Stable Cage Research Articles

(Invited) Stabilization of Giant Fullerene Cages By Encapsulation of Large Metallic Clusters

Giant tubular fullerenes are prototypes of finite-length end-capped carbon nanotubes (CNTs) which can be accurately characterized by single-crystal X-ray diffraction. We present here the synthesis, isolation and characterization of several novel tubular fullerene cages stabilized by the encapsulation of a large and streched La2C2 cluster, namely, La2C2@C92-C104. The La2C2 cluster no longer has butterfly configuration in large cages such as (450)-C100, Cs(574)-C102 and D3d(822)-C104 , butit adopts a twisted and nearly planar geometry, which is obviously dependent on the cage symmetry. The strong metal-cage interactions are proved to be responsible for the stabilization of these giant fullerene cages. Furthermore, the analysis of the transformation processes from large cages to the smaller ones provides crystallographic evidences for the formation mechanism of ideal CNTs from defective ones at the atomic level as probed with single-crystal crystallography, which is instructive to future works of the selective synthesis of ideal CNTs with identical diameter and chirality.

The transformation of polyoxometalates in the formation of intercluster compound [Ag41(α-SiW(10)O37)((t)BuC≡C)27(CH3CN)3][β-SiW(12)O40

We report a unique intercluster compound comprising a Ag41 cage encapsulating a divacant [α-SiW(10)O37](10-) anion and a complete [β-SiW(12)O40](4-) anion as a counteranion. Two electro-redox centers associated with the inner and outer POM anions show interesting electrochemical behaviours, because the stable Ag41 cage acts as an electron transfer mediator.

Image Acquisition and Image Processing Algorithms for Movement Analysis of Bearing Cages

Movement analyses of ball bearings with regard to stable and unstable cage motion behavior are often conducted by simulations, typically by investigating the cage whirl. Some experimental studies exist in which the cage is modified in order to capture its movement with sensors. This paper presents an image-based approach for investigating the cage motion without modifications, which in turn allows a cage motion analysis of an angular contact ball bearing under operation condition. Two new image evaluation algorithms are presented in detail and their suitability is verified by experiments on a bearing test rig.

Comparative theoretical investigation of the structures, energetics, and stabilities of C7N5H11cages.

Carbon-nitrogen cages are the focus of much research due to their potential use as high energy density materials (HEDMs). Several such cage isomers of C7N5H11, created by modifying the most stable N12 cage, were examined by performing theoretical calculations to evaluate their suitability as potential HEDMs. Calculations were carried out with density functional theory and Møller-Plesset perturbation theory (MP2) using the basis sets 6-31+G(d,p) and cc-pvdz. The relative thermodynamic stabilities of the isomers were explored in two ways: (1) the thermodynamic stability of one isomer was compared to that of another isomer based on their relative energies; (2) the kinetic stabilities of the isomers were determined by calculating the corresponding bond-breaking energies.

Stabilization of fullerene-like boron cages by transition metal encapsulation.

The stabilization of fullerene-like boron (B) cages in the free-standing form has been long sought after and a challenging problem. Studies that have been carried out for more than a decade have confirmed that the planar or quasi-planar polymorphs are energetically favored ground states over a wide range of small and medium-sized B clusters. Recently, the breakthroughs represented by Nat. Chem., 2014, 6, 727 established that the transition from planar/quasi-planar to cage-like Bn clusters occurs around n = ∼38-40, paving the way for understanding the intriguing chemistry of B-fullerene. We herein demonstrate that the transition demarcation, n, can be significantly reduced with the help of transition metal encapsulation. We explore via extensive first-principles swarm-intelligence based structure searches the free energy landscapes of B24 clusters doped by a series of transition metals and find that the low-lying energy regime is generally dominated by cage-like isomers. This is in sharp contrast to that of bare B24 clusters, where the quasi-planar and rather irregular polyhedrons are prevalent. Most strikingly, a highly symmetric B cage with D3h symmetry is discovered in the case of Mo or W encapsulation. The endohedral D3h cages exhibit robust thermodynamic, dynamic and chemical stabilities, which can be rationalized in terms of their unique electronic structure of an 18-electron closed-shell configuration. Our results indicate that transition metal encapsulation is a feasible route for stabilizing medium-sized B cages, offering a useful roadmap for the discovery of more B fullerene analogues as building blocks of nanomaterials.

Isolated pentagon rule violating endohedral metallofullerenes explained using the Hückel rule: a statistical mechanical study of the C84 Isomeric Set.

