Electronic structure and stability of fullerene C82 isolated-pentagon-rule isomers

All nine isolated-pentagon-rule isomers of fullerene C(82) were investigated by the DFT method with the B3LYP functional at the 6-31G, 6-31G*, and 6-31+G* levels. The distribution of single, double, and delocalized π-bonds in the molecules of these isomers is shown for the first time. The obtained results are fully supported by DFT quantum-chemical calculations of electronic and geometrical structures of these isomers. The molecules of isomers 7 (C(3v)), 8 (C(3v)), and 9 (C(2v)) contain some radical substructures (such as the phenalenyl-radical substructure), which indicates that they are unstable and cannot be obtained as empty molecules. Thus, there is a possibility of obtaining them only as endohedral metallofullerenes or exohedral derivatives. Isomers 1 (C(2)), 2 (C(s)), 4 (C(s)), 5 (C(2)), and 6 (C(s)) with closed electronic shell are supposed to be stable, resembling isomer 3 (C(2)), which has just been extracted experimentally as an empty fullerene. We assume they can be produced as empty molecules.     

Electronic structures of the seven C80 isomers

The Su-Schrieffer-Heeger (SSH) model has been extended and solved numerically to study the electronic structures of seven C₈₀ fullerene isomers. Then we analyze the electronic properties of the seven isomers and discuss the difference among their electronic structure. It is found that phonons considered in the SSH model induce different results from recent theoretical studies. We compare our results with those obtained with other methods and discuss the difference.     

Capturing C84 isomers as chlorides and pentafluoroethyl derivatives: C84Cl22 and C84(C2F5)12

A mixture of higher fullerenes C(76)-C(96) was pentafluoroethylated with C(2)F(5)I at 250 °C affording a mixture of C(2)F(5) derivatives. After separation with high-performance liquid chromatography, the second C(2)F(5) derivative of C(84)(16), C(84)(C(2)F(5))(12), was investigated by X-ray crystallography and compared with the known isomer in terms of addition patterns and formation energies. Chlorination of a C(84) isomeric mixture with VCl(4) at 350-400 °C resulted in the formation of C(84)Cl(22). X-ray diffraction study revealed the superposition of several C(84)Cl(22) molecules with different isomeric C(84) cages but the same chlorination pattern.     

Further test of the isolated pentagon rule: Thermodynamic and kinetic stabilities of C84 fullerene isomers

Thermodynamic and kinetic stabilities of 73 C₈₄ fullerene isomers were estimated from the MM3 heats of formation and the recently defined bond resonance energies (BREs), respectively. The BRE represents the contribution of a given π bond in a molecule to the topological resonance energy (TRE). All π bonds shared by two pentagons turned out to be highly reactive without exceptions. C₈₄ fullerene isomers with such π bonds must be incapable of survival during harsh synthetic processes. Thus, the isolated pentagon rule (IPR) proved to be applicable to such large fullerene cages. For sufficiently large fullerenes like C₈₄, some isolated-pentagon isomers are also predicted to be very unstable with highly antiaromatic π bonds. © 1996 by John Wiley & Sons, Inc.     

Crystal and molecular structures of fluorinated derivatives of C60 fullerene

Two solvates of fluorinated derivatives of C₆₀ fullerene were studied by single-crystal X-ray diffraction analysis. The crystals of fluorinated fullerene solvate C₆₀F₁₈·C₆H₅Me belong to the monoclinic system with the unit cell parameters a = 11.532(2) , b = 21.501(3) , c = 16.261(2) , = 101.798(5)°. The fluorinated fullerene molecule with the approximate symmetry C _3v occupies a general position. The crystals of fluorinated fullerene solvate C₆₀F₄₈·2C₆H₃Me₃ belong to the cubic system (a = 23.138(2) ). The C₆₀F₄₈ molecule occupies the special position with the S ₆ symmetry. The experimental molecular geometry agrees with the results of quantum-chemical calculations.     

24 IPR isomers of fullerene C84: Cage deformation as geometrical characteristic of local strains

The structures of 24 IPR‐isomers of C₈₄ fullerene with distributed single, double and delocalized bonds are presented. Obtained results are fully supported by DFT quantum‐chemical calculations of electronic and geometrical structures of these isomers. Two reasons of instability of fullerene molecules are their radical origin and/or high local strain. Distortion of pentagons as well as hexagons with alternating single and double bonds is the most significant geometrical parameter reflecting local strain of a molecule. These distortions are measured as maximal dihedral angles of those cycles and reach 20 degrees in mostly deformed hexagons and pentagons. In contrast high values of dihedral angles in hexagons with delocalized π‐bonds are typical for stable isomers. Other geometric parameters such as valence angles, sums of valence angles and dihedral angles between approximate planes of fused rings have no marked influence on stability. The development of strain‐related criteria for fullerene stability will be helpful in the prediction which isomers might potentially be observable in experiment. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Electronic structures and spectra for triepoxides of fullerene C78O3

