Central Pentagon Research Articles

Reaction of Tl+ with corannulene: Experimental and theoretical study

The interaction of Tl+ cation with corannulene was investigated by using electrospray ionization mass spectrometry (ESI-MS). It was found that the thallium cation Tl+ forms with corannulene (C20H10) two cationic complexes [Tl(C20H10)]+ and [Tl(C20H10)2]+. Quantum chemical calculations proceed by density functional theory with two different functionals (B3LYP and M06-D3) provided the most probable structures of these complexes. In the energetically most favored conformation of [Tl(C20H10)]+ complex, the Tl+ cation lies on the apex of pyramid which base is formed by the central pentagon of the convexly oriented corannulene molecule. In the [Tl(C20H10)2]+ complex the “central” cation Tl+ is situated between two molecules of the corannulene ligand. Both ligand molecules are convex to the Tl+ cation. The interaction energies, E(int), of the considered cation-π complexes [Tl(C20H10)]+ and [Tl(C20H10)2]+ were calculated to be −121.75 and −176.98 kJ/mol, respectively.

Nitric oxide oxidation on warped nanographene (C80H30): a DFT study

The possible use of the recently synthesized warped nanographene C80H30 for NO oxidation by O2 molecule has been investigated using density functional theory. The reaction starts with the adsorption and dissociation of O2 molecule on the central pentagon of C80H30 with the activation energies of 24.2–26.6 kcal/mol depending on the active sites. Then, the dissociated O atoms readily oxidize NO to NO2 twice. The first NO oxidation occurs with barrierless, while the second NO oxidation requires a small energy barrier of 16.0 kcal/mol. The low activation energy barrier pathway indicates high catalytic activity of this nanographene for NO oxidation. Charge analysis reveals that such high catalytic activity of nanographene is attributed to the charge transfer from the saddle-shaped C80H30 to the dissociated O atoms which makes it reactive to NO molecule. Desorption of NO2 product, which is the rate-limiting step of NO oxidation in some catalysts, is easily occurred in this nanographene (less than 2 kcal/mol), indicating the prevention of catalyst poisoning. This study suggests that C80H30 nanographene is a promising catalyst for NO removal in ambient condition.

ChemInform Abstract: Buckybowls: Corannulene and Its Derivatives.

Corannulene, a kind of bowl like polycyclic aromatic hydrocarbon (PAH), whose molecule is composed of a central pentagon and five closely adjacent hexagons on the pentagon's five sides, has received great scientific interest among research groups. In this review, the syntheses, characteristic molecule structure and properties of corannulene are clarified, as well as its derivatives with different substituted groups, fused derivatives, metal complex, and derivatives for host guest chemistry. On the basis of reviewing the applications and properties of corannulene together with its derivatives, the potential applications in hydrogen storage and lithium storage were highlighted and prospected.

Buckybowls: Corannulene and Its Derivatives.

Corannulene, a kind of bowl like polycyclic aromatic hydrocarbon (PAH), whose molecule is composed of a central pentagon and five closely adjacent hexagons on the pentagon's five sides, has received great scientific interest among research groups. In this review, the syntheses, characteristic molecule structure and properties of corannulene are clarified, as well as its derivatives with different substituted groups, fused derivatives, metal complex, and derivatives for host guest chemistry. On the basis of reviewing the applications and properties of corannulene together with its derivatives, the potential applications in hydrogen storage and lithium storage were highlighted and prospected.

Preparation of Azafullerene C59NR5 and Fullerene Derivative C60NAr5 with a Pyridine Moiety on the Cage Skeleton.

[60]Fullerene hexaadducts C60R5Cl (R = OMe or Ar) reacted with hydroxylamine to form C60R5(NHOH) with the hydroxylamino group attached on the central pentagon as in the starting material. Further reactions including treatment with PCl5 and basic alumina led to the insertion of the nitrogen atom into the fullerene cage skeleton and decarbonylation to form azafullerenes C59N(H)(OMe)4 and C59N(OMe)5. The fullerene derivatives C59N(CO)R5 and C60NAr5 with a pyridinone and a pyridine moiety on the cage skeleton, respectively, were also synthesized starting from the hydroxylamine adducts.

