Center Of Cage Research Articles

Theoretical identification of the lowest energy structure of C70−n Si n , n = 1, 2, 6, 10, and 20 heterofullerenes

We have applied DFT calculations to devise stable atomic arrangements of C70−n Si n heterofullerenes with n = 1, 2, 6, 10, and 20. In general, it seems that among the considered arrangements, C atoms that are located at the polar caps of C70 prefer to be substituted by Si atoms. In the case of C68Si2, an extensive isomer search shows that the most stable configuration is that in which the Si atoms are located at the para positions of a hexagon in a polar cap. In the highly Si-doped C70 fullerenes, C and Si atoms form separate subnetworks. Doping ten Si atoms in each cap of C70, following the most stable structure of C60Si10, leads to three distinct subnetworks, a tubular carbon belt C50 surrounded by two Si10 caps. C atoms in the tubular belt preserve the conjugated pattern of distances typical of carbon nanotubes in a regular arrangement. Nucleus-independent chemical shifts (NICS) calculated at the cage centers of heterofullerenes (−21.8 to −11.0) demonstrate that all the substituted species are aromatic, but less than C70 (−27.3). The calculated NICS values may be useful for the characterization of these heterofullerenes through their endohedral 3He chemical shifts. .

Productive Discomfort: Dialogue, Reproductive Choice and Social Justice Education at the Matilda Joslyn Gage Center

Museums in the past have been static institutions, exhibiting their collections as public displays. Today, the public has come to expect more from these institutions, seeing them as safe havens where conversations can begin. As reproductive rights have moved to the forefront of political and social debate, dialogue seems to be a step in the right direction to understanding opposing views on this issue. This article presents the process of the Matilda Joslyn Cage Center in the creation of the “Who Chooses?” dialogue as a replicable model for discussions on reproductive rights. From the grant funding to the creation of informational brochures for dialogue participants and training of the facilitators, the Cage Center project has faced surprisingly few obstacles as the project has grown organically from the mission and history of the organization. This experience has strengthened the Gage Center's resolve to present dialogue on reproductive rights as a forum for social change.

Endohedrally doping the gold cage [formula omitted] with an trivalent atom B, Al, Ga, and In: Density functional studies

The relativistic density functional calculations explore that M@Au16- (M=B, Al, Ga, and In) with M at the cage center, named as M@Au16--center, should be the most stable. The M@Au16--center (M=B, Al, Ga, and In) clusters have closed-shell electronic structures and large energy gaps. All of these properties are characteristic of a magic cluster and can be well understood by the jellium model. Therefore, we strongly suggest M@Au16--center (M=B, Al, Ga, and In) are magic clusters and promising as building blocks in developing cluster-assembled materials. The energy levels and the wavefunctions of frontier orbitals explore that the HOMOs of M@Au16--center should be partly occupied by the M atom, while the LUMOs of them should be mostly from the Au16- bodies. The difference charge densities and the natural bonding orbital charge analyses imply the Au–M bonds have both the ionic and covalent characters. Finally, the mean static linear polarizabilities and first-order hyperpolarizabilities of M@Au16--center are larger than those of Au16-, while their anisotropies of the polarizability tensors are smaller than those of Au16-. We rationalize the nonlinear properties by studying the low-energy optical absorption band obtained by employing time-dependent density functional theory.

Synthesis and X-ray Structure of Endohedral Fullerene C60 Dimer Encapsulating a Water Molecule in Each C60 Cage

Abstract Fullerene C60 dimers encapsulating one or two molecules of water in two C60 cages were newly synthesized, demonstrating almost no difference in chemical reactivity between empty C60 and H2O@C60. The X-ray structure of the doubly encapsulating dimer revealed the existance of the water molecules at the center of each C60 cage.

