Closed-cage Structures Research Articles

An Uncommon Solvent‐Controlled Photochromic Tetraphenylethylene‐Based Co‐crystal

AbstractA co‐crystal FJU‐182 with a closed cage structure with photochromic phenomenon was formed using a tetraphenylene derivatives 4,4′,4′′,4′′′‐(anthracene‐9,10‐diylidenebis(methanediyl‐ylidene))tetrabenzoic acid self‐assembled with 1,3‐di(4‐pyridyl)propane in a solvent. It was also found that isomorphic crystals grown from different solvents exhibited different fluorescence. The electron paramagnetic resonance and X‐ray photoelectron spectroscopy data showed that the photochromic mechanism of crystal FJU‐182 was due to photoinduced electron transfer, while the different color change of crystals grown from different solvents was attributed to the size of solvent molecules. The I−V curves of the crystals FJU‐182 before and after illumination were also tested, and it was found that the conductivity of the crystals before the color change would be 3–8 times higher than the conductivity of the crystals after the color development. FJU‐182 provides a new case for electrochemical devices with photoelectric response.

Statistical abundance and stability of carbon nanostructures by combined condensation-annealing molecular dynamics simulations

Molecular dynamic (MD) simulations of the Combined Condensation and Annealing (CCA) of free carbon atoms was used to investigate the statistical abundance and stability of neutral carbon nanostructures for a cluster size between 2 and 54 atoms. During these CCA MD-simulations carbon atoms are submitted to a condensation/heating phase, a CTR phase at a prescribed annealing temperature and a cooling phase. Numerical experiments showed that the determination of the statistical abundances requires at least 100 ns condensation/heating phase, 100 ns CTR phase at the annealing temperature and 100 ns cooling phase. The clusters obtained by CCA MD-simulations are dominated by linear structures for n = 2–5, mono-ring for n = 6–15, multi-ring structures for n = 16–18, 2D graphene-like structure for sizes in the range n = 19–29 and cage-like structure above n = 30. Open cage structures are obtained at temperature around 2000 K, while closed cage structures dominate at 3000 K. For even larger temperature, i.e., 4000 K, the dominant structures are 2D and 3D multi-ring structures, 2D graphene-like structure remaining quite significant. The resulting bond energy versus cluster size variation is in good agreement with those obtained by other approaches.

Short Pulse Laser Synthesis of Transition-Metal Dichalcogenide Nanostructures under Ambient Conditions.

The study of inorganic nanometer-scale materials with hollow closed-cage structures, such as inorganic fullerene-like (IF) nanostructures and inorganic nanotubes (INTs), is a rapidly growing field. Numerous kinds of IF nanostructures and INTs were synthesized for a variety of applications, particularly for lubrication, functional coatings, and reinforcement of polymer matrices. To date, such nanostructures have been synthesized mostly by heating a transition metal or oxide thereof in the presence of precursor gases, which are however toxic and hazardous. In this context, one frontier of research in this field is the development of new avenues for the green synthesis of IF structures and INTs, directly from the bulk of layered compounds. In the present work, we demonstrate a simple room-temperature and environmentally friendly approach for the synthesis of IF nanostructures and INTs via ultrashort-pulse laser ablation of a mixture of transition-metal dichalcogenides in bulk form mixed with Pb/PbO, in ambient air. The method can be considered as a synergy of photothermally and photochemically induced chemical transformations. The ultrafast-laser-induced excitation of the material, complemented with the formation of extended hot annealing regions in the presence of the metal catalyst, facilitates the formation of different nanostructures. Being fast, easy, and material-independent, our method offers new opportunities for the synthesis of IF nanostructures and INTs from different bulk metal chalcogenide compounds. On the basis of the capabilities of laser technology as well, this method could advantageously be further developed into a versatile tool for the simultaneous growth and patterning of such nanostructures in preselected positions for a variety of applications.

Confinement Effects on Water Clusters Inside Carbon Nanotubes

The effects of confinement on water clusters inside nonmetallic carbon nanotubes with radii ranging between 4 and 7.5 Å have been computationally investigated by means of global optimization and finite temperature simulations. The water–water interaction is described by the TIP4P rigid body potential, and a Lennard-Jones potential is used for the water–carbon interaction. Water clusters containing up to 20 molecules are found to form 1D chainlike configurations for the narrow (7, 5) nanotube and 2D ladderlike structures in the (7, 6) tube. In wider tubes, 3D configurations are then formed showing helical motifs, ringlike or closed cage structures, before the most stable structure on flat graphene is eventually found. The same results are obtained by replacing the fully atomistic water–nanotube potential by its continuous approximation [Bretón, J.; González-Platas, J.; Giradet, C. J. Chem. Phys.1994, 101, 3334], indicating a negligible effect of corrugation. The effects of additional nanotubes were also considered with the adsorption energies being found to converge rather quickly already for the triple-wall tube. Parallel tempering Monte Carlo simulations of the water octamer reveal a counterintuitive decrease in the melting point relative to the free-standing case. Molecular dynamics simulations show that melting is concomitant with some axial diffusion of the water molecules, and with radial diffusion perpendicular to the tube axis remaining limited. In accordance with previous studies concerned with bulk water, the weakening of the cluster thermal stability is interpreted as being caused by the hydrophobic character of the carbon–water interaction.

