Unusual pentagon and hexagon geometry of three isomers (no 1, 20, and 23) of fullerene C84

Three isomers 23 (D_2d), 1 (D₂), and 20 (T_d) of fullerene C₈₄ have been investigated by PM3, HF/6‐31G*, and DFT methods with B3LYP functional at the 6‐31G and 6‐31G* levels. In this article we reveal for the first time that some distortion of hexagon (pentagon), measured as its maximal dihedral angles, caused by local molecular strains may serve as a new criterion of stability of fullerenes with closed shell. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Multiple Pentafluorophenylation of 2,2,3,3,5,6,6‐Heptafluoro‐3,6‐dihydro‐2H‐1,4‐oxazine with an Organosilicon Reagent: NMR and DFT Structural Analysis of Oligo(perfluoroaryl) Compounds

The reagent Me₃Si(C₆F₅) was used for the preparation of a series of perfluorinated, pentafluorophenyl‐substituted 3,6‐dihydro‐2H‐1,4‐oxazines ( 2 – 8 ), which, otherwise, would be very difficult to synthesize. Multiple pentafluorophenylation occurred not only on the heterocyclic ring of the starting compound 1 (Scheme), but also in para position of the introduced C₆F₅ substituent(s) leading to compounds with one to three nonafluorobiphenyl (C₁₂F₉) substituents. While the tris(pentafluorophenyl)‐substituted compound 3 could be isolated as the sole product by stoichiometric control of the reagent, the higher‐substituted compounds 5 – 8 could only be obtained as mixtures. The structures of the oligo(perfluoroaryl) compounds were confirmed by ¹⁹F‐ and ¹³C‐NMR, MS, and/or X‐ray crystallography. DFT simulations of the ¹⁹F‐ and ¹³C‐NMR chemical shifts were performed at the B3LYP‐GIAO/6‐31++G(d,p) level for geometries optimized by the B3LYP/6‐31G(d) level, a technique that proved to be very useful to accomplish full NMR assignment of these complex products.     

[6,6]‐Open and [6,6]‐Closed Isomers of C70(CF2): Synthesis,Electrochemical and Quantum Chemical Investigation

Novel difluoromethylenated [70]fullerene derivatives, C₇₀(CF₂)_n (n=1–3), were obtained by the reaction of C₇₀ with sodium difluorochloroacetate. Two major products, isomeric C₇₀(CF₂) mono‐adducts with [6,6]‐open and [6,6]‐closed configurations, were isolated and their homofullerene and methanofullerene structures were reliably determined by a variety of methods that included X‐ray analysis and high‐level spectroscopic techniques. The [6,6]‐open isomer of C₇₀(CF₂) constitutes the first homofullerene example of a non‐hetero [70]fullerene derivative in which functionalisation involves the most reactive bond in the polar region of the cage. Voltammetric estimation of the electron affinity of the C₇₀(CF₂) isomers showed that it is substantially higher for the [6,6]‐open isomer (the 70‐electron π‐conjugated system is retained) than the [6,6]‐closed form, the latter being similar to the electron affinity of pristine C₇₀. In situ ESR spectroelectrochemical investigation of the C₇₀(CF₂) radical anions and DFT calculations of the hyperfine coupling constants provide evidence for the first example of an inter‐conversion between the [6,6]‐closed and [6,6]‐open forms of a cage‐modified fullerene driven by an electrochemical one‐electron transfer. Thus, [6,6]‐closed C₇₀(CF₂) constitutes an interesting example of a redox‐switchable fullerene derivative.     

