C60 Cage Research Articles

Electric-dipole-coupled H2O@C60 dimer: Translation-rotation eigenstates from twelve-dimensional quantum calculations.

We report on variational solutions to the twelve-dimensional (12D) Schrödinger equation appertaining to the translation-rotation (TR) eigenstates of H2O@C60 dimer, associated with the quantized "rattling" motions of the two encapsulated H2O molecules. Both H2O and C60 moieties are treated as rigid and the cage-cage geometry is taken to be fixed. We consider the TR eigenstates of H2O@C60 monomers in the dimer to be coupled by the electric dipole-dipole interaction between water moieties and develop expressions for computing the matrix elements of that interaction in a dimer basis composed of products of monomer 6D TR eigenstates reported by us recently [P. M. Felker and Z. Bačić, J. Chem. Phys. 144, 201101 (2016)]. We use these expressions to compute TR Hamiltonian matrices of H2O@C60 dimer for two values of the water dipole moment and for various dimer geometries. 12D TR eigenstates of the dimer are then obtained by filter diagonalization. The results reveal two classes of eigenstates, distinguished by the leading order (first or second) at which dipole-dipole coupling contributes to them. The two types of eigenstates differ in the general magnitude of their dipole-induced energy shifts and in the dependence of those shifts on the value of the water dipole moment and on the distance between the H2O@C60 monomers. The dimer results are also found to be markedly insensitive to any change in the orientations of the C60 cages. Finally, the results lend some support for the interpretation that electric dipole-dipole coupling is at least partially responsible for the apparent reduced-symmetry environment experienced by H2O in the powder samples of H2O@C60 [K. S. K. Goh et al., Phys. Chem. Chem. Phys. 16, 21330 (2014)], but only if the water dipole is taken to have a magnitude close to that of free water. The methodology developed in the paper is transferable directly to the calculation of TR eigenstates of larger H2O@C60 assemblies, that will be required for more extensive modeling of crystalline H2O@C60.

Synthesis of C70‐Based Fluorophores through Sequential Functionalization to Form Isomerically Pure Multiadducts

AbstractSelective addition to the C70 cage divides its π‐conjugated system into various smaller π‐conjugated systems with enhanced fluorescent properties. Key reactions include chlorination, methoxylation, ozonation, and Bingel or Bingel–Hirsch reactions. The maximum emission wavelength of the C70 multiadducts ranges from 450 to 655 nm. Among the C70 multiadducts, C70(OMe)8(C(COOEt)2)3 showed the highest quantum yield (ΦF=0.18) and the largest Δ[λmax(emission)− λmax(absorption)] (402 nm), with maximum emission at 655 nm.

Synthesis of C70 -Based Fluorophores through Sequential Functionalization to Form Isomerically Pure Multiadducts.

Selective addition to the C70 cage divides its π-conjugated system into various smaller π-conjugated systems with enhanced fluorescent properties. Key reactions include chlorination, methoxylation, ozonation, and Bingel or Bingel-Hirsch reactions. The maximum emission wavelength of the C70 multiadducts ranges from 450 to 655 nm. Among the C70 multiadducts, C70 (OMe)8 (C(COOEt)2 )3 showed the highest quantum yield (ΦF =0.18) and the largest Δ[λmax (emission)- λmax (absorption)] (402 nm), with maximum emission at 655 nm.

Mononuclear Clusterfullerene Single‐Molecule Magnet Containing Strained Fused‐Pentagons Stabilized by a Nearly Linear Metal Cyanide Cluster

AbstractFused‐pentagons results in an increase of local steric strain according to the isolated pentagon rule (IPR), and for all reported non‐IPR clusterfullerenes multiple (two or three) metals are required to stabilize the strained fused‐pentagons, making it difficult to access the single‐atom properties. Herein, we report the syntheses and isolations of novel non‐IPR mononuclear clusterfullerenes MNC@C76 (M=Tb, Y), in which one pair of strained fused‐pentagon is stabilized by a mononuclear cluster. The molecular structures of MNC@C76 (M=Tb, Y) were determined unambiguously by single‐crystal X‐ray diffraction, featuring a non‐IPR C2v(19138)‐C76 cage entrapping a nearly linear MNC cluster, which is remarkably different from the triangular MNC cluster within the reported analogous clusterfullerenes based on IPR‐obeying C82 cages. The TbNC@C76 molecule is found to be a field‐induced single‐molecule magnet (SMM).