Structural Origin of the Antimagic Number in Protonated Water Clusters H+(H2O)n: Spectroscopic Observation of the “Missing” Water Molecule in the Outermost Hydration Shell

To investigate the origin of the instability of the water network consisting of a specific (so-called antimagic) number of molecules, we report infrared spectra of cold protonated water clusters H+(H2O)n (n = 20–23) tagged with weakly bound H2 molecules. In this size range, only in n = 22, which has been known to be an antimagic number cluster, is a band attributed to the one-coordinated, dangling water molecule observed. This observation indicates that the 22nd water molecule is loosely bound to the surface of the closed cage structure of H+(H2O)21. This band has been missing in any spectra of the warmer and bare cluster of n = 22. The present results evidence the characteristic cluster structure of the antimagic numbered cluster, which has been predicted by Singh et al. (Angew. Chem., Int. Ed.2006, 45, 3795) and suggests that the thermal and dynamic effects perturb the spectrum, structure, or both in warmer cases.

Medical applications of inorganic fullerene-like nanoparticles

Nanoparticles of layered compounds, like MoS2 and WS2, having hollow closed-cage structures and known as fullerene-like (IF) and inorganic nanotubes (INT), are synthesized in macroscopic amounts. They were found to have superior tribological properties and can serve as solid-state additives to different lubrication fluids. More recently, metallic films incorporating the IF nanoparticles were prepared via wet deposition methods and also by physical vapor deposition techniques. The incorporation of the nanoparticles endows such coatings self-lubricating behavior, i.e. low friction and wear, which is highly desirable for variety of applications. The current feature article provides a short overview of the progress in the materials synthesis of IF and INT phases. Subsequently, a progress report of the various efforts to apply such coatings to medical devices and drug delivery is described.

Closed-Cage Tungsten Oxide Clusters in the Gas Phase

During the course of a study on the clustering of W-Se and W-S mixtures in the gas phase using laser desorption ionization (LDI) mass spectrometry, we observed several anionic W-O clusters. Three distinct species, W(6)O(19)(-), W(13)O(29)(-), and W(14)O(32)(-), stand out as intense peaks in the regular mass spectral pattern of tungsten oxide clusters suggesting unusual stabilities for them. Moreover, these clusters do not fragment in the postsource decay analysis. While trying to understand the precursor material, which produced these clusters, we found the presence of nanoscale forms of tungsten oxide. The structure and thermodynamic parameters of tungsten clusters have been explored using relativistic quantum chemical methods. Our computed results of atomization energy are consistent with the observed LDI mass spectra. The computational results suggest that the clusters observed have closed-cage structure. These distinct W(13) and W(14) clusters were observed for the first time in the gas phase.

Atom by atom: HRTEM insights into inorganic nanotubes and fullerene-like structures

The characterization of nanostructures down to the atomic scale is essential to understand some physical properties. Such a characterization is possible today using direct imaging methods such as aberration-corrected high-resolution transmission electron microscopy (HRTEM), when iteratively backed by advanced modeling produced by theoretical structure calculations and image calculations. Aberration-corrected HRTEM is therefore extremely useful for investigating low-dimensional structures, such as inorganic fullerene-like particles and inorganic nanotubes. The atomic arrangement in these nanostructures can lead to new insights into the growth mechanism or physical properties, where imminent commercial applications are unfolding. This article will focus on two structures that are symmetric and reproducible. The first structure that will be dealt with is the smallest stable symmetric closed-cage structure in the inorganic system, a MoS(2) nanooctahedron. It is investigated by means of aberration-corrected microscopy which allowed validating the suggested DFTB-MD model. It will be shown that structures diverging from the energetically most stable structures are present in the laser ablated soot and that the alignment of the different shells is parallel, unlike the bulk material where the alignment is antiparallel. These findings correspond well with the high-energy synthetic route and they provide more insight into the growth mechanism. The second structure studied is WS(2) nanotubes, which have already been shown to have a unique structure with very desirable mechanical properties. The joint HRTEM study combined with modeling reveals new information regarding the chirality of the different shells and provides a better understanding of their growth mechanism.