Unusual multistep reaction of C70Cl10 with thiols producing C70[SR]5H

We report a reaction of the chlorofullerene C70Cl10 with thiols producing C70[SR]5H with all organic addends attached around one central pentagon at the pole of the C70 cage. This reaction was shown to proceed via a complicated radical pathway, presumably involving addition, substitution, rearrangement, and/or elimination steps. The obtained C70[SR]5H products were shown to be very unstable and undergo quantitative decomposition to pristine C70, RSSR, and RSH at elevated temperatures (e.g., 50°C). Quantum chemical calculations and NMR spectroscopy data showed that cleavage of organic addends from the fullerene cage could be induced by solvation effects in solution.

Magnetic and structural properties of single 3d transition metals adsorbed on corannulene: A density functional theory study

We have obtained magnetic properties of single 3d transition metal atoms (from Sc to Ni) adsorbed on both concave and convex surfaces of corannulene. Binding energies, spin and orbital magnetic moments, and charge transfer between added transition metal and corannulene were determined. We have done our calculations in the framework of relativistic density functional theory in the regime of generalized gradient approximation. Our calculations show that TM atoms added on corannulene convex surface except Co and Ni are mostly stable on hollow site of hexagon rings, whereas for concave surface all TM atoms are stable on hollow sites of central pentagon ring except Sc where it is stable on C–C bond of pentagon ring. Binding energy calculations show that most TM atoms prefer to bind on the convex surface of corannulene. All structures are magnetized except Ni-corannulene structure.

Preparation of a 12-Membered Open-Cage Fullerendione through Silane/Borane-Promoted Formation of Ketal Moieties and Oxidation of a Vicinal Fullerendiol

[60]Fullerene mixed peroxide C(60) (OH)(Cl)(OOtBu) reacts with PhMe(2)SiH/B(C(6)F(5))(3) to give oxahomofullerene. Mechanistic investigation indicates that the hydroxyl group in the central pentagon ring is essential to convert the tert-butylperoxo group into a ketal moiety. Migration of the silyl group and transformation of the siloxy group into a phenyl group are observed in the deprotection of the fullerene bound siloxy group. A 12-membered open-cage fullerendione was obtained through oxidation of a [6,6]-fullerendiol. This orifice could be closed to form ketal/hemiketal moieties by BF(3)-catalyzed reaction with methanol. All of the new fullerene derivatives were characterized by spectroscopic data, and structure of the open-cage fullerendione was also confirmed by single-crystal X-ray analysis.

Synthesis and Reactivity of 2H-Pyran Moiety in [60]Fullerene Cage Skeleton

The cyclopentadienyl type hexa-adduct C(60)(OOtBu)(6) 1 is readily converted into 2H-pyran containing fullerene derivative C(60)(O)(OOH)(OOtBu)(5) 2 in the presence of NaHCO(3) and hydroquinone. In the process, O-O bond of the tert-butylperoxo group on the central pentagon is cleaved, and the fullerene-bound oxygen radical inserts into a 5,6-junction to form the 2H-pyran moiety. Further reactions of 2 led to open-cage fullerenes with a nine-membered orifice and also both 3,4-dihydro-2H-pyran and 3,6-dihydro-2H-pyran containing fullerene derivatives. Mechanisms are proposed involving intramolecular S(N)2' and aza-Michael addition and ketal formation processes.

Defect motifs for spherical topologies

Putative global minima for the Thomson problem of $N$ charges on a sphere are located for selected sizes in the range $N\ensuremath{\le}4352$. For small sizes most global minima simply exhibit 12 disclinations. However, around $N=400$ extended dislocations are common, where a heptagon lies between two pentagons in the Voronoi representation. At larger sizes around $N=1000$ twinned grain boundaries are favorable and then between about $N=1000$ and 2000 ``rosette'' defects appear, containing a central pentagon surrounded by five heptagons alternating with five additional pentagons in the Voronoi representation. Structures with 12 rosettes and $I$ point group symmetry are particularly low in energy for $N=1632$ and 1902. Above $N=2000$ the lowest minima located generally contain irregular grain boundaries, sometimes with a few rosette defects. Face dual carbon clusters corresponding to ${I}_{h}$ local minima at $N=432$ and 582 are characterized as local minima for ${\text{C}}_{860}$ and ${\text{C}}_{1160}$.