C80, C86, C88: Semiempirical and ab initio SCF calculations

Three complete sets of the isolated-pentagon-rule fullerene isomers are considered—₈₀ (7 species), C₈₆ (19 species), and C₈₈ (35 species). The interisomeric separation energetics is essentially similar at semiempirical (AM1, SAM1) and ab initio (HF/STO-3G, HF/3-21G, HF/4-31G) levels. For the C₈₀ set, the HF/4-31G computations explain why the lowest-energy isomer is not experimentally observed. The computations also agree with observations on C₈₆ and C₈₈. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 529–535, 1997     

N,N‐Diethyl‐N′‐[(E)‐4‐pyridylmethylene]benzene‐1,4‐diamine: a combined X‐ray and density functional theory study

The crystal structure of the title compound, C₁₆H₁₉N₃, comprises neutral molecules of a dipolar Schiff base chromophore. A density functional theory (DFT) optimized structure at the B3LYP/6‐31G(d) level is compared with the molecular structure in the solid state. The compound crystallizes in the noncentrosymmetric space group Pna2₁ with a herring‐bone packing motif and is therefore a potential candidate for nonlinear optical effects in the bulk.     

C68 Fullerene Isomers,Anions, and their Metallofullerenes: Charge‐Stabilizing Different Isomers

The complete set of 6332 classical isomers of the fullerene C₆₈ as well as several non‐classical isomers is investigated by PM3, and the data for some of the more stable isomers are refined by the DFT‐based methods HCTH and B3LYP. C₂:0112 possesses the lowest energy of all the neutral isomers and it prevails in a wide range of temperatures. Among the fullerene ions modeled, C₆₈^2?, C₆₈^4? and C₆₈^6?, the isomers C₆₈^2?(C_s:0064), C₆₈^4?(C_2v:0008), and C₆₈^6?(D₃:0009) respectively, are predicted to be the most stable. This reveals that the pentagon adjacency penalty rule (PAPR) does not necessarily apply to the charged fullerene cages. The vertical electron affinities of the neutral C_s:0064, C_2v:0008, and D₃:0009 isomers are 3.41, 3.29, and 3.10 eV, respectively, suggesting that they are good electron acceptors. The predicted complexation energy, that is, the adiabatic binding energy between the cage and encapsulated cluster, of Sc₂C₂@C₆₈(C_2v:0008) is ?6.95 eV, thus greatly releasing the strain of its parent fullerene (C_2v:0008). Essentially, C₆₈ fullerene isomers are charge‐stabilized. Thus, inducing charge facilitates the isolation of the different isomers. Further investigations show that the steric effect of the encaged cluster should also be an important factor to stabilize the C₆₈ fullerenes effectively.     

Quantum chemical calculations of the molecular structures of hybrid amino acid derivatives of fullerene C60

The stereoselectivity of the formation of hybrid amino acid derivatives of fullerene (AADF) C₆₀ was studied. The energies of the model addition reactions C₆₀ + n C₂H₆ ? Me _n -C₆₀-Me _n (1) and C₆₀ + n EtNC₄H₇Me ? Et _n -C₆₀-(NC₄H₇Me) _n (2) (n = 1–3) were calculated by the DFT method B3LYP/6-31G*. The most stable products of reaction (1) are hexamethylated fullerene derivatives in which five Me groups are arranged in the form of a regular pentagon. Among the AADF obtained by reaction (2), 1,4-disubstituted fullerene isomers are most stable. The molecular structures of such isomers were calculated for six biologically active hybrid AADF; the solvent contact areas of these molecules were evaluated.     

Assigning the major isomers of fullerene C88 by theoretical 13C NMR spectra

The IPR isomers of fullerene C₈₈ have been studied using density functional theory. Structures of all C₈₈ isomers with non-zero HOMO–LUMO gaps were optimized at the B3LYP/STO-3G level. Those isomers having energies lower than 25 kcal/mol were subjected to geometry optimization using the 6-31G basis set. Isomer 17 has the lowest energy, followed by 7 and 33. All three isomers have large HOMO–LUMO gaps. ¹³C NMR chemical shifts were obtained employing the GIAO method. The comparison between predicted and measured NMR spectra strongly supports the observed C₈₈-1(C_s) as isomer 17, and isomers C₈₈-2(C₂) and C₈₈-3(C₂) as 7 and 33, respectively.     