Gas-phase synthesis of inorganic fullerene-like structures and inorganic nanotubes

Abstract Following the discovery of fullerenes (C60) and carbon nanotubes, it was shown that nanoparticles of inorganic layered compounds, like WS2 and MoS2, are unstable in the planar form and they form closed cage structures with polyhedral or nanotubular shapes. Although initially the method of synthesis for the formation of such closed caged structures and nanotubes involved starting from the respective oxides, it is now well established that the gas-phase synthetic route (using metal chlorides, carbonyls etc) provides an alternative which is suitable for the synthesis of very many closed caged structures and nanotubes hitherto unknown. Various issues with this method of synthesis, including its fundamentals, mechanism, and the properties of the inorganic fullerene-like structures produced are reviewed, together with some possible applications.

Synthesis and characterisation of MS<SUB align=right>2 (M = Nb, Ta) nanostructures

Inorganic Fullerene-like (IF) of metal dichalcogenide MS2 (M = Mo, W) materials have been synthesised and applied in some fields, analogous layered compounds, like NbS2 andTaS2, were unstable in the planar form and tend to form closed cage structures with on the polyhedral or tubular shape. The main goal of the present work was to prepare tubular MS2 (M = Nb, Ta) nanostructures by solid-phase reaction method, which was an alternative route to prepare one dimension disulfide nanomaterials. The characterisation of associated products, have been evaluated using transmission electron microscopy (TEM) and other techniques. Besides, growth process of nanostructures was discussed in detail.

Singular MoS2, SiO2and Si nanostructures—synthesis by solar ablation

Solar ablation creates the sharp radiative and temperature gradients, as well as the high-temperature annealing environment, that favor nanomaterial syntheses. Using highly concentrated sunlight, we generated fullerene-like MoS2, ranging from single-walled nanotubes and closed-cage structures to their larger multi-walled counterparts. TEM, HRTEM and EDS unambiguously established the nanostructures, some achieving fundamentally minimum sizes predicted by molecular structural theory. Irradiation of MoS2 and powdered mixtures of MoS2 + SiO2 in evacuated quartz ampoules also generated nanofibers and nanospheres of amorphous SiO2: the first production of SiO2nanostructures purely from quartz. Also, solar ablation of MoS2 + SiO mixtures produced nanowires and nanospheres of crystalline Si.

Comment on ‘Low-temperature synthesis of α-Fe 2O 3 nanoparticles with a closed cage structure’ by X. Wang et al. [Chem. Phys. Lett. 384 (2004) 391

A Letter by Wang et al. reported synthesis of α-Fe 2O 3 nanoparticles with a closed cage structure. The authors mistook thickness fringes in the transmission electron micrographs (TEM) as evidence for ‘layers’ of ‘a closed cage structure’. We prepared α-Fe 2O 3 nanoparticles using procedures described by Wang and recorded a series of TEM images of the particles at 0.5° increments in specimen tilt angle. In this Letter, we first explain the origin of thickness fringes, and then present a series of images to prove that these particles do not have a closed cage structure.

Inorganic fullerenes and nanotubes: Wealth of materials and morphologies

It is already well established today that numerous materials form closed-cage structures, of which carbon fullerenes and nanotubes are a special case [1]. Inorganic fullerene-like nanoparticles (designated IF) and inorganic nanotubes (INT) have been produced by different routes and experimental techniques, achieving persistent growth of a variety of materials and structural wealth within them. The research in this area has focused on synthesizing new IF and INT materials and understanding their different properties as well as scaling up the synthetic process in order to make it suitable for industrial applications. In this review, the main synthetic procedures to obtain inorganic fullerene-like nanoparticles and nanotubes will be discussed alongside with the different mechanisms that affect the morphology of the final product. The main differences between the morphologies will be presented. Some general considerations relating the properties of the parent compound with the morphology of the product will be mentioned.

Large‐Scale Synthesis of MoS2 Bucky Onions

The MoS2 Bucky Onions with nesting spherical layered closed-cage structure were obtained by MoS3 precursors heated at high temperature in hydrogen atmosphere. The MoS2 Bucky Onions are spherical particles with diameter ranging 60–200 nm.

Structure and Stability of Molybdenum Sulfide Fullerenes

MoS2 nanooctahedra are believed to be the smallest stable closed-cage structures of MoS2, i.e., the genuine inorganic fullerenes. Here a combination of experiments and density functional tight bind...