Adsorption of Propane and Propylene on CuBTC Metal–Organic Framework: Combined Theoretical and Experimental Investigation

A combined experimental and theoretical investigation of propane and propylene adsorption in the metal–organic framework CuBTC is presented. The dependence of adsorption enthalpies on the adsorbed amount was determined by microcalorimetry up to 8 mmol g–1 coverage (roughly C3Hn/Cu2+ ratio of 1.5). Trends observed experimentally were interpreted on the basis of accurate calculations carried out at the hybrid DFT–ab initio level. Three types of adsorption sites were identified; however, qualitatively different results were obtained for propane and propylene. Propane preferentially adsorbs at the cage center sites (−ΔH° = 43 kJ mol–1), followed by adsorption at the cage window sites (31 kJ mol–1), while the interaction with the coordinatively unsaturated sites (CUS) is relatively weak (24 kJ mol–1). On the contrary, propylene preferentially interacts with the CUS (56 kJ mol–1), while the adsorption at the cage center and cage window sites was found to be only 45 and 34 kJ mol–1, respectively. Due to the topology of CuBTC, lateral interactions are significantly more important among the adsorbates located at the cage center and cage window sites (populated in the case of propane) than among adsorbates at the CUS and cage center sites (populated in the case of propylene). Therefore, adsorption energies obtained for coverages above 6 mmol g–1 of adsorbed amount were larger for propane than for propylene. Consequently, the presence of small cages makes the CuBTC MOF less suitable for propane/propylene separation than MOFs having the Cu2+ CUS but without small cages (e.g., CPO-27).

ChemInform Abstract: New Features in Coordination Chemistry: Valuable Hints from X‐Ray Analyses of Endohedral Metallofullerenes

AbstractReview: 67 refs.

Tris(μ4-azepane-1-carbodithioato)bis(μ3-azepane-1-carbodithioato)-μ9-bromido-tetra-μ2-bromido-octacopper(I)copper(II)

The reaction of Cu(Hm-dtc)2 (H2m-dtc is azepane-1-carbodi­thioic acid), CuBr2 and methyl iso­thio­cyanate yielded the title mixed-valence nona­nuclear CuI/CuII compound, [Cu9Br5(C7H12NS2)5] or [CuI 8CuIIBr5(Hm-dtc)5], encapsulating a bromide anion in the center of the Cu9Br4S10 cluster cage. The cage consists of a mononuclear CuII unit [Cu(Hm-dtc)2], three μ4-bridging Hm-dtc− ligands, eight CuI ions with distorted tetra­hedral or trigonal pyramidal coordination geometries and four μ2-bridging bromide anions. The incorporated central bromide anion inter­acts with nine Cu ions with shorter Cu—Br separations than the sum of the van der Waals radii for Cu and Br.

Water proton configurations in structures I, II, and H clathrate hydrate unit cells

Position and orientation of water protons need to be specified when the molecular simulation studies are performed for clathrate hydrates. Positions of oxygen atoms in water are experimentally determined by X-ray diffraction analysis of clathrate hydrate structures, but positions of water hydrogen atoms in the lattice are disordered. This study reports a determination of the water proton coordinates in unit cell of structure I (sI), II (sII), and H (sH) clathrate hydrates that satisfy the ice rules, have the lowest potential energy configuration for the protons, and give a net zero dipole moment. Possible proton coordinates in the unit cell were chosen by analyzing the symmetry of protons on the hexagonal or pentagonal faces in the hydrate cages and generating all possible proton distributions which satisfy the ice rules. We found that in the sI and sII unit cells, proton distributions with small net dipole moments have fairly narrow potential energy spreads of about 1 kJ∕mol. The total Coulomb potential on a test unit charge placed in the cage center for the minimum energy∕minimum dipole unit cell configurations was calculated. In the sI small cages, the Coulomb potential energy spread in each class of cage is less than 0.1 kJ∕mol, while the potential energy spread increases to values up to 6 kJ∕mol in sH and 15 kJ∕mol in the sII cages. The guest environments inside the cages can therefore be substantially different in the sII case. Cartesian coordinates for oxygen and hydrogen atoms in the sI, sII, and sH unit cells are reported for reference.

