In Situ Pyrolysis Tracking and Real‐Time Phase Evolution: From a Binary Zinc Cluster to Supercapacitive Porous Carbon

The in situ tracking of the pyrolysis of a binary molecular cluster [Zn₇(μ₃‐CH₃O)₆(L)₆][ZnLCl₂]₂ is presented with one brucite disk and two mononuclear fragments (L=mmimp: 2‐methoxy‐6‐((methylimino)‐methyl)phenolate) to porous carbon using TG‐MS from 30 to 900 °C. Following up the spilled gas product during the decomposed reaction of zinc cluster along the temperature rising, and in conjunction with XRD, SEM, BET and other materials characterization, where three key steps were observed: 1) cleavage of the bulky external ligand; 2) reduction of ZnO and 3) volatilization of Zn. The real‐time‐dependent phase‐sequential evolution of the remaining products and the processing of pore forming template transformation are proposed simultaneously. The porous carbon structure featuring a uniform nano‐sized pore distribution synthesized at 900 °C with the highest surface area of 1644 m² g^?1 and pore volume of 0.926 cm³ g^?1 exhibits the best known capacitance of 662 F g^?1 at 0.5 A g^?1.     

Cyclic Octamer of Hydroxyl-functionalized Cations with Net Charge Q=+8e Kinetically Stabilized by a ‘Molecular Island’ of Cooperative Hydrogen Bonds

Cyclic octamers are well-known structural motifs in chemistry, biology and physics. These include covalently bound cyclic octameric sulphur, cylic octa-alkanes, cyclo-octameric peptides as well as hydrogen-bonded ring clusters of alcohols. In this work, we show that even calculated cyclic octamers of hydroxy-functionalized pyridinium cations with a net charge Q=+8e are kinetically stable. Eight positively charged cations are kept together by hydrogen bonding despite the strong Coulomb repulsive forces. Sufficiently long hydroxy-octyl chains prevent “Coulomb explosion” by increasing the distance between the positive charges at the pyridinium rings, reducing the Coulomb repulsion and thus strengthen hydrogen bonds between the OH groups. The eightfold positively charged cyclic octamer shows spectroscopic properties similar to those obtained for hydrogen-bonded neutral cyclic octamers of methanol. Thus, the area of the hydrogen bonded OH ring represents a ‘molecular island’ within an overall cationic environment. Although not observable, the spectroscopic properties and the correlated NBO parameters of the calculated cationic octamer support the detection of smaller cationic clusters in ionic liquids, which we observed despite the competition with ion pairs wherein attractive Coulomb forces enhance hydrogen bonding between cation and anion.     

Reactivity of Cobalt-Fullerene Complexes towards Deuterium

The adsorption of molecular deuterium (D₂) onto charged cobalt-fullerene-complexes Co_nC₆₀⁺ (n=1–8) is measured experimentally in a few-collision reaction cell. The reactivity is strongly size-dependent, hinting at clustering of the transition metal atoms on the fullerenes. Formation and desorption rate constants are obtained from the pressure-dependent deuterogenation curves. DFT calculations indeed find that this transition metal clustering is energetically more favorable than decorating the fullerene. For n=1, D₂ is predicted to bind molecularly and for n=2 dissociative and molecular configurations are quasi-isoenergetic. For n=3–8, dissociation of D₂ is thermodynamically preferred. However, reaching the ground state configuration with dissociated deuterium on the timescale of the experiment may be hindered by dissociation barriers.     

Predicting the Photoelectron Spectra of Quasi Octahedral Al6Mo- Cluster

We have recently developed a computational methodology to separate the effects of size, composition, symmetry and fluxionality in explaining the experimental photoelectron spectra of mixed-metal clusters. This methodology was successfully applied first in explaining the observed differences between the spectra of Al₁₃^- and Al₁₂Ni^- and more recently to explain the measured spectra of Al_nMo^-, n=3–5,7 clusters. The combination of our approach and new synthesis techniques can be used to prepare cluster-based materials with tunable properties. In this work we use the methodology to predict the spectrum of Al₆Mo^-. This system was chosen because its neutral counterpart is a perfect octahedron and it is distorted to a D_3d symmetry and was not observed in the recent experiments. This high symmetry cluster bridges the less symmetric Al₅Mo^- and Al₇Mo^-structures.The measured spectra of Al₅Mo^- has well defined peaks, while that of Al₇Mo^-does not. This can be explained by the fluxionality of Al₇Mo^-, as at least 6 different structures lie within the range that can be reached by thermal effects. We predict that Al₆Mo^- has well defined peaks, but some broadening is expected as there are two low-lying isomers, one of D_3d and the second of D_3h symmetry that are only 0.052 eV apart.     