Chemically modified fullerene derivatives as photosensitizers in photodynamic therapy: A first‐principles study

The first‐principles density functional theory (DFT) and its time‐dependent approach (TD‐DFT) are used to characterize the electronic structures and optical spectra properties of five chemically modified fullerenes. It is revealed that the metal fullerene derivatives possess not only stronger absorption bands in visible light regions than organically modified fullerene but also the large energy gaps (ΔE_S–T > 0.98 eV) between the singlet ground state and the triplet state, which imply their significant aspect of potential candidates as a photosensitizer. We have found that a new metal‐containing bisfullerene complexes (Pt(C₆₀)₂), with the extended conjugated π‐electrons, much degenerate orbitals and a uniform electrostatic potential surface, behave more pre‐eminent photosensitizing properties than other examined fullerene derivatives. © 2012 Wiley Periodicals, Inc.     

Synthesis,Structure, and Theoretical Study of Trifluoromethyl Derivatives of C84(22) Fullerene

Trifluoromethylation of higher fullerene mixtures with CF₃I was performed in ampoules at 400 to 420 and 550 to 560 °C. HPLC separation followed by crystal growth and X‐ray diffraction studies allowed the structure elucidation of nine CF₃ derivatives of D₂‐C₈₄ (isomer 22). Molecular structures of two isomers of C₈₄(22)(CF₃)₁₂, two isomers of C₈₄(22)(CF₃)₁₄, four isomers of C₈₄(22)(CF₃)₁₆, and one isomer of C₈₄(22)(CF₃)₂₀ were discussed in terms of their addition patterns and relative formation energies. DFT calculations were also used to predict the most stable molecular structures of lower CF₃ derivatives, C₈₄(22)(CF₃)_2–10. It was found that the addition of CF₃ groups to C₈₄(22) is governed by two rules: additions can only occur at para positions of C₆(CF₃)₂ hexagons and no additions can occur at triple‐hexagon‐junction positions on the fullerene cage.     

4‐(2,5‐Dioxo‐2,5‐dihydro‐1H‐pyrrol‐1‐yl)benzoic acid: X‐ray and DFT‐calculated structure

In the title compound, C₁₁H₇NO₄, there is a dihedral angle of 45.80 (7)° between the planes of the benzene and maleimide rings. The presence of O—H...O hydrogen bonding and weak C—H...O interactions allows the formation of R₃³(19) edge‐connected rings parallel to the (010) plane. Structural, spectroscopic and theoretical studies were carried out. Density functional theory (DFT) optimized structures at the B3LYP/6–311 G(d,p) and 6–31++G(d,p) levels are compared with the experimentally determined molecular structure in the solid state. Additional IR and UV theoretical studies allowed the presence of functional groups and the transition bands of the system to be identified.     

Chlorination‐Promoted Skeletal‐Cage Transformations of C88 Fullerene by C2 Losses and a CC Bond Rotation

High‐temperature chlorination of fullerene C₈₈ (isomer 33) with VCl₄ gives rise to skeletal transformations affording several nonclassical (NC) fullerene chlorides, C₈₆(NC1)Cl_24/26 and C₈₄(NC2)Cl₂₆, with one and two heptagons, respectively, in the carbon cages. The branched skeletal transformation including C₂ losses as well as a Stone–Wales rearrangement has been comprehensively characterized by the structure determination of two intermediates and three final chlorination products. Quantum‐chemical calculations demonstrate that the average energy of the C?Cl bond is significantly increased in chlorides of nonclassical fullerenes with a large number of chlorinated sites of pentagon–pentagon adjacency.     

Synthesis of New Porphyrin–Fullerene Dyads Capable of Forming Charge‐Separated States on a Microsecond Lifetime Scale

A series of covalently linked axially symmetric porphyrin–fullerene dyads with a rigid pyrrolo[3,4‐c]pyrrolic linker enabling a fixed and orthogonal arrangement of the chromophores has been synthesized and studied by means of transient absorption spectroscopy and cyclic voltammetry. The lifetime of the charge‐separated state has been found to depend on the substituents on the porphyrin core, reaching up to 4 μs for a species with meso‐(p‐MeOC₆H₄) substituents. The ground and excited electronic states of model compounds have been calculated at the DFT and TD‐DFT B3LYP(6‐31G(d)) levels of theory and analyzed with regard to the effect of the substituent on the stabilization of the charge‐separated state in the porphyrin–fullerene ensemble with a view to explaining the observed dependence.     