C58 on Au(111): A scanning tunneling microscopy study

C58 fullerenes were adsorbed onto room temperature Au(111) surface by low-energy (~6 eV) cluster ion beam deposition under ultrahigh vacuum conditions. The topographic and electronic properties of the deposits were monitored by means of scanning tunnelling microscopy (STM at 4.2 K). Topographic images reveal that at low coverages fullerene cages are pinned by point dislocation defects on the herringbone reconstructed gold terraces (as well as by step edges). At intermediate coverages, pinned monomers act as nucleation centres for the formation of oligomeric C58 chains and 2D islands. At the largest coverages studied, the surface becomes covered by 3D interlinked C58 cages. STM topographic images of pinned single adsorbates are essentially featureless. The corresponding local densities of states are consistent with strong cage-substrate interactions. Topographic images of [C58]n oligomers show a stripe-like intensity pattern oriented perpendicular to the axis connecting the cage centers. This striped pattern becomes even more pronounced in maps of the local density of states. As supported by density functional theory, DFT calculations, and also by analogous STM images previously obtained for C60 polymers [M. Nakaya, Y. Kuwahara, M. Aono, and T. Nakayama, J. Nanosci. Nanotechnol. 11, 2829 (2011)], we conclude that these striped orbital patterns are a fingerprint of covalent intercage bonds. For thick C58 films we have derived a bandgap of 1.2 eV from scanning tunnelling spectroscopy data confirming that the outermost C58 layer behaves as a wide band semiconductor.

First principle structural determination of (B2O3)n (n = 1–6) clusters: From planar to cage

The structure of (B2O3)n clusters (n = 1-6) are investigated using the method combining the genetic algorithm with density functional theory. Benchmark calculations indicate that TPSSh functional is reliable in predicting the energetic sequences of different isomers of (B2O3)n cluster compared to the high-level coupled cluster method. The global minimum (GM) structures of (B2O3)n clusters are planar up to n = 3, and cages at n = 4-6. A Td fullerene is found in the GM structure at n = 6. The stability of three-dimensional structures increases with the size of the cluster according to the analysis of the calculated atomization energy. Natural bonding analysis given by adaptive natural density partitioning reveals delocalized π-bonding in the 4-membered and 6-membered rings, and it is aromatic at the centers of cages and rings.

Isomers of C12N12 as potential hydrogen storage materials and the effect of the electric field therein

The relative stability, aromaticity and hydrogen storage ability of different C12N12 isomers are computationally assessed at B3LYP/6-31G(d), DFT-D-B3LYP/6-31G(d) and M052X/6-311+G(d,p) levels of theory. A negative nucleus independent chemical shift at the cage center [NICS(0)] and a high value for the gas phase heat of formation justify the stability as well as efficacy of these C12N12 isomers as promising high-energy density materials (HEDMs). Each nitrogen site is found to adsorb one hydrogen molecule which corresponds to a gravimetric density of 7.2 wt%. The temperature–pressure plot of the Gibbs free energy change separates the thermodynamically spontaneous regions of the hydrogen adsorption and desorption processes. The application of an external electric field increases the binding energy of hydrogen adsorption by ∼0.50 kcal mol−1. One of the C12N12 isomers is the basic building block involved in the formation of two different kinds of one-dimensional cluster assembled materials.

The insertion of gas molecules into polyhedral oligomeric silsesquioxane (POSS) cages: understanding the energy of insertion using quantum chemical calculations

Density functional theory (DFT) calculations using the B3LYP and ωB97XD functionals and Møller-Plesset (MP2) calculations have been used to determine the energy of insertion of seven molecules (CO2, N2, O2, CO, CH4, He and H2O) into two sizes of polyhedral oligomeric silsesquioxane (POSS) cages, T10 and T12. Geometry optimization results of each molecule inserted into the center of the POSS cage and transition-energy searches of the molecules in the largest face of both T10 and T12 (identified as the Si5 face) are discussed. The main factors that affect the energy of a molecule in a particular POSS cage are the size (number of atoms) and shape of the POSS cage and the strength of dispersion and electrostatic interactions. The largest of the molecules, CO2 and CH4, have the largest interaction energies within the center and the face of the T10 and T12 cages. Interaction energies for the diatomic molecules increase in the order H2 < O2 < N2 ∼ CO and differences between interaction energies can be attributed, in part, to differences in electron transfer between the cage and molecule. Electrostatic interactions also play a significant role in determining the interaction energy. For example, H2 and He are only slightly charged when inside the POSS cages, providing little repulsive or attractive interactions, while polar CO provides significant repulsive interaction. In the case of water, the interaction energies are low because of hydrogen bonding between the water hydrogen atoms and the POSS oxygen atoms. The interaction energies of the absorbates at the center of T12 are typically smaller than for T10 due to the larger cavity size of T12. The Si5 face has the same basic structure for both T10 and T12 cages and, consequently, the interaction energies of the absorbate molecules at the face are similar. Interaction energies obtained using MP2 calculations are lower than those obtained from DFT calculations depending on the choice of the functional. For example, use of the ωB97XD functional that treats dispersion interactions more completely than the B3LYP functional, produces values closer to the MP2 values. These results, therefore, suggest that dispersion is important in the interaction between small molecules and POSS cages.