Theoretical investigation of nitrogen disubstituted corannulenes

The effect of nitrogen substitution on corannulene has been investigated employing the PBE density functional and the 6-31G* basis set. We have replaced two carbon atoms by 2 nitrogen atoms. Among the 22 isomers investigated we have found that the most stable C 18N 2H 20 isomer, 1 has two nitrogen atoms on the same six membered ring, in para positions. One of the nitrogen atoms in located at the rim of corannulene and the other is at the hub of corannulene. The later result is in excellent agreement with the predicted stability of C 58N 2 heterofullerenes. Thus, it seems that there is a clear correlation between the stability of substituted heterofullerenes and heterobuckybowls. The triplet state of isomer 1 is 18 kcal/mol less stable than the singlet state. The second most stable isomer, 2, also have one nitrogen at the rim and another at the hub, it less stable than isomer 1 by 6.2 kcal/mol. However, isomers 2–5 are extremely close in energetic terms. The IR spectra of the most stable isomers, NMR chemical shifts and NICS have been determined. The results indicate that the aromaticity of isomer 1 diminished from that observed in corannulene. Isomer 1 has small aromatic character in the central pentagon and two hexagons; the antiaromatic character is seen for the remaining 3 hexagons. The later results are in contrast with the observed for corannulene, which has aromatic character in the hexagons and antiaromatic on the pentagon. The HOMO–LUMO gap of isomer 1 is 1.23 eV, suggesting reasonable kinetic stability, although it is more than a 50% smaller than that of corannulene 3.03 eV. As by product we have investigated the properties of 1,2-diazacorannulene, a parent compound of 1,2-diazadibenzo[ d,m]corannulene whose synthesis was not reached in a recent work.

Boomerang‐Type Substitution Reaction: Reactivity of Fullerene Epoxides and a Halofullerenol

The C(s)-symmetric fullerene chlorohydrin C60(Cl)(OH)(OOtBu)4 reacts with 4-dimethylaminopyridine (DMAP) and 1,4-diazabicyclo[2.2.2]octane (DABCO) to yield two isomers with the formula C60(O)(OOtBu)4 in good yields. These isomers differ with respect to the location of the epoxy functionality. The one from DMAP is C(s) symmetric, whereas that from DABCO is C1 symmetric with the epoxy group on the central pentagon. Two different mechanisms are proposed to explain the chemoselectivity of these reactions. The reaction with DMAP involves single-electron transfer as the key step; DMAP acts as the electron donor. A combination of an oxygen-atom shift and S(N)2'' processes (boomerang substitution) are responsible for the formation of isomer with DACBO. Various related reactions support the proposed mechanisms. The structures of new fullerene derivatives were determined by spectroscopy, single-crystal X-ray analysis, and chemical correlation experiments.

Field electron emission images of multi-walled carbon nanotubes

Field electron emission microscope images from multi-walled carbon nanotubes can typically be characterized by the presence of five pentagons surrounding a sixth central pentagon. The observations of bright line centered interference patterns between adjacent pentagons in the field electron emission microscope images of multi-walled carbon nanotubes have been reported in the literature. We have observed a shift from bright to dark line centered interference patterns and associated this with the presence of surface adsorption. In order to identify the origin of the contaminant, multi-walled carbon nanotubes were dosed with H 2, H 2O, CO and O 2 and then imaged in the field electron emission microscope. Only the samples exposed to O 2 showed a shift from a bright line centered pattern between adjacent pentagons of a clean surface to a dark line centered pattern when one pentagon was contaminated or a bright line centered pattern when both adjacent pentagons become contaminated. The results of the experimental studies and the modeling of the changes in the field emission pattern as phase shifts in the wave function of the tunneling electrons due to modifications in the surface work function are presented.

Amination of [60]Fullerene by Ammonia and by Primary and Secondary Aliphatic Amines—Preparation of Amino[60]fullerene Peroxides

Ammonia and aliphatic amines react readily in the oxygen-rich regions of the Cs symmetric fullerene peroxides C60(O)(OOtBu)4 (1) and C60(OH)(Br)(OOtBu)4 (2 c). Michael addition-type hydroamination of the 1,4-diene moiety on the central skew-pentagon was observed when 1 was treated with ammonia or with nonbulky primary amines, while sterically demanding primary amines opened the epoxy moiety to form vicinal aminohydroxy fullerene compounds with the amino group on the central pentagon. In 2 c the bromo group was replaced under similar conditions by ammonia and primary amines. Cyclic secondary amines showed different reaction patterns, forming hydrogenation products or aminoketal-fullerenes when treated with 1 and 2 c, respectively. Single-electron transfer (SET) is the key step in all the proposed mechanisms. The compounds were characterized by their spectroscopic data, and in addition, three single-crystal X-ray structures were obtained.