Fullerenes and their structure and stability have been a major topic of discussion and research since their discovery nearly 30 years ago. The isolated pentagon rule (IPR) has long served as a guideline for predicting the most stable fullerene cages. More recently, endohedral metallofullerenes have been discovered that violate the IPR. This article presents a systematic, temperature dependent, statistical thermodynamic study of the 24 possible IPR isomers of C84 as well as two of the experimentally known non-IPR isomers (51365 and 51383), at several different charges (0, -2, -4, and -6). From the results of this study, we conclude that the Hückel rule is a valid simpler explanation for the stability of fused pentagons in endohedral metallofullerenes.

ChemInform Abstract: First Isomers of Pristine C104 Fullerene Structurally Confirmed as Chlorides, C104(258)Cl16 and C104(812)Cl24.

Isolation and characterization of very large fullerenes is hampered by a drastic decrease of their content in fullerene soot with increasing fullerene size and a simultaneous increase of the number of possible IPR (Isolated Pentagon Rule) isomers. In the present work, fractions containing mixtures of C102 and C104 were isolated in very small quantities (several dozens of micrograms) by multi-step recycling HPLC from an arc-discharge fullerene soot. Two such fractions were used for chlorination with a VCl4/SbCl5 mixture in glass ampoules at 350–360 °C. The resulting chlorides were investigated by single-crystal X-ray diffraction using synchrotron radiation. By this means, two IPR isomers of C104, numbers 258 and 812 (of 823 topologically possible isomers), have been confirmed for the first time as chlorides, C1-C104(258)Cl16 and D2-C104(812)Cl24, respectively, while an admixture of C2-C104(811)Cl24 was assumed to be present in the latter chloride. DFT calculations showed that pristine C104(812) belongs to rather stable C104 cages, whereas C104(258) is much less stable.

Shedding light on the self-assembly of stable SiC based cage nanostructures: A comprehensive molecular dynamics study

A comprehensive molecular dynamics study to shed light on the existence of SiC based cage nanostructures SimCn, together with their stability, structural and other properties, in the range of compositions with n/(n+m) from 0.4 to 0.6 has been carried out using an efficient semi-empirical Hamiltonian scheme. Through this study, a series of self-assembled stable (even up to 2000K) SiC based SimCn cage structures are predicted. The mechanism of the stability and structural properties of the stable SimCn caged structures are analyzed in terms of their composition, bonding nature, surface environment, local strain, and types of ring structures. It is found that, for a given composition, the existence of the Si–C bonds, the sp2 bonding nature between the Si and C atoms, and the role played by the environmental mediation are crucial in forming the self-assembled and stable SiC cage structures. In particular, a “mending” process dictated by an environment-driven self-assembly is provided to show the possible transition from one stable cage structure to another cage structure of similar composition which might occur in the synthesis. The oscillatory behavior of the HOMO–LUMO gap as a function of the diameter of SimCn cages is also observed as expected. This work provides a possible path way for fabricating SiC based nano-cage structures.

Polyhedral Metal-Imidazolate Cages: Control of Self-Assembly and Cage to Cage Transformation

A series of neutral cubic nickel(II)-imidazolate Ni8L12X4 cages were prepared by rational choices of substituents and anions with solvothermal subcomponent self-assembly technology. Both substituents and halide anions play a critical role in the formation and stabilization of cubic cages. Changing one of the factors in the reaction will switch the final structure to a Ni14L24 rhombic dodecahedral cage. The cubic cage can transform to a large rhombic dodecahedral cage in the presence of methylamine at room temperature accompanied by a color change from purple to light yellow.

First Isomers of Pristine C104 Fullerene Structurally Confirmed as Chlorides, C104(258)Cl16 and C104(812)Cl24

Isolation and characterization of very large fullerenes is hampered by a drastic decrease of their content in fullerene soot with increasing fullerene size and a simultaneous increase of the number of possible IPR (Isolated Pentagon Rule) isomers. In the present work, fractions containing mixtures of C102 and C104 were isolated in very small quantities (several dozens of micrograms) by multi-step recycling HPLC from an arc-discharge fullerene soot. Two such fractions were used for chlorination with a VCl4/SbCl5 mixture in glass ampoules at 350-360 °C. The resulting chlorides were investigated by single-crystal X-ray diffraction using synchrotron radiation. By this means, two IPR isomers of C104 , numbers 258 and 812 (of 823 topologically possible isomers), have been confirmed for the first time as chlorides, C1 -C104(258)Cl16 and D2-C104 (812)Cl24, respectively, while an admixture of C2 -C104(811)Cl24 was assumed to be present in the latter chloride. DFT calculations showed that pristine C104(812) belongs to rather stable C104 cages, whereas C104(258) is much less stable.