Mononuclear Clusterfullerene Single-Molecule Magnet Containing Strained Fused-Pentagons Stabilized by a Nearly Linear Metal Cyanide Cluster.

Fused‐pentagons results in an increase of local steric strain according to the isolated pentagon rule (IPR), and for all reported non‐IPR clusterfullerenes multiple (two or three) metals are required to stabilize the strained fused‐pentagons, making it difficult to access the single‐atom properties. Herein, we report the syntheses and isolations of novel non‐IPR mononuclear clusterfullerenes MNC@C76 (M=Tb, Y), in which one pair of strained fused‐pentagon is stabilized by a mononuclear cluster. The molecular structures of MNC@C76 (M=Tb, Y) were determined unambiguously by single‐crystal X‐ray diffraction, featuring a non‐IPR C 2v(19138)‐C76 cage entrapping a nearly linear MNC cluster, which is remarkably different from the triangular MNC cluster within the reported analogous clusterfullerenes based on IPR‐obeying C82 cages. The TbNC@C76 molecule is found to be a field‐induced single‐molecule magnet (SMM).

Chemical shielding of doped nitrogen on C20 cage and bowl fullerenes

The C20 (cage), C20 (bowl), C20H10 (bowl) fullerene structures and their nitrogen doped derivatives such as C20NH (cage), C20NH (bowl), C20H10N (bowl), C20H10NH (bowl) are fully optimized at the MPW1PW91/6-31G level of theory. The natural atomic charge comparison shows that in C20H10N (bowl), the nitrogen atom with about–0.58 has a more negative charge with respect to other nitrogen doped structures. The nuclear magnetic resonance chemical shielding is evaluated for nitrogen doped structures and the neighbors connected to nitrogen, C6, and C7 atoms. The nitrogen atom doped on carbon sites of C20H10N (bowl) has the largest shielding isotropic shifts to the upper field (–203.58 ppm). This means that the electron density around nitrogen in the C20H10N (bowl) structure is higher. Interestingly, there is a significant correlation between the charges and σiso values of nitrogen and carbon atoms (C6 and C7). Namely, as the charge becomes more negative, σiso shifts to the upper field. It is predicted that nitrogen doped C20H10N (bowl) with the maximum electron density adopts this structure for electrophilic reactions.

Computational Comparison of the Water-Dimer Encapsulations into D2(22)-C84 and D2d(23)-C84

The water dimer encapsulations into D2(22)-C84 and D2d(23)-C84 fullerenes are evaluated. The encapsulation energy is computed at the M06-2X/6-31++G** level and it is found that the energy gain upon encapsulation into the D2(22)-C84 and D2d(23)-C84 cages is −17.37 and −15.48 kcal/mol, respectively. Encapsulation equilibrium constants are computed using partitions functions based on the M06-2X/6-31++G** molecular data. The yield for (H2O)2@D2(22)-C84 is higher than for (H2O)2@D2d(23)-C84, however, the yield ratio decreases with increasing temperature and for high temperatures is close to 2:1. The M06-2X/6-31++G** computed rotational constants are presented for a possible use in detection of the water-dimer endohedrals by rotational spectroscopy in laboratory or interstellar space.

Unusual spin-polarized electron state in fullerene induced by carbon adatom defect.

First-principles calculations show that a carbon adatom defect at the Def[5, 6] site on the surface of C60 can produce a more stable spin-polarized singlet electronic state instead of a magnetic triplet state. This is clearly different from the cases of graphene and nanotubes. The mechanism results from the electron population of the adatom, which produces antiferromagnetic coupling around the C60 cage and the adatom itself. Our calculations show the same phenomenon occurs in other IPR fullerenes, such as C70 and C80. These findings extend the understanding of the magnetic origin of pure carbon structures and are valuable for research related to the spin polarization of carbon systems.