DFT Study of Structure and Binding Energies of Fe−Corannulene Complex

Density functional theory (DFT) based theoretical calculations are performed to identify the ground-state geometries, the spin multiplicities, and the relevant energetics of neutral and positively charged Fe-corannulene complexes. Our calculations show that the on-top site of the six-membered ring (eta(6)) of corannulene molecule is the most preferred binding site for both Fe atom and Fe(+) ion. The electrostatic potential (ESP) surface picture is employed to explain the preference of the eta(6)- over the eta(5)-binding site (on-top site of central pentagon) of corannulene. Though in both neutral and cationic species the eta(6)-site is the most preferred binding site, the ground-state geometries of these complexes are different. The Fe(+) cation prefers to bind to the convex face of the corannulene, whereas the neutral Fe atom prefers slightly the concave to the convex face. The ionization-induced structural changes are reflected in the large energy difference between the vertical and adiabatic ionization potential values. We also show that the dissociation of Fe(+)-corannulene complex to corannulene + Fe(+) is just as likely as that to Fe + (corannulene)(+).

Non-empirical calculation of electronic states of impurity polygon in carbon sheet: 1, 2 and 3 pentagons

Electronic states of 1, 2 and 3 impurity pentagons in carbon sheet are calculated by the DV-Xα-LCAO method. The C atoms near the tail end are negatively charged and other C atoms are almost neutral. Both the occupied and unoccupied orbitals near the HOMO have high charge density around the central pentagon and tail end. This well reproduces the scanning tunneling microscopy images of 1 impurity pentagon. Furthermore, electronic states of 2 and 3 impurity pentagons in carbon sheet resemble those of fullerene molecule C60 adsorbed on Si(001)2×1 and Si(111)7×7 surfaces, respectively.

C 70 Ions in Chains

CHEMISTRY Fullerenes such as C60 and C70 are easily reduced and can accept a large number of negative charges. Dimeric, oligomeric, and polymeric (C60 n −) x ions have been studied, but the nature of the bonds linking the C60 units is not known precisely because no structural study has yet resolved all of the carbon positions; few studies of (C70 n −) x ions have been reported. Brumm et al . have synthesized a linear polymeric C702− species as a barium salt and have localized and refined all of the carbon atoms (and thus the bond lengths) of the fullerene cage. The C70 units form zigzagging chains that are connected by bonds between carbon atoms in the five-membered rings at the “ends” of the molecule (these are the rings through which the fivefold rotational axis runs). In a two-dimensional representation (Schlegel projection) of the C70 molecule, the central pentagon represents the C70 face closest to the reader, and the outermost pentagon represents the opposing face on the far side of molecule. The bond lengths indicate that the negative charges are not localized on specific carbon atoms. — JU Angew. Chem. Int. Ed. 40 , 2069 (2001).

Non-Empirical Calculation of Electronic States of Impurity Polygon in Carbon Sheet: Pentagon

Electronic states of the impurity pentagon in carbon sheet are calculated by the DV-Xα-LCAO method. The neighboring C atom of the central pentagon is negatively charged and other C atoms are almost neutral. The electric field for a negative (positive) sample bias induces the electron transfer from the tail-end (central pentagon) C atoms of carbon sheet to the central pentagon (tail-end) C atoms. Both the occupied orbitals near the HOMO for the negative sample bias and the unoccupied orbitals for the positive sample bias have high charge density around the central pentagon. This well reproduces the scanning tunneling microscopy images.

Application of symmetry operations for construction of quasiperiodic structures in a plane

A method is proposed for constructing a quasiperiodic structure of symmetry elements — regular pentagons and five-pointed stars — in a plane. The growth of the structure is determined by the action of the symmetry operations, whose effect is not completely identical to that of similar operations in classical crystallography. The tiling (“flower of pentagons”), consisting of a central pentagon and five side pentagons joined along the edges, is studied. The growth of this tiling is accompanied by the appearance of a “flower of stars” and by the formation of isolated pores in the form of rhombi. The relation between the obtained structure and Penrose tiling is examined, and it is noted that some vertices of the Penrose tiling coincide with all vertices of the polygons of the packing obtained.