A first-principles study of ZnO polar surface growth: Adsorption of ZnxOy clusters

Adsorption of Zn(x)O(y) (x + y = 1-6) clusters on ZnO (000 ± 1) polar surfaces is studied systematically via density function theory (DFT) calculations. Different adsorption behaviors are predicted for these two surfaces. On the (0001)-Zn surface, O atoms adsorb on hollow sites at the initial stage. Then Zn atoms come in, and the stable structure becomes bulk-like for some specific clusters. On the (0001)-O surface, Zn cluster adsorption leads to stable cage structures formed by pulling substrate O out. In clusters with both Zn and O, O atoms avoid directly bonding with the surface, and no energetically favorable bulk-like structure is found. On the basis of the prediction of these surface adsorption behaviors, experimentally observed growth rate and surface roughness differences on these two polar surfaces can be understood.

Magnetic hollow cages with colossal moments

A comprehensive study of the interaction of transition metal clusters with B, C, N, O, and Si reveal novel structure and properties: Co12C6, Mn12C6, and Mn24C18 clusters form stable ferromagnetic hollow cages with total magnetic moments of 14 μB, 38 μB, and 70 μB, respectively. Replacement of C with B, N, O, or Si has significant impact on their structure and magnetic properties. For example, Mn20Si12 cluster forms a ferrimagnetic dodecahedral hollow cage with a total magnetic moment of 36 μB while Mn12N6, X12C6 (X = Ni, Cu, Pd, Pt), and Cu12O6 possess no magnetic moment, although they retain hollow cage structures. Mn12B6 and Mn24Si18, on the other hand, form compact ferrimagnetic structures. Synthesis of hollow cage clusters with unique magnetic properties may lead to important applications.

STRUCTURE AND STABILITY OF $CLOSO-B_{n}H_{n-1}N_{2}^{-} (n=5-12)$

[Formula: see text], framework-isoelectronic to [Formula: see text], have been investigated at the B3LYP/6-311+G** level of theory. The most stable positional isomers of individual [Formula: see text] are similar to those of [Formula: see text] and [Formula: see text] in framework configuration. The energy analysis reveals that the cage [Formula: see text] with the icosahedron framework, [Formula: see text] with the octahedron framework and [Formula: see text] with the bicapped square antiprism framework are, in order, the most stable in the [Formula: see text] system. Furthermore, three-dimensional aromaticity of all [Formula: see text] is characterized. The most stable cages, [Formula: see text], [Formula: see text] and [Formula: see text], also have relatively large aromaticity. All the predicted N–N stretching frequencies (2127–2303 cm−1) of the most stable positional isomers in the [Formula: see text] system are lower than the computational N–N stretching frequency (2445 cm−1) of free N2 at the same level, which results from the σ donation of N2 to B frameworks. The stretching frequencies of N–N in the [Formula: see text] cages increase with the decrease of N–N distances or the increase of B–N distance. In addition, B n−1 H n−1 fragment has larger affinity for group CH than that for group BNN, namely, it favors to form the [Formula: see text] rather than the [Formula: see text].

Stabilization of carbon nanotubes-based hollow cages for energy storage: From collapsed morphology to free-standing structure

Novel polyaniline nanofibers/carbon nanotubes hollow cages were prepared via the layer-by-layer assembly technique on spherical templates. For the first time, we reported a facile and efficient method to stabilize the hollow structure by in situ polymerization of aniline. After that, the hollow cages were changed to be hollow microspheres, with the morphology transferred from collapsed one to free-standing one. Moreover, the shell thickness obviously increased. Raman spectra revealed that there were not only electrostatic interaction but also π–π conjugation between the polyaniline nanofibers and carbon nanotubes, and also demonstrated that the formative polyaniline resulted in the more stable structure. The maximum specific capacitance of the final product was calculated to be 514Fg−1 and 94% of its original specific capacitance remained after 500 cycles, indicating that it is a promising electrode material for high performance supercapacitors.

Supertetrahedral cubane C32H8 and supertetrahedral dodecahedrane C80H20 with tetrahedral C4H fragments in the vertices

The DFT B3LYP/6-311+G(d,p) calculations predict novel stable hydrocarbon cage structures of ‘supertetrahedral’ cubane C 32 H 8 and dodecahedrane C 80 H 20 in which the CH vertices are replaced by the tetrahedral C 4 H fragments.