Structure and Stability of Molybdenum Sulfide Fullerenes

MoS2 nanooctahedra are believed to be the smallest stable closed-cage structures of MoS2, i.e., the genuine inorganic fullerenes. Here a combination of experiments and density functional tight binding calculations with molecular dynamics annealing are used to elucidate the structures and electronic properties of octahedral MoS2 fullerenes. Through the use of these calculations MoS2 octahedra were found to be stable beyond nMo > 100 but with the loss of 12 sulfur atoms in the six corners. In contrast to bulk and nanotubular MoS2, which are semiconductors, the Fermi level of the nanooctahedra is situated within the band, thus making them metallic-like. A model is used for extending the calculations to much larger sizes. These model calculations show that, in agreement with experiment, the multiwall nanooctahedra are stable over a limited size range of 104-105 atoms, whereupon they are converted into multiwall MoS2 nanoparticles with a quasi-spherical shape. On the experimental side, targets of MoS2 and MoSe2 were laser-ablated and analyzed mostly through transmission electron microscopy. This analysis shows that, in qualitative agreement with the theoretical analysis, multilayer nanooctahedra of MoS2 with 1000-25 000 atoms (Mo + S) are stable. Furthermore, this and previous work show that beyond approximately 105 atoms fullerene-like structures with quasi-spherical forms and 30-100 layers become stable. Laser-ablated WS2 samples yielded much less faceted and sometimes spherically symmetric nanocages.

Closed-cage (fullerene-like) structures of NiBr 2

It is well accepted by now that nanoparticles of inorganic layered compounds form closed-cage structures (IF). In particular closed-cage nanoparticles of metal dihalides, like NiCl 2, CdCl 2 and CdI 2 were shown to produce such structures in the past. In the present report IF-NiBr 2 polyhedra and quasi-spherical structures were obtained by the evaporation/recrystallization technique as well as by laser ablation. When the nanoclusters were formed in humid atmosphere, nickel perbromate hydrate [Ni(BrO 4) 2(H 2O) 6] polyhedra and short tubules were produced, as a result of a reaction with water. Nanooctahedra of NiBr 2 were found occasionally in the irradiated soot. The reoccurrence of this structure in the IF family suggests that it is a generic one. Consistent with previous observations, this study showed that formation of the IF materials stabilized the material under the electron-beam irradiation. The growth mechanism of these nanostructures is briefly discussed.

Novel Cage Clusters of MoS2 in the Gas Phase

Laser evaporation of MoS(2) nanoflakes gives negatively charged magic number clusters of compositions Mo(13)S(25) and Mo(13)S(28), which are shown to have closed-cage structures. The clusters are stable and do not show fragmentation in the post-source decay analysis even at the highest laser powers. Computations suggest that Mo(13)S(25) has a central cavity with a diameter of 4.5 A. The nanosheets of MoS(2) could curl upon laser irradiation, explaining the cluster formation.

A model for the role of short self‐assembled peptides in the very early stages of the origin of life

The molecular basis of the origin of life is one of the most fundamental questions in modern biology. While the "RNA world" hypothesis offers a very sensible model for the evolvement of the current biochemical networks, there is a lack of knowledge about the early steps that led to the formation of the first RNA molecules. This issue is essential as it is practically impossible that complex molecules as functional RNA oligonucleotides had evolved spontaneously. It was recently demonstrated that peptide molecules as simple as dipeptides can self-assemble into well-ordered tubular, fibrilar, and closed-cage structures. Other studies have confirmed the ability of dipeptides to act as catalysts and the capability of other peptides, as short as tripeptides, to serve as a template for nucleotide binding and orientation. Unlike complex RNA molecules, the spontaneous formation of functional short peptides in the primordial earth conditions is very likely. We suggest a novel mechanism for the origin of life that is based on the ability of short peptides to form encapsulated structures, catalyst chemical reaction, and serve as highly ordered template for the assembly of nucleotides. This model may explain the early events that led to the formation of the current biochemical machinery that combines the elaborated and coordinated interaction between nucleic acids and proteins to allow the function of living systems.

Applications of WS2(MoS2) inorganic nanotubes and fullerene-like nanoparticles for solid lubrication and for structural nanocomposites

Nanoparticles of WS2 and MoS2 with a closed cage structure (fullerene-like) that are termed IF phases are synthesized in large amounts in a pure form. These nanoparticles were shown to play a favorable role as solid lubricants under severe conditions where fluids are unable to support the heavy load and are squeezed away from the contact area. Various tribological scenarios are presented for these superior solid lubricants, demonstrating the large scale potential for applications of these materials. The mechanism of action of these solid lubricants is briefly discussed. Various other potential applications of IF phases for nanocomposites with high impact resistance; in rechargeable batteries and in optical devices are discussed in short.