High‐Potential Perfluorinated Phthalocyanine–Fullerene Dyads for Generation of High‐Energy Charge‐Separated States: Formation and Photoinduced Electron‐Transfer Studies

High oxidation potential perfluorinated zinc phthalocyanines (ZnF_nPcs) are synthesised and their spectroscopic, redox, and light‐induced electron‐transfer properties investigated systematically by forming donor–acceptor dyads through metal–ligand axial coordination of fullerene (C₆₀) derivatives. Absorption and fluorescence spectral studies reveal efficient binding of the pyridine‐ (Py) and phenylimidazole‐functionalised fullerene (C₆₀Im) derivatives to the zinc centre of the F_nPcs. The determined binding constants, K, in o‐dichlorobenzene for the 1:1 complexes are in the order of 10⁴ to 10⁵ M ^?1; nearly an order of magnitude higher than that observed for the dyad formed from zinc phthalocyanine (ZnPc) lacking fluorine substituents. The geometry and electronic structure of the dyads are determined by using the B3LYP/6‐31G* method. The HOMO and LUMO levels are located on the Pc and C₆₀ entities, respectively; this suggests the formation of ZnF_nPc^.+–C₆₀Im^.? and ZnF_nPc^.+–C₆₀Py^.? (n=0, 8 or 16) intra‐supramolecular charge‐separated states during electron transfer. Electrochemical studies on the ZnPc–C₆₀ dyads enable accurate determination of their oxidation and reduction potentials and the energy of the charge‐separated states. The energy of the charge‐separated state for dyads composed of ZnF_nPc is higher than that of normal ZnPc–C₆₀ dyads and reveals their significance in harvesting higher amounts of light energy. Evidence for charge separation in the dyads is secured from femtosecond transient absorption studies in nonpolar toluene. Kinetic evaluation of the cation and anion radical ion peaks reveals ultrafast charge separation and charge recombination in dyads composed of perfluorinated phthalocyanine and fullerene; this implies their significance in solar‐energy harvesting and optoelectronic device building applications.     

Thermochemical properties for n‐propyl,iso‐propyl,and tert‐butyl nitroalkanes,alkyl nitrites,and their carbon‐centered radicals

Density functional theory (DFT) based calculations are performed on a series of alkyl nitrites and nitroalkanes representing large‐scale primary, secondary, and tertiary nitro compounds and their radicals resulting from the loss of their skeletal hydrogen atoms. Geometries, vibration frequencies, and thermochemical properties [S°(T) and C°_p(T) (10 K ? T ? 5000 K)] are calculated at the B3LYP/6‐31G(d,p) DFT level. Δ_fH°₂₉₈ values are from B3LYP/6‐31G(d,p), B3LYP/6‐31+G(2d,2p), and the composite CBS‐QB3 levels. Potential energy barriers for the internal rotations have been computed at the B3LYP/6‐31G(d,p) level of theory, and the lower barrier contributions are incorporated into entropy and heat capacity data. The standard enthalpies of formation at 298 K are evaluated using isodesmic reaction schemes with several work reactions for each species. Recommended values derived from the most stable conformers of respective nitro‐ and nitrite isomers include ?30.57 and ?28.44 kcal mol^?1 for n‐propane‐, ?33.89 and ?32.32 kcal mol^?1 for iso‐propane‐, ?42.78 and ?41.36 kcal mol^?1 for tert‐butane‐nitro compounds and nitrites, respectively. Entropy and heat capacity values are also reported for the lower homologues: nitromethane, nitroethane, and corresponding nitrites. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 181–199, 2010     

Study of Electronic,Optical Absorption and Emission in Pure and Metal‐Decorated Graphene Nanoribbons (C29H14‐X; X=Ni,Fe, Ti,Co+, Al+, Cu+): First Principles Calculations