On the magnetic behavior of spherical aromatic compounds. Insights from the closo-[B12H12]2− cluster through chemical shift tensor maps

We employ density functional methods in order to gain a deeper understanding into the magnetic behavior of the archetypal closo-[B12H12]2− cluster revealing the axis dependence of the spherical aromaticity phenomena through the graphical representation of the induced magnetic field. The analysis of the different components of the through-the-space chemical shift tensor (δij, i,j=x,y,z), given by the anisotropic shielding surface (δaniso) introduced here, allows to recognize anisotropic zones arising from the spherical aromatic behavior in conjunction to the expected isotropic region observed as a sphere of radius 0.6Å confined at the center of the icosahedral cage.

Encapsulation of transition metals in aluminum nitride fullerene: TM@(AlN)12 (TM = Ti, Mn, Fe, Co, and Ni)

The structure and stability of endohedral TM@(AlN)12 (TM = Ti, Mn, Fe, Co, Ni) complexes are studied at the level of density functional theory. It is found that complexes with TM = Mn, Fe, and Ni are energy minimum structures with TM at the cage center in Th symmetry, while those with TM = Ti and Co have more negative inclusion energies and the off-centered structures with TM placed towards one hexagon face in C1 symmetry. The calculations predict that the HOMO and LUMO energy gap of TM@(AlN)12 differs from those of the (AlN)12 cage and a free TM atom. The amount of charge that is transferred from the encapsulated guests to the cage increases with the atomic radius. The electronic and magnetic properties of TM@(AlN)12 are discussed.

Exploring the electronic and magnetic properties of C60 fullerene dimers with ladderane-like hexagonal bridges

A density functional study has been performed at B3LYP/6-31G(d) level of theory to investigate the electronic and magnetic properties of the dumbbell-like structures of fullerene dimers with boron-nitride hexagonal bridges C108(BN)3n+6, and their carbon counterparts C120+6n, n=1–10. Interestingly enough, independent of the type and size of hexagonal bridge, the dumbbell-like structures of fullerene dimers represent a short range of negative NICS values (−11.4 to −13.8ppm) calculated at the cage centers. Moreover, the computed variations of NICS values show that magnetic field decreases by going from the cage centers of fullerene dimers toward the ring centers of hexagonal bridge units. Magnetic field detects different behaviors inside the boron-nitride and carbon hexagonal bridges, an antiaromatic character in the C120+6n and almost non-aromatic character in the C108(BN)3n+6 compounds. The HOMO–LUMO gap as a function of the number of bridge hexagonal units follows a decreasing zigzag pattern in the C120+6n while in the C108(BN)3n+6 compounds it shows an upward trend up to C108(BN)12, and then remains constant until the formation of C108(BN)30. Moreover, binding energies for the C108(BN)3n+6 compounds are always lower than those of the C120+6n compounds and decrease linearly for both types of the fullerene dimers when the size of the hexagonal bridge increases.

Cylindrical Waveguide Electromagnetic Exposure System for Biological Studies with Unrestrained Mice at 1.9 GHz

This paper presents the development of an in vivo exposure system for exposing small rodents. The system consists of four identical cylindrical waveguide chambers, each with a plastic cage for housing the animal. The chamber is fed by circularly polarized radiofrequency power in the 1.9 GHz cellular frequency band and is vertically mounted so that the long axis of the animal is co-planar with the rotating incident electric field. Power sensors were used along with directional or hybrid couplers and a digital voltmeter for data acquisition for real-time dose rate monitoring. The system was tested to evaluate its dose rate performance when a mouse phantom or a mouse cadaver was inside the cage. The dose rate was quantified in terms of whole-body-average (WBA) specific absorption rate (SAR) per input power using both measurement and computational methods. The exposures of the mouse phantom and cadaver were evaluated for various possible postures and positions. The measurement results showed that the highest WBA-SAR was 16.9 W kg per 1 W incident power when the cadaver was lying prone against the cage wall and the lowest WBA-SAR was 10.4 W kg per 1 W incident power when the cadaver was standing upright in the cage center. These results were found to be in good agreement with those obtained from the computational method.

