Molecular and electronic structure of some bowl-shaped unsaturated hydrocarbon molecular systems,possible precursors of C60 fullerene

The AMI calculations of hydrocarbon molecules C₂₀H₁₀ (1) and C₃₀H₁₀ (2) and anions C₂₀H₁₅ ^–4 (3) and C₃₀H₁₅ ^– (4) have been performed with the full energy optimization of the geometric parameters. The chosen topology of the carbon framework of the studied compounds is identical to the topology of the corresponding carbon fragments of C₆₀ fullerene. Analysis of the structure of the frontier orbitals of systems1–4 demonstrated that the tendency of the C₂₀H₁₀ molecule to form sandwich -complexes of the ⁵-type with transition metal atoms is small; however, this tendency is significantly larger than that of C₃₀H₁₀. Moreover, the exclusion of the five-membered cycle of bowlshaped unsaturated hydrocarbon molecules and anions from the conjugated system (as a result of the conversion of five framing C atoms to saturated carbon centers) favors the stabilization of their ⁵-type -complexes with M(C₅H₅) species. The stability of these complexes must approach the stability of classical sandwich complexes of the ferrocene type. The results obtained have been extrapolated to polyhedral C₆₀ and C₇₀ carbon clusters.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 855–858, May, 1995.This work was financially supported by the Russian Foundation for Basic Research (Projects No. 93-03-4101 and 93-03-18725).     

Benzo[a]acecorannulene: surprising formation of a new bowl-shaped aromatic hydrocarbon from an attempted synthesis of 1,2-diazadibenzo[d,m]corannulene

[Structure: see text] Flash vacuum pyrolysis of 7,10-bis(2-bromophenyl)acenaphtho[1,2-d]pyridazine (C26H14Br2N2) has resulted in a surprising transformation, including dinitrogen loss, to give benzo[a]acecorannulene, a novel C26H12 bowl-shaped fullerene fragment.     

The first bowl-shaped stable neutral radical with a corannulene system: synthesis and characterization of the electronic structure

[structure: see text] A bowl-shaped neutral radical with a corannulene system has been designed and synthesized for the first time as a stable solid in air. An unequivocal characterization of the electronic properties of the radical shows that an appreciable amount of spin delocalization extends onto the corannulene unit's curved surface.     

The topology of the Coulomb potential density. A comparison with the electron density,the virial energy density,and the Ehrenfest force density

The topology of the Coulomb potential density has been studied within the context of the theory of Atoms in Molecules and has been compared with the topologies of the electron density, the virial energy density and the Ehrenfest force density. The Coulomb potential density is found to be mainly structurally homeomorphic with the electron density. The Coulomb potential density reproduces the non‐nuclear attractor which is observed experimentally in the molecular graph of the electron density of a Mg dimer, thus, for the first time ever providing an alternative and energetic foundation for the existence of this critical point. © 2017 Wiley Periodicals, Inc.     

Experimental and theoretical electron density study of a highly twisted polycyclic aromatic hydrocarbon: 4-methyl-[4]helicene

Helicenes are molecules of considerable interest in view of their aromaticity which persists despite a marked departure from planarity and because of the extreme potency of some of their metabolites as tumor and mutation promoters. In this study, the electron density of 4-methyl-[4]helicene (or 4-methylbenzo[c]phenanthrene) is studied topologically with an emphasis on the fjord region since this region is where metabolic activation is initiated. The molecule consists of four fused aromatic rings that assume a twisted geometry. This geometry brings two hydrogen atoms into close proximity in the fjord region of the molecule accompanied by the appearance of an intramolecular C-Hdelta+...delta+H-C bond path (an interaction termed hydrogen-hydrogen or H- H bonding to distinguish it from dihydrogen bonding from which it is qualitatively distinct). In addition to the intramolecular H-H interaction, a number of intermolecular interactions are shown to be involved in the packing of this molecule in the crystalline state. The effect of the nonplanarity of the molecule on the local aromaticity of each ring is also discussed.     

On the coordination chemistry of corannulene, the smallest “buckybowl”

A variety of methods, conventional and non-conventional, are used in attempts to prepare the compounds (η⁶-corannulene)M(CO)₃ (M = Cr, Mo, W), all unsuccessful. Conventional methods are also utilized in attempts to prepare the compound [CpFe(η⁶-corannulene)]PF₆, but these result in mixtures of cationic CpFe(arene) complexes containing partially hydrogenated corannulene; similar results have been reported for other polyaromatic hydrocarbons. DFT calculations on the compound (η⁶-corannulene)Cr(CO)₃ suggest that the (η⁶-corannulene)-Cr linkage is only a few kcal/mol weaker than the corresponding bond in (η⁶-benzene)Cr(CO)₃, implying that failures in syntheses arise from kinetic, not thermodynamic problems.     