Density functional theory (DFT) and time‐dependent density functional theory (TDDFT) calculations were performed with the basis sets 6‐31G for DFT and 6‐31G(d), 6‐31+G(d,p) for TDDFT on pure graphene nanoribbon (GNR) C₃₀H₁₄ and metal‐decorated C₂₉H₁₄‐X (MGNRs; X=Ni, Fe, Ti, Co⁺, Al⁺, and Cu⁺). The metal/carbon ratio (X:C 3.45 %) and the doping site were fixed. Electronic properties, that is, the dipole moment, binding energy, and HOMO–LUMO gaps, were calculated. The absorption and emission properties in the visible range (λ=400–720 nm) were determined. Optical gaps, absorption and emission wavelengths, oscillator strengths, and dominant transitions were calculated. Pure graphene was found to be the most stable form. However, of the MGNRs, C₂₉H₁₄?Co⁺ and C₂₉H₁₄?Al⁺ were found to be the most and least stable, respectively. All GNRs were found to have semiconducting nature. The optical absorption of pure graphene undergoes a shift on metal doping. Emission from the pure graphene followed Kasha′s rule, unlike the metal‐doped GNRs.     

Nitrogen‐doped C60 as a robust catalyst for CO oxidation

The O₂ activation and CO oxidation on nitrogen‐doped C₅₉N fullerene are investigated using first‐principles calculations. The calculations indicate that the C₅₉N fullerene is able to activate O₂ molecules resulting in the formation of superoxide species ( ) both kinetically and thermodynamically. The active superoxide can further react with CO to form CO₂ via the Eley–Rideal mechanism by passing a stepwise reaction barrier of only 0.20 eV. Ab initio molecular dynamics (AIMD) simulation is carried out to evidence the feasibility of the Eley–Rideal mechanism. In addition, the second CO oxidation takes place with the remaining atomic O without any activation energy barrier. The full catalytic reaction cycles can occur energetically favorable and suggest a two‐step Eley–Rideal mechanism for CO oxidation with O₂ catalyzed by the C₅₉N fullerene. The catalytic properties of high percentage nitrogen‐doped fullerene (C₄₈N₁₂) is also examined. This work contributes to designing higher effective carbon‐based materials catalysts by a dependable theoretical insight into the catalytic properties of the nitrogen‐doped fullerene. © 2017 Wiley Periodicals, Inc.     

Structure and electronic properties of hollow‐caged C60 fullerene‐derived (MN4)nC6(10 − n) (M = Zn,Mg, Fe,n = 1−6) complexes

Unique hollow‐caged (MN₄)_nC_{6(10 ? n)} (M = Zn, Mg, Fe, n = 1?6) complexes designed by introduction of n porphyrinoid fragments in C₆₀ fullerene structure were proposed and the atomic and electronic structures were calculated using LC‐DFT MPWB95 and M06 potentials and 6‐311G(d)/6‐31G(d) basis sets. The complexes were optimized using various symmetric configurations from the highest O_h to the lowest C₁ point groups in different spin states from S = 0 (singlet) to S = 7 (quindectet) for M = Fe to define energetically preferable atomic and electronic structures. Several metastable complexes were determined and the key role of the metal ions in stabilization of the atomic structure of the complexes was revealed. For Fe₆N₂₄C₂₄, the minimum energy was reported for C_2h, D_2h, and D_4h symmetry of pentet state S = 2, so the complex can be regarded as unique molecular magnet. It was found that the metal partial density of states determine the nature of HOMO and LUMO levels making the clusters promising catalysts. © 2014 Wiley Periodicals, Inc.     

Computed Relative Populations of D2(22)‐C84 Endohedrals with Encapsulated Monomeric and Dimeric Water

Water monomer and dimer encapsulations into D₂(22)‐C₈₄ fullerene are evaluated. The encapsulation energy is computed at the M06‐2X/6‐31++G** level, and it is found that the monomer and dimer storage in C₈₄ yields an energy gain of 10.7 and 17.4 kcal mol^?1, respectively. Encapsulation equilibrium constants are computed by using partition functions based on the M06‐2X/6‐31G** and M06‐2X/6‐31++G** molecular data. Under high‐temperature/high‐pressure conditions, similar to that for the encapsulation of rare gases in fullerenes, the computed (H₂O)₂@C₈₄‐to‐H₂O@C₈₄ ratio is close to 1:2.