A computational NICS and 13C NMR characterization of the substitution patterns of C70−2x(BN)x fullerenes (x=1–25)

A density functional study has been performed to investigate the electronic and magnetic properties of BN substituted fullerenes C70−2x(BN)x (x=1, 2, 3, 6, 9, 12, 15, 17, 19, 21, 23 and 25) based on the NMR parameters and NICS index. The calculated 13C chemical shielding (CS) tensors are found to be perturbed at the first and second neighbors of the doped atoms while the other distant carbon atoms not to be influenced significantly. 13C Chemical shifts (δiso) of the second neighbors of nitrogen and boron are significantly shifted to upfield and downfield (the second neighboring effects), respectively. Besides, chemical shifts are also affected by the curvature of the corresponding sites; for example, the perturbed sites at the caps yield smaller absolute values of chemical shifts than those located at the equator. Nucleus independent chemical shifts (NICS) at the cage centers of heterofullerenes (from −25.29 to −8.80) demonstrate that all the substituted species are aromatic, but less than C70 (−27.29). The predicted NICS values may be useful for identification of the heterofullerenes through their endohedral 3He NMR chemical shifts.

New features in coordination chemistry: Valuable hints from X-ray analyses of endohedral metallofullerenes

The cage-like structure of fullerenes enables a new strategy for derivatization, that is, endohedral doping with metallic species. Distinctly different from exohedral metal-fullerene complexes, endohedral metallofullerenes (EMFs) show several new features in metal–carbon interactions which result from the electron transfer from the internal metallic species to the outer carbon cage. Taking advantage of recent achievements in the X-ray crystallographic characterization of EMFs, it was revealed that the single metal cation in mono-EMFs are always apart from the cage center, coordinating with the cage from inside, dominantly via electrostatic interactions, whereas the metal–cage interactions are much weaker in di-EMFs, featuring a moving dimetallic cluster in most cases. Moreover, formation of various metallic cluster species inside the fullerene cage suggest that the strong coordination ability of rare earth metals which always requests a maximal coordinated stereo environments, is a critical factor controlling the formation of stable EMF compounds. Finally, the structural features of the fullerene cage, such as the symmetry, the shape and the size, are also found to exert fundamental influences on the metal location or motion.

A DFT study on the structural and electronic properties of Td and C2 symmetry C24X4 and C22X6 heterofullerenes (X = B, Al, N, and P)

DFT calculations are applied to compare and contrast heteroatom doped Td and C2 symmetry C24X4 and C22X6 (X=B, Al, N, and P) heterofullerenes. Vibrational frequency analysis confirms that all of the systems are true minima. Probing the geometries show the alteration of CC double bonds to accommodate heteroatoms in the fullerene cage. The calculated binding energies of 6.54 and 6.39eV/atom for C24N4 and C22N6, respectively, reveal them as the most stable heterofullerenes. Evaluating nucleus independent chemical shifts at the cage centers clearly show the high aromatic character of N-doped fullerenes (−29.33 and −24.16ppm compared to +2.09 for the sole carbon cage).

Exploring electronic structures for the most stable isomers of C12B6N6 and B6N6C12 heterofullerenes based on NMR, NICS and NBO analysis: A DFT study

DFT calculations are applied to evaluate the effects of atomic arrangements of dopant atoms on electronic features of the most stable structures of (BC2N)6 including both C24 fullerene doped with six BN units (C12B6N6; model 1–7) and B12N12 nanocage doped with six CC units (B6N6C12; model 8–15). Our study reveals a relation between local structures, Cα, Cβ, Cγ, and Cδ within the molecules and 13C NMR signals. This is also observed with natural charges, so that the increase of negative charge on carbon is along with more shielding of corresponding carbon. All BN-substituted species (model 1–7) with the negative calculated NICS at their cage center are predicted to be aromatic, in contrast to C24 (NICS=±37). The predicted NICS values may be useful for the identification of the heterofullerenes through their endohedral 3He NMR chemical shifts.