Synthesis, the electronic properties and efficient photoinduced electron transfer of new pyrrolidine[60]fullerene- and isoxazoline[60]fullerene-BODIPY dyads: nitrile oxide cycloaddition under mild conditions using PIFA

The first synthesis of fulleroisoxazoline-BODIPY whose electron-accepting ability of the C60 cage is better than its fulleropyrrolidine-BODIPY counterpart.

Doped fullerene as a metal-free electrocatalyst for oxygen reduction reaction: A first-principles study

The heteroatom-doped fullerene is systematically studied as an electrocatalyst for oxygen reduction reaction (ORR) on the cathode of fuel cells under the alkaline and acid conditions. Nitrogen-doped C60, i.e. C59N, can facilitate the ORR process and it is a promising candidate for efficient ORR electrocatalysts. The intrinsic C60 also possesses a high catalytic activity, which is different from graphene and is probably attributed to the curvature or pentagon defect of fullerene. We deduce that the curvature and pentagon defect are important factors to tune the catalytic ability. The fitted activity volcano diagram shows that the best achievable ORR activity of the heteroatom-doped fullerene, in the thermodynamic viewpoint, appears at ΔG*OH = 0.25 eV, which could be realized by dual or three-element-doping of C60 cage. The estimated standard equilibrium potential values are −0.52 and 0.25 V in alkaline and acid medium, respectively. Since the catalytic activity of the doped fullerenes depends on their IP and Egap, here we provide a simple and easy method, by measuring the IP and Egap, to roughly evaluate the catalytic ability of designed catalysts. This is vital to guide the design of new ORR catalysts with high catalytic activity and durability.

Co(I)-Mediated Removal of Addends on the C60 Cage and Formation of the Monovalent Cobalt Complex CpCo(CO)(η2-C60).

The removal of addends on the fullerene C60 cage plays an important role in the final stage for synthesizing endohedral fullerenes by the molecular surgery method. We developed a cobalt-mediated reaction to regenerate C60 from N-substituted C60 derivatives (aziridinofullerene and azafulleroid). In these reactions, we found the formation of a green monovalent-cobalt complex of C60, and its structure was unambiguously determined by X-ray analysis. The characteristic electronic structure of this cobalt complex was studied by IR and UV-vis absorption spectroscopy and electrochemical analyses.

The Ellenbogen's "Matter as Software" Concept for Quantum Computer Implementation: IV. The X@C60 Molecular Building Blocks (MBBs) and Computing System Lifetime Estimation

The problem of approximate lifetimes of individual X@C60 MBBs and tip-based nanofabricated quantum computing device systems is discussed under the conservative assumption of single-point failure. A single chemical transformation of the C60 cage into high-energy opened o-C60 isomer which forms the communication canal for the low energy transfer of an X atom from X@C60 MBB to the outside environment was studied. According to the PM7 method, the energy of o-C60 isomer is about 2.47 eV higher than that of C60 in the ground state. The estimated activation barrier between C60 and o-C60 isomer lies at 2.48 eV above the ground state of C60. A search for an individual activation barrier of the guest X atom was performed for the elements ranging between H and Bi, excluding Tc and lanthanides. Four X elements (Ru, Rh, Pd and Os) have been excluded from the available set of X@C60 MBBs because of their tendency to form stable insertion products with the wall of C60 cage.

Piperazine Functionalization of C70 for Incorporation into Supramolecular Assemblies