The equilibrium structures and relative stabilities of the possible 21 lower‐energy isomers for C₇₈O₃ based on C₇₈ (C_2v) were studied by intermediate neglect of differential overlap (INDO) calculations. It was indicated that the most stable geometry is 28,29,30,31,52,53‐C₇₈O₃, where three oxygen atoms are added to the same hexagon passed by the longest axis of C₇₈ (C_2v) and epoxide structures are formed. Electronic spectra of C₇₈O₃ isomers were investigated based on the optimized geometries. The blue shift of the absorptions for 28,29,30,31,52,53‐C₇₈O₃ compared with that of C₇₈ (C_2v) was rationalized and nature of transition of the peaks discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Spectral identification of fullerene C82 isomers

Ultraviolet photoelectron spectra (UPS) of C(82) isomers have been calculated using hybrid density functional theory in combination with the Gelius model [Proceedings of the International Conference on Electron spectroscopy, edited by D. A. Shirley (North-Holland, Amsterdam, 1972), p. 311; J. Electron Spectrosc. Relat. Phenom. 5, 985 (1974)]. The calculated UPS spectra are found to be isomer dependent and in good agreement with the experimental counterparts. Near-edge x-ray absorption fine structure (NEXAFS), x-ray photoelectron spectroscopy (XPS), x-ray emission spectroscopy, and the resonant inelastic x-ray scattering (RIXS) spectra of three important isomers [3(C(2)), 6(C(s)), and 9(C(2v))] have also been simulated. Strong isomer dependence has also been found for NEXAFS, XPS, and RIXS spectra.     

Some perfluoroalkyl grignard reagents and their derivatives

Some perfluoroalkyl Grignard reagents have been prepared in high yields through halogen-metal exchange reactions between perfluoroalkyl iodides (R_fI) and EtMgBr. Derivatization with Me₃SiCl gave satisfactory yields of the corresponding silylated products in THF. However, ether was a very poor solvent for reaction of R_fMgBr with these chlorosilanes. The exchange reaction between R_fI and EtMgBr was nearly quantitative in ether as evidenced by high yields of the 1-hydroperfluoroalkanes upon hydrolysis, but the major production from the attempted silylation in ether was a trans- vinyl bromide [1], i. e.

Spectral data are presented for several new compounds.     

Electronic structures of some olefins and their radical cations

CNDO/2 calculations of the electronic properties of the series of isomeric butenes and pentenes yield ionization potentials which reproduce the observed trends. These are interpreted in terms of the charge distribution effects of the alkyl groups.

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Zusammenfassung CNDO/2 Rechnungen für die Butan- und Penten-Isomeren ergeben die richtigen Trends für die Ionisierungspotentiale. Sie werden im Zusammenhang mit der Änderung der Ladungsverteilung infolge Methylsubstitution diskutiert.

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Résumé Des calculs CNDO/2 des propriétés électroniques des séries d'isomères du butène et du pentène fournissent des potentiels d'ionisation qui reproduisent les tendances observées. Les distributions de charge calculées pour les molécules sont utilisées pour interpréter les propriétés observées en termes d'effet du substituant alkyle.

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Presented in part at the Eighth Theoretical Chemistry Symposium held at the Batelle Institute, Geneva, Switzerland; March 26–30, 1972.     

Molecular structures of some hydroxyazo compounds and their derivatives

The i.r. absorption spectra of 14 o-hydroxyazophenyl derivatives with increasing number of fused benzene rings of the aryl moiety are studied in solid state, in CCl₄ solution and in nujol mull. The i.r. spectral bands are assigned and indicate that these compounds exist in two tautomer forms. The OH group of the aryl moiety ortho to the azo group is responsible for the hydrazone structure. If solutions in CCl₄ are exposed to sunlight the strongly coloured compounds undergo a rapid bleaching, leading to a destruction of the azo group accompanied by an increase of hydrazone structures.     

Electronic structures and reactivities of polymethine dyes and their derivatives

The peculiarities of the electronic structures of polymethine dyes that contain one or two nitrogen atoms in the chromophore were examined by means of the self-consistent-field (SCF) method within the Pariser-Parr-Pople (PPP) approximation as compared with the electronic structures of the corresponding trimethylidynecyanlnes, viz., benzothiazole and 2-quinoline derivatives, which are spectral sensitizers of silver halide emulsions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1492–1494, November, 1982.     

