by solvent methanol molecules. The luminescent investigations reveal that cluster complex exhibits strong blue emission.

Large ion clusters H N+ of Rydberg Matter: Stacks of planar clusters H 7

Hydrogen and alkali atoms can form low-density metallic phases, in their most well-ordered form called Rydberg Matter (RM). RM consists mainly of small six-fold symmetric planar clusters in point group D 6h as shown by rotational spectroscopy. In their “sleeping top” (dark) state they can form stacks of clusters, as recently observed by 39K nuclear spin-flip transitions. Stacks of clusters H 7 are now directly observed by TOF-MS, using a laser intensity of <10 15 W cm −2. The TOF-MS resolution is high and the excitation level is found to be n B = 1. The Coulomb explosion process giving the ions observed involves rupture of an H 7 cluster in the stack and probably also addition of a proton to a cluster stack. Further mechanisms are discussed. RM clusters of the stack type can be larger than the previously observed limit for planar RM clusters of N = 91. That no N = 7 clusters but only larger planar RM clusters were detected in previous rotational spectroscopy studies is now suggested to be due to formation of cluster stacks.

Entrapped Planar Trimetallic Carbide in a Fullerene Cage: Synthesis, Isolation, and Spectroscopic Studies of Lu3C2@C88

We report the preparation, isolation, and spectroscopic characterizations of a novel endofullerene Lu3C2@C88, where a planar trimetallic carbide cluster Lu3C2 is encapsulated by D2-symmetric C88 ca...

Understanding Structure, Size, and Charge Effects for the H2 Dissociation Mechanism on Planar Gold Clusters

The H2 dissociation on several planar Aunq gold clusters, with n = 4, ..., 10 and charges q = 0, ±1, has been studied in detail as a function of the nuclear configuration of the cluster and at different sites of attack. It is found that the formation of a well in the entrance channel is a necessary condition for the dissociation to occur. This well always appears in sites of Aunq where there is a defect in the electronic density with respect to that of the n neutral and isolated gold atoms or, in other words, where there is a positive charge due to the polarization of the electronic density associated to the electronic correlation. When H2 attacks on linear sides of three atoms, on the middle gold atom, the reactivity is fully determined by this entrance well. On the contrary, when attacking corners there is a second step, in which a b2 antibonding orbital crosses the a1 HOMO orbital. The b2 orbital is strongly stabilized by an important bonding overlap between the H2 and the two neighboring gold atoms or...

Diversity of Architecture of Copper(I) Coordination Polymers Constructed of Copper(I) Halides and 4-Methyl-1,2,4-Triazole-3-Thiol (Hmptrz) Ligand: Syntheses, Structures, and Luminescent Properties

Solvo(hydro)thermal reactions of CuX (X = Cl, Br, I) with 4-methyl-1,2,4-triazole-3-thiol (Hmptrz) ligand afforded four new copper(I) coordination polymers, namely, [Cu(μ4-mptrz)]n (1), [Cu(μ2-Hmptrz)(μ2-I)]n (2), [Cu12(μ4-mptrz)4(μ4-I)3(μ3-I)4(μ2-I)]n (3), and [Cu(μ2-Hmptrz)(μ2-DmptrzSS)I]n (4) (DmptrzSS = 4,4′-dimethyl-3,3′-dithiodi-1,2,4-triazole), respectively. Single-crystal X-ray diffraction revealed that compound 1 has a two-dimensional (2D) layered structure with (44·62) topology and contains meso-helical (CuS)n chains. Compound 2 features a one-dimensional (1D) chain structure constructed from an unusual inorganic [Cu(μ2-S)2Cu(μ2-I)2Cu]n chain formed from two types of four-membered Cu2(μ2-S)2 and Cu2(μ2-I)2 rings. Compound 3 is a two-dimensional (2D) structure constructed from rugby-shaped Cu6I5 and planar Cu4I3 cluster units, and two types of Cu(mptrz)2 units. The I− ion in structure 3 displays its coordination versatility with μ4-, μ3-, and μ2- bridging coordination modes. Compound 4 has a doub...

Size Matters, but Is Being Planar of Any Relevance? Electron Donor−Acceptor Properties of Neutral Gold Clusters up to 20 Atoms

The main goal of this investigation is to analyze the electron donor−acceptor properties of planar and three-dimensional gold clusters (AuN (with N = 2−20), and for this purpose, a new simple model based on density functional theory is used. Calculations at the B3LYP level permit us to determine the electrodonating (χ−) and electroaccepting (χ+) electronegativity of AuN. On the basis of this analysis, it is possible to conclude that gold clusters with an odd number of atoms are better electron acceptors and better electron donors than clusters with an even number of atoms. Likewise, planar clusters are better electron acceptors than three-dimensional ones. These parameters are used to explain previous results concerning the reactivity of neutral clusters with O2 and CO. The interaction of these neutral gold clusters with adenine−uracil (AU) and guanine−cytosine (GC) base pairs is also described. A rather particular correlation was found between χ+ or χ− and the binding energies, which indicates the useful...