The photochemical reaction of piperazine with C70 produces a mono-adduct (N(CH2 CH2 )2 NC70 ) in high yield (67 %) along with three bis-adducts. These piperazine adducts can combine with various Lewis acids to form crystalline supramolecular aggregates suitable for X-ray diffraction. The structure of the mono-adduct was determined from examination of the adduct I2 N(CH2 CH2 )2 NI2 C70 that was formed by reaction of N(CH2 CH2 )2 NC70 with I2 . Crystals of polymeric {Rh2 (O2 CCF3 )4 N(CH2 CH2 )2 NC70 }n ⋅nC6 H6 that formed from reaction of the mono-adduct with Rh2 (O2 CCF3 )4 contain a sinusoidal strand of alternating molecules of N(CH2 CH2 )2 NC70 and Rh2 (O2 CCF3 )4 connected through Rh-N bonds. Silver nitrate reacts with N(CH2 CH2 )2 NC70 to form black crystals of {(Ag(NO3 ))4 (N(CH2 CH2 )2 NC70 )4 }n ⋅7nCH2 Cl2 that contain parallel, nearly linear chains of alternating (N(CH2 CH2 )2 NC70 molecules and silver ions. Four of these {Ag(NO3 )N(CH2 CH2 )2 NC70 }n chains adopt a structure that resembles a columnar micelle with the ionic silver nitrate portion in the center and the nearly non-polar C70 cages encircling that core. Of the three bis-adducts, one was definitively identified through crystallization in the presence of I2 as 12 {N(CH2 CH2 )2 N}2 C70 with addends on opposite poles of the C70 cage and a structure with C2v symmetry. In 12 {I2 N(CH2 CH2 )2 N}2 C70 , individual 12 {I2 N(CH2 CH2 )2 N}2 C70 units are further connected by secondary I2⋅⋅⋅N2 interactions to form chains that occur in layers within the crystal. Halogen bond formation between a Lewis base such as a tertiary amine and I2 is suggested as a method to produce ordered crystals with complex supramolecular structures from substances that are otherwise difficult to crystallize.

Triangular Monometallic Cyanide Cluster Entrapped in Carbon Cage with Geometry-Dependent Molecular Magnetism.

Clusterfullerenes are capable of entrapping a variety of metal clusters within carbon cage, for which the entrapped metal cluster generally keeps its geometric structure (e.g., bond distance and angle) upon changing the isomeric structure of fullerene cage, and whether the properties of the entrapped metal cluster is geometry-dependent remains unclear. Herein we report an unusual triangular monometallic cluster entrapped in fullerene cage by isolating several novel terbium cyanide clusterfullerenes (TbNC@C82) with different cage isomeric structures. Upon varying the isomeric structure of C82 cage from C2(5) to Cs(6) and to C2v(9), the entrapped triangular TbNC cluster exhibits significant distortions as evidenced by the changes of Tb-C(N) and C-N bond distances and variation of the Tb-C(N)-N(C) angle by up to 20°, revealing that the geometric structure of the entrapped triangular TbNC cluster is variable. All three TbNC@C82 molecules are found to be single-ion magnets, and the change of the geometric structure of TbNC cluster directly leads to the alternation of the magnetic relaxation time of the corresponding TbNC@C82 clusterfullerene.

The Unanticipated Dimerization of Ce@C2v (9)-C82 upon Co-crystallization with Ni(octaethylporphyrin) and Comparison with Monomeric M@C2v (9)-C82 (M = La, Sc, and Y).

We report that Ce@C2v (9)-C82 forms a centrosymmetric dimer when co-crystallized with Ni(OEP) (OEP = octaethylporphyrin dianion). The crystal structure of {Ce@C2v (9)-C82 }2 ⋅2[Ni(OEP)]⋅4 C6 H6 shows that a new C-C bond with a bond length of 1.605(5) Å connects the two cages. The high spin density of the singly occupied molecularorbital (SOMO) on the cage and the pyramidalization of the cage are factors that favor dimerization. In contrast, the treatment of Ni(OEP) with M@C2v (9)-C82 (M = La, Sc, and Y) results in crystallization of monomeric endohedral fullerenes. A systematic comparison of the X-ray structures of M@C2v (9)-C82 (M = Sc, Y, La, Ce, Gd, Yb, and Sm) reveals that the major metal site in each case is located at an off-center position adjacent to a hexagonal ring along the C2 axis of the C2v (9)-C82 cage. DFT calculations at the M06-2X level revealed that the positions of the metal centers in these metallofullerenes M@C2v (9)-C82 (M = Sc, Y, and Ce), as determined by single-crystal X-ray structure studies, correspond to an energy minimum for each compound.