Estimation of the electron affinities of C60, corannulene,and coronene by using the kinetic method

Novel anions that contain one molecule each of C₆₀ and the polycyclic aromatic hydrocarbon coronene are generated in the gas phase by electron attachment desorption chemical ionization. Collision-induced dissociation reveals that these cluster ions are loosely bonded. Fragmentation of the mass-selected cluster anion yields, as the only products, the intact radical anions of the constituent molecules, namely, the C₆₀ radical anion and the coronene radical anion, in almost identical relative abundances. This result is interpreted as evidence that the cluster ion can be considered as the anion radical of one molecule solvated by the other molecule. The known very high electron affinity of C₆₀ (2.66 eV) and the comparable degree to which C₆₀ and the PAH compete for the electron suggests that dissociation may be controlled by the electron affinity of a portion of the C₆₀ surface, that is, in this case the kinetic method yields information on the local electron affinity of C₆₀. The electron affinity of the bowl-shaped compound corannulene is estimated for the first time to be 0.50 ± 0.10 eV by the kinetic method by using a variety of reference compounds. Unlike coronene, corannulene reacts with C _?? ⁶⁰ in the gas phase to form a covalently bonded, denydrogenated cluster ion. Support for the concept of “local” electron affinity of C₆₀ comes from a theoretical calculation on the electronic structure of C₆₀ anions, which shows evidence for localization of the charge in the C₆₀ molecule. The possibility of electron tunneling in the C₆₀-coronene system is discussed as an alternative explanation for the unusual observation of equal abundances of C₆₀ anions and coronene anions upon dissociation of the corresponding cluster ion.     

Chemical bonding descriptors based on electron density inhomogeneity measure: a comparison with ELI-D

The electron localizability indicator (ELI-D) is suitable to describe certain aspects of the bonding situation of molecules and solids. ELI-D is based on integrals of electron pair density over very small regions. Recently proposed functional C _p , derived from the electron population in regions of fixed amount of electron density inhomogeneity, is based on the same approach as ELI-D, that is, ω-restricted space partitioning. The electron density inhomogeneity is given by the distance of electron density values to the averaged density within chosen region. Thus, in contrast to ELI-D, C _p is a single-electron property. The distance measure depends on a parameter that can be optimized in such way that C _p mimics the topology of the ELI-D distribution for atoms. Such an optimization was performed for the atoms Li to Xe. The optimal parameter p = 0.6 yields the functional C _0.6 that was exemplary applied to a few chosen molecules. In case of molecules the topology of the inner shell and lone-pair regions as given by C _0.6 is comparable with that of the ELI-D representation. However, in the bonding region between the atoms the topology of C _0.6 is dominated by the low density gradient close to the bond critical point. This may result in rather different topologies when comparing C _0.6 and ELI-D.     

Pair density related to one‐electron information for the ground state of spin‐compensated two‐electron systems

The recent study by Joubert on effects of Coulomb repulsions in a many‐electron system has focused attention on an integral identity involving the pair density. This has motivated the derivation presented here of a vectorial differential form related to this integral result. Our differential identity is then illustrated explicitly by using (i) an exact ground‐state wave function for the so‐called Hookean atom having external potential energy (1/2)kr², with k = 1/4, and (ii) Moshinsky's model in which both the interparticle interaction and the external potential are of harmonic type. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

New aluminate with a tetrahedral structure closely related to the c84 fullerene

A new aluminate Sr33Bi(24+delta)Al48O(141+3delta/2), having an F3m cubic structure (a = 25.090 angstroms, Z = 4) and forming a close packed face centered cubic array of "Al84" fullerene geometry, has been discovered. This original structure consists of corner-sharing AlO4 tetrahedra forming "Al84O106" cubic units whose assemblage delimits five types of cages, three of them being empty, one being occupied by strontium, and the fifth one forming the huge spheric fullerene-type cavity. In the latter, strontium, oxygen, and bismuth ions form concentric spheres, with an onion-skin-like configuration. The latter ions are disposed into a compact "Bi16O(52-n[]n)" anion whose the exceptional geometry is characterized by a strong stereoactivity of the 6s2 lone pair of Bi3+.     