ChemInform Abstract: Preparation and Characterization of Polyhedral Oligosilsesquioxanes

AbstractReview: 502 refs.

The Boron Conundrum: Which Principles Underlie the Formation of Large Hollow Boron Cages?

Extensive optimisation calculations are performed for the B(80) isomers in order to find out which principles underlie the formation of large hollow boron cages. Our analysis shows that the most stable isomers contain triangular B(10) or rhombohedral B(16) building blocks. The lowest-energy isomer has C(3v) symmetry and is characterised by a belt of three interconnected B(16) units and two separate B(10) units. At the B3LYP/6-31G(d) level of theory, this newly discovered isomer is 2.29, 1.48, and 0.54 eV below the leapfrog B(80) of Szwacki et al., the T(h) -B(80) of Wang, and the D(3d) -B(80) of Pochet et al., respectively. Our C(3v) isomer is therefore identified as the most stable hollow cage isomer of B(80) presently known. Its HOMO-LUMO gap of 1.6 eV approaches that of the leapfrog B(80). The leapfrog principle still remains a reliable scheme for producing boron cages with larger HOMO-LUMO gaps, whereas the thermodynamically most stable B(80) cages are formed when all pentagonal faces are capped. We show that large hollow cages of boron retain a preference for fullerene frames. The additional capping is in accordance with the following rules: preference for capping of pentagonal faces, formation of B(10) and/or B(16) units, homogeneous distribution of the hexagonal caps, and hole density approaching 1/9. Although our most stable B(80) isomer still remains higher in energy than the B(80) core-shell structure, we show that by applying the bonding principles to larger structures it is possible to construct boron cages with higher stabilisation energy per boron atom than the core-shell structure; a prototypical example is B(160). This clearly shows the continuous competition between the two suggested construction schemes, namely, the formation of multiple-shell structures and hollow cages.

A new hole density as a stability measure for boron fullerenes

We investigate the stability of boron fullerene sets B76, B78 and B82. We evaluate the ground state energies, nucleus-independent chemical shift (NICS), the binding energies per atom and the band gap values by means of first-principles methods. We construct our fullerene design by capping of pentagons and hexagons of B60 cages in such a way that the total number of atoms is preserved. In doing so, a new hole density definition is proposed such that each member of a fullerene group has a different hole density which depends on the capping process. Our analysis reveals that each boron fullerene set has its lowest-energy configuration around the same normalized hole density and the most stable cages are found in the fullerene groups which have a relatively large difference between the maximum and the minimum hole densities. The result is a new stability measure relating the cage geometry characterized by the hole density to the relative energy.

First-principles calculations of the electronic structure of C20, electric field, and monomer interaction effects

The density functional theory calculations are applied for C20 cage fullerenes. Furan, pyrole, and phenylvinyle monomers are made to interact with a C20 cage at the same C position. An electric field was applied with varying strength. Computations were carried out for all cases at the B3LYP/6-31G* level. The structure, energetic, and relative stabilities of the compounds were compared with each other and analyzed. In addition, the electric field dependent and independent electronic transition spectra of the proposed stable neutral C20 cage are investigated.

New nanomaterials based on In12As12cages: an ab initio bottom-up study

We report the results of density functional calculations on nanostructures of InAs, including the small InnAsn (n = 1–15) clusters, the stable hollow cage In12As12 and its derivative nanomaterials (In12As12-based dimer, trimer, nanowire, sheet, and new nanoporous crystal phase). Our results show that among the small InnAsn (n = 1–15) clusters, the In12As12 cage structure with Th symmetry and large HOMO–LUMO gap is proved to be the most stable one, indicating that it would be an ideal building block for the synthesis of cluster-assembled materials. Via the coalescence of In12As12 building blocks, we find that the In12As12 cages can bind into various nanomaterials with different dimensionality by the most stable bonding via In6As6 hexagonal faces forming intercluster hexagonal prism. All of these constructed nanostructures are found to be more stable than the individual In12As12 cage and rock salt (RS) phase of InAs. The band analysis reveals that the periodic In12As12-assembled nanomaterials have relative band gap magnitudes of 2.00–4.89 (Eg/Eg,ZB) with respect to the zinc blende (ZB) phase of InAs, and the new nanoporous polymorph holds an indirect gap of ∼0.86 eV, which may extend the range of properties and applications of the InAs compound.