Linear and nonlinear optical properties of M@C59X (M = Li, Na and X = B, N) cage

By applying the density functional theory (DFT) combined with sum-over-orbital (SOO) approach, the static and frequency dependent nonlinear optical (NLO) properties of the C60 and M@C59X cages have been studied. The NLO properties of the C60 cage have been investigated by considering effects of substitution of one B or N atom at one of C sites and Li or Na atoms encapsulation in the C60 cage (SED). The numerical results show that the polarizabilities and second hyperpolarizabilities values of the C60 cage can greatly vary with respect to SED type. As, highest peak value of second hyperpolarizabilities for Na@C59N is about 34, 1.8 and 1.1 times larger than that of the C60, Li@C59X and Na@C59B cages, respectively. These results can be important to experimentalists for designing new NLO materials with large NLO responses.

Water Entrapped inside Fullerene Cages: A Potential Probe for Evaluation of Bond Polarization.

The concept of the bond polarization is a useful tool to understand chemical reactions and fundamental properties of compounds. However, experimental considerations are limited owing to its difficulty of reliable description. We demonstrated that geometrically isolated H2 O inside the cage of fullerene C60 is a possible probe to evaluate the polarization degree of covalent bonds C(C60 )-X (X=heteroatom) on the C60 cage. The 1 H NMR relaxation times of entrapped H2 O have been systematically measured at variable temperatures for H2 O@C60 X (X=CR2 , NR, O, and O2 ). The results followed in the order of electronegativities of C (2.55), N (3.04), and O (3.44), indicating that entrapped H2 O can sensitively respond to the degree of the bond polarization.

Water Entrapped inside Fullerene Cages: A Potential Probe for Evaluation of Bond Polarization

AbstractThe concept of the bond polarization is a useful tool to understand chemical reactions and fundamental properties of compounds. However, experimental considerations are limited owing to its difficulty of reliable description. We demonstrated that geometrically isolated H2O inside the cage of fullerene C60 is a possible probe to evaluate the polarization degree of covalent bonds C(C60)−X (X=heteroatom) on the C60 cage. The 1H NMR relaxation times of entrapped H2O have been systematically measured at variable temperatures for H2O@C60X (X=CR2, NR, O, and O2). The results followed in the order of electronegativities of C (2.55), N (3.04), and O (3.44), indicating that entrapped H2O can sensitively respond to the degree of the bond polarization.

Analysis of fullerenes in soils samples collected in The Netherlands

Fullerenes are carbon based nanoparticles that may enter the environment as a consequence of both natural processes and human activities. Although little is known about the presence of these chemicals in the environment, recent studies suggested that soil may act as a sink. The aim of the present work was to investigate the presence of fullerenes in soils collected in The Netherlands. Samples (n = 91) were taken from 6 locations and analyzed using a new developed LC-QTOF-MS method. The locations included highly trafficked and industrialized as well as urban and natural areas. In general, C60 was the most abundant fullerene found in the environment, detected in almost a half of the samples and at concentrations in the range of ng/kg. Other fullerenes such as C70 and an unknown structure containing a C60 cage were detected to a lower extent. The highest concentrations were found in the proximity of combustion sites such as a coal power plant and an incinerator, suggesting that the nanoparticles were unintentionally produced during combustions processes and reached the soil through atmospheric deposition. Consistent with other recent studies, these results show that fullerenes are widely present in the environment and that the main route for their entrance may be due to human activities. These data will be helpful in the understanding of the distribution of fullerenes in the environment and for the study of their behavior and fate in soil.

Tunneling Motion and Antiferroelectric Ordering of Lithium Cations Trapped inside Carbon Cages

Dielectric and X-ray diffraction measurements of [Li@C60](PF6) single crystals reveal the motion of the Li+ cations inside the C60 cages at low temperature. An increase in the dielectric permittivity below 100 K is consistent with a combined tunneling and hopping motion of the Li+ cation between two positions inside the C60 cage. A phase transition accompanied by a decrease in the dielectric permittivity at TC = 24 K is explained by an antiferroelectric ordering of the Li+ cations. The Li+ ordering is caused by interactions among electric dipole moments formed between the Li+ cations inside and the PF6− anions outside the C60 cages. The electric dipole moments that are switched by the Li+ tunneling and interact with each other are potential qubits in a quantum computer using electric dipole moments.