Dissecting the concave–convex π‐π interaction in corannulene and sumanene dimers: SAPT(DFT) analysis and performance of DFT dispersion‐corrected methods

The characteristics of the concave–convex π‐π interactions are evaluated in 32 buckybowl dimers formed by corannulene, sumanene, and two substituted sumanenes (with S and CO groups), using symmetry‐adapted perturbation theory [SAPT(DFT)] and density functional theory (DFT). According to our results, the main stabilizing contribution is dispersion, followed by electrostatics. Regarding the ability of DFT methods to reproduce the results obtained with the most expensive and rigorous methods, TPSS‐D seems to be the best option overall, although its results slightly tend to underestimate the interaction energies and to overestimate the equilibrium distances. The other two tested DFT‐D methods, B97‐D2 and B3LYP‐D, supply rather reasonable results as well. M06‐2X, although it is a good option from a geometrical point of view, leads to too weak interactions, with differences with respect to the reference values amounting to about 4 kcal/mol (25% of the total interaction energy). © 2017 Wiley Periodicals, Inc.     

Molecular fragment shape variation index for functional groups and the holographic properties of electron density

For a specific functional group, considered as a molecular fragment, the rest of the molecule produces a range of interactions which influence various properties of the functional group. Considering a family of molecules with the “same” functional group, the range of variations in properties determines the range of chemical reactivity of the functional group, and a similar conclusion is valid for more general molecular fragments. By the application of conventional as well as more advanced indices of fragment properties, including local electron density shape characterization, various shape variation indices can be introduced for fragments, and their relations to the holographic properties of electron densities can be examined.     

The pyridyl-tag strategy applied to the hydrocarbon/perfluorocarbon phase-switching of a porphyrin and a fullerene

A new hydrocarbon/perfluorocarbon phase-switching strategy based on coordination of pyridyl-tagged molecules to a highly fluorinated dicopper-carboxylate complex possessing two accessible axial coordination sites is described. When a chloroform solution of the tetrapyridyl-substituted porphyrin 3 (0.1 mM, 2 mL) is layered on a perfluorodecalin solution of 2 (3.25 mM, 1.5 mL), complete extraction of the porphyrin into the fluorous phase is observed after 30 min of stirring. Quantitative release of both the porphyrin and 2 is achieved simply by adding excess THF to the biphasic system, the THF acting as a pyridine competing ligand. The recovered perfluorocarbon solution containing 2 can be reused for another complexation with the same efficiency. The scope of this approach is emphasized by the phase-switching of a dipyridyl-substituted fullerene, another example of a molecule for which solubilization in perfluorocarbons is very challenging.     

Experimental charge density of octafluoro-1,2-dimethylenecyclobutane: atomic volumes and charges in a perfluorinated hydrocarbon

Octafluoro-1,2-dimethylenecyclobutane, mp. 238 K, was crystallized in situ on a SMART 1000-CCD diffractometer, and high order X-ray diffraction data were collected at 100 K for a charge density determination. A topological analysis was applied and a partitioning of the molecule into atomic regions making use of Bader's zero flux surfaces yielded atomic volumes and charges. Corresponding atomic properties were also derived theoretically from B3LYP/6-311++G(3df,3pd) wavefunctions. While for carbon the volumes and charges are largely dependent on their bonding environment, fluorine has an almost constant atomic volume around 16-17 A3 and a charge between -0.6 and -0.7e, not only in the title compound, but also in two further perfluorinated hydrocarbons, of which the charge densities were determined earlier.     

Critical point representations of electron density maps for the comparison of benzodiazepine-type ligands

A procedure for the comparison of three-dimensional electron density distributions is proposed for similarity searches between pharmacological ligands at various levels of crystallographic resolution. First, a graph representation of molecular electron density distributions is generated using a critical point analysis approach. Pairwise as well as multiple comparisons between the obtained graphs of critical points are then carried out using a Monte Carlo/simulated annealing technique, and results are compared with genetic algorithm solutions.     

Non-nuclear attractor of electron density as a manifestation of the solvated electron

Two or more polar molecules can trap an excess electron either in a dipole-bound fashion where it is located outside of the cluster (dipole-bound electron) or inside the cluster (solvated electron). The topology of the electron density in dipole-bound and solvated-electron clusters has been examined for the paradigm (HF)3- cluster. As spatial confinement of the excess electron increases, a non-nuclear maximum (or attractor) of the electron density eventually forms, which suggests that the solvated electron can be described as a topological atom with its own set of physicochemical properties.     

Hydrogen-abstraction reactions of fully hydrogenated silicon fullerene cages with the amino radical: a density functional study

Structural Chemistry - We applied density functional theory calculations to study reactions NH2 ?+ SinHn fullerenes (n?=?4, 6, 8, 10, 20, 24, 30, 36, and 50). The reactions...