Mechanisms of silicon sputtering and cluster formation explained by atomic level simulations

In low‐energy secondary ion MS, collision cascades result in rare sputter events or unfavourably low sputter yields. To better identify the origin of emission products generated by low‐energy ion impacts, we carried out molecular dynamics simulations of the underlying collision cascades, using a reactive force field that accounts for the dynamic breaking and forming of bonds. A detailed explanation of the cluster formation and ejection processes for atomic oxygen and also atomic silicon bombardment of Si (100) is given for comparison. Copyright © 2014 John Wiley & Sons, Ltd.     

Superoxide Formation on Isolated Cationic Gold Clusters

Gold nanoparticles are known to be highly versatile oxidation catalysts utilizing molecular oxygen as a feedstock, but the mechanism and species responsible for activating oxygen remain unclear. The reaction between unsupported cationic gold clusters and molecular oxygen has been investigated. The resulting complexes were characterized in the gas phase using IR spectroscopy. A strong red‐shift in the observed ν(O‐O) stretching frequency indicates the formation of superoxo (O₂^?) moieties. These moieties are seen to form spontaneously in systems, which upon electron transfer attain a closed shell within the spherical jellium model (Au₁₀⁺ and Au₂₂⁺), whereas an oxygen induced self‐promotion in the activation is observed for other systems (Au₄⁺, Au₁₂⁺, Au₂₁⁺).     

Superbenzene–Porphyrin Conjugates

A free‐base porphyrin carrying two hexabenzocoronene (HBC) substituents in a trans arrangement and its zinc complex have been prepared. The compounds were characterized extensively and found to form tricationic dimers in the gas phase. X‐ray crystallography confirms for the zinc complex a profound π‐stacking of the HBC moieties. In contrast, the free‐base porphyrin incarcerates n‐heptane which essentially prevents π‐stacking. Upon excitation of the HBC substituents, efficient energy transfer to the central porphyrin is observed.     

Crown‐Ether‐Like Structures Derived from a Ti8O8(Carboxylate)16 Metallacycle

Mixed‐metal clusters have been obtained from the reaction of titanium alkoxides with either strontium or lead acetate and methacrylic acid. The structures of the clusters are derived from the metallacycle Ti₈O₈(methacrylate)₁₆. The Sr and Pb atoms in Sr₂Ti₈O₈X₂(OOCMe)₂(methacrylate)₁₆ (X: acetate or OiPr) and Pb₂Ti₈O₈(OBu)₂X₂(methacrylate)₁₆(BuOH)₂ (X: acetate or methacrylate) occupy the central cavity of the Ti₈O₈ ring. In addition to the crown‐ether‐like coordination of the ring oxygen atoms to the Sr or Pb atoms, bridging carboxylate ligands support the coordination of the latter atoms. In the compound Pb₂Ti₆O₅(OiPr)₃X(methacrylate)₁₄ (X: OiPr or methacrylate), the lead atoms are coordinated by a fragment of the Ti₈O₈(methacrylate)₁₆ metallacycle.     

The structure of {[Co(pht)(bpy)(H2O)]·3H2O}n (pht is phthalate and bpy is 4,4′‐bipyridine) and the role of solvent water clusters in structure stability

The Co^II cation in poly[[aqua(μ‐benzene‐1,2‐dicarboxylato‐κ³O¹,O²:O¹)(μ‐4,4′‐bipyridine‐κ²N:N′)cobalt(II)] trihydrate], {[Co(C₈H₄O₄)(C₁₀H₈N₂)(H₂O)]·3H₂O}_n, is octahedrally coordinated by two N atoms of two 4,4′‐bipyridine ligands, three O atoms from phthalate anions and a fourth O atom from a coordinated water molecule. The packing consists of planes of coordination polymers linked by hydrogen bonds mediated by three solvent water molecules; the linkage is achieved by the water molecules forming intricate oligomeric clusters which also involve the O atoms of the phthalate ligands.     

A theoretical study of the effects of transition metal dopants on the adsorption and dissociation of hydrogen on nickel clusters

The structure, stability, adsorption, and dissociation of H₂ on nickel clusters doped with late transition metals were investigated using density functional theory with the BP86 functional. Molecular hydrogen physisorption occurred at a vertex atom with a low coordination number. Charge transfer between clusters and the H₂ molecule stabilized the physisorption. The chemisorption of H₂ occurred at the bridge sites, without any structural or spin change of the clusters. Among the pentamer clusters, Cd, Zn, and Au had the lowest chemisorption energies, while Ir and Pt had higher chemisorption energies for hydrogen. The computed reaction energies and activation barriers for the dissociation mechanism showed that dopants such as Rh, Pd, Pt, and Au have endothermic reaction energies and low activation barriers. This facilitates the reversible adsorption/dissociation of the H₂ molecule on these metal‐doped clusters. The dopant atoms play a major role in modulating the physisorption, chemisorption, and dissociation mechanism of H₂ on nickel clusters. © 2013 Wiley Periodicals, Inc.