Electronic structure and stability of C86 fullerene Isolated‐Pentagon‐Rule isomers

All 19 Isolated‐Pentagon‐Rule isomers of fullerene C₈₆ were investigated by Density Functional Theory (DFT) methods with B3LYP functional at 6‐31G, 6‐31G*, and 6‐31+G* levels. Preliminary distribution of single, double, and delocalized pi‐bonds in molecules of these isomers of fullerene C₈₆ is fulfilled. Obtained results are perfectly supported by DFT quantum–chemical calculations of electronic and geometrical structures of these isomers. The main reason of instability of isomers 1, 3–15, 18, and 19 are phenalenyl‐radical substructures. Thus, there is a possibility to obtain them only as endohedral metallofullerenes or exohedral derivatives. Isomer 2 (C₂) is unstable due to higher local molecular strain. It is shown that empty C₈₆ may be produced and extracted only as isomers 16 (C_s) and 17 (C₂). © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Vibrational analysis of buta-1,3-diene and its deutero and 13C derivatives and some of their rotational isomers

The wave numbers of trans-2,3-¹³C₂-buta-1,3-diene were calculated using a scaled quantum-chemical force field found at the MP2/6-31G*//MP2/6-31G* level of theory. The obtained results and the theoretical sets of wave numbers for twelve deutero and ¹³C derivatives of the trans form and five deutero and ¹³C derivatives of the gauche form of buta-1,3-diene found previously at the MP2/6-31G*//MP2/6-31G* level are compared with the corresponding experimental vibrational spectra corrected for the Fermi resonance. Combined analysis of the vibrational spectra of the above mentioned isotopomers was performed.     

Deformation and thermodynamic instability of a C84 fullerene cage

Quantum chemical calculations of electronic and geometric structures were performed for molecules of 24 isomers of C₈₄ fullerenes obeying the isolated pentagons rule. The reasons for the instability of isomers not obtained experimentally were established, and the possibility of obtaining some of them was proven. It was shown that the deformation of hexagons and pentagons is the most important geometric parameter directly connected with the thermodynamic instability of fullerenes having closed shells, reflecting the local strain of the molecules.     

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     

Theoretical investigation of C56 fullerene isomers and related compounds

All the 924 classical isomers of fullerene C(56) have been investigated by PM3, and some most stable isomers are refined with HCTH/3-21G and B3LYP6-31G(d) methods. D(2):003 with the least number of adjacent pentagons is predicted to be the most stable isomer at B3LYP/6-31G(d) level, while C(s):022 and C(2):049 possess nearly degenerate energies with relative energies of 0.03 and 3.90 kcal/mol, respectively. However, as to dianionic C(56)(2-) fullerene, C(2v):011 is predicted to be the most stable isomer. Investigations also show that the encapsulation of Ca atom in C(56) fullerene is exothermic and the metallofullerenes Ca@C(56) can be described as Ca(2+)@C(56)(2-). The computed relative stabilities show that the D(2):003 behaves more thermodynamically stable than other isomers in a wide temperature interval, and C(2v):011 should also be an important component. The electronic isomerization of C(56) (C(2v):011) and C(50) (D(5h):002) indicates that this phenomenon might be rather general in fullerenes and causes different properties, thus bringing about new possible applications of fullerenes. The static second-order hyperpolarizabilities of the three most stable isomers are slightly larger than that of C(60).     

Modeling of the molecular and electronic structures of some mono- and biosmium complexes of fullerene C60

The modeling of the molecular and electronic structures of the following mono- and biosmium complexes of fullerene C₆₀ was performed by quantum chemical methods (MNDO/PM3 and DFT/PBE): (??²-C₆₀)[Os(PPh₃)₂(CO)CNMe], (??²,??²-C₆₀)[Os(PPh₃)₂(CO)(CNMe)]₂, (??²-C₆₀)[Os(PH₃)₂(CO)H], (??²,??²-C₆₀)[Os(PH₃)₂(CO)H]₂, (??²-C₆₀)[Os(PH₃)₂(CO)CNMe], (??²,??²-C₆₀)[Os(PH₃)₂(CO)CNMe]₂, and (5-C₆₀H₅)[Os(C₅H₅)], (5, 5-C₆₀H₁₀)[Os(C₅H₅)]₂.The osmium atoms in the first six complexes are ??²-coordinated by fullerene C₆₀. In the last two complexes, the ??⁵-coordination mode is observed. The structures of the radical anions of these complexes were calculated. The energies of the frontier orbitals were evaluated. The acceptor properties of the complexes are discussed. The electron affinities were estimated in two ways: from the energy of the lowest unoccupied molecular orbital (LUMO) and as the energy difference between the neutral molecule and its radical anion.     

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.     

Electronic structure of C84 and KxC84: Comparison to C60 and graphite

X ray photoemission spectra show ～10 valence band features in C₆₀ and C₈₄ films, although they are less distinct in C₈₄ because of the increased number of valence electrons and the decreased molecular symmetry. The presence of inequivalent carbon atoms in C₈₄ is reflected by the fact that the C 1s main line is ～0.2 eV wider than in C₆₀. The C 1s satellite region of C₈₄ exhibits four features within 15 eV of the main line and shows that the HOMO-LUMO π-π* excitation energy of C₈₄ is ～0.5 eV smaller than in C₆₀. Potassium 2p spectra for K-doped C₈₄ films suggest the formation of a phase with composition K₃C₈₄ with two spectroscopically-distinguishable K sites. A new spectral feature emerges when the K content is increased beyond K₃C₈₄, suggesting a phase transition and a saturated composition of K₆C₈₄, as for K_xC₆₀. These similarities are intriguing since K_xC₈₄ is insulating for all x while K₃C₆₀ is metallic and superconducting.