C72: gaudiene, a hollow and aromatic all-carbon molecule

Peer reviewe

Real-space numerical grid methods in quantum chemistry

Peer reviewe

The aromatic character of [10]annulenes and dicupra[10]annulenes from current density calculations

We have investigated the aromatic properties of seven low-lying isomers of [10]annulene and of the recently synthesized dicupra[10]annulene compounds that were crystallised with two or four lithium counterions (Wei et al., J. Am. Chem. Soc., 2016, 138, 60-63). The molecular structures of the [10]annulene conformers and the dicupra[10]annulenes with bulky trimethylsilyl (TMS) and phenyl groups, as well as the corresponding unsubstituted dicupra[10]annulenes were optimised using density functional theory, employing a semiempirical dispersion correction to consider van der Waals interactions. The structures of the hydrocarbon annulenes were subsequently optimised at the SCS-MP2/def2-QZVPD level. Single-point coupled-cluster calculations with explicit treatment of the electron correlation CCSD(F12)(T) were performed to obtain the relative energies of the hydrocarbon annulenes. Four of the conformations lie close in energy relative to each other. Three substituted and three unsubstituted dicupra[10]annulene structures with either four, two or no Li+ counterions were investigated. Magnetically induced current densities calculated using the GIMIC program were used for the assessment of the aromatic properties of the studied molecules. The conformations of [10] annulene with lowest energies are non-aromatic. The calculations revealed that the electron donation of the lithium atoms to the dicupra[10]annulene core significantly affects the electronic and molecular structures of the dicupra[10]annulenes. The annulene ring is non-planar for all studied dicupra[10]annulenes except for the unsubstituted one with four Li+ counterions, which was also found to be the only molecule that sustains a strong diatropic ring current around the dicupra[10]annulene ring. The other five dicupra[10]annulenes sustain very weak net ring currents and can be considered non-aromatic.Peer reviewe

Aromatic Pathways in Porphycene Derivatives Based on Current-Density Calculations

Magnetically induced current densities are reported for porphycenes at the density functional theory level using gauge-including atomic orbitals, which ensure gauge-origin independence and a fast basis-set convergence of the current densities. We have analyzed the current densities by using the gauge-including magnetically induced current (GIMIC) method. The porphycenes are found to be aromatic. They sustain strong diatropic ring currents. The ring-current pathways have been obtained by integrating the strength of the current density passing selected bonds. The calculations show that the ring current of the porphycenes divides into an outer and inner pathways at the pyrrolic rings. Thus, the ring current involves all 26 pi electrons of the porphycenes, which is similar to the ring current of porphin. No significant local ring currents are sustained by the pyrrolic rings. Dihydroporphycene with four inner hydrogens is found to be antiaromatic with weakly aromatic pyrrolic rings. The six-membered rings in benzoporphycene sustain local paratropic ring currents. The global ring current of dibenzoporphycene divides into an outer and inner pathway at the benzoic rings. Interactions between the inner hydrogen and the neighbor nitrogen are found to be more significant for differences in the H-1 NMR shieldings than variations in global ring-current strengths. We found that the antiaromatic dihydroporphycene has a larger HOMO-LUMO gap but a smaller optical gap than the aromatic porphycene.Peer reviewe

Calculation of vibrationally resolved absorptionand fluorescence spectra of the rylenes

A generating function method was used to simulate the vibrationally resolved absorption and emission spectra of perylene, terrylene and quaterrylene. This method operates on the basis of adiabatic excitation energies and electronic ground and excited state vibrational frequencies. These parameters were calculated using density functional theory with the PBE0 functional for perylene and terrylene and with the BH-LYP functional for quaterrylene. The vertical excitation energies of the lower excited states were calculated using functionals with differing amounts of Hartree-Fock exchange. The optimal functional for each molecule was chosen by comparing these energies to literature excitation energies. Using this technique the calculated absorption spectra and the calculated emission spectrum of perylene were found to be in excellent agreement with the literature experimental spectra after introducing a shift and a scaling factor. The most prominent bands of the absorption spectra were assigned to their respective vibronic transitions.Peer reviewe

Gold(I)···Lanthanide(III) Bonds in Discrete Heterobimetallic Compounds: A Combined Computational and Topological Study : Inorganic Chemistry

The chemical nature of the ligand-unsupported gold(I)–lanthanide(III) bond in the proposed [LnIII(η5-Cp)2][AuIPh2] (Ln–Au; LnIII = LaIII, EuIII, or LuIII; Cp = cyclopentadienide; Ph = phenyl) models is examined from a theoretical viewpoint. The covalent bond-like Au–Ln distances (Au–La, 2.95 Å; Au–Eu, 2.85 Å; Au–Lu, 2.78 Å) result from a strong interaction between the oppositely charged fragments (ΔEintMP2 > 600 kJ mol–1), including the aforementioned metal–metal bond and additional LnIII–Cipso and C–H···π interactions. The Au–Ln bond has been characterized as a chemical bond rather than a strong metallophilic interaction with the aid of energy decomposition analysis, interaction region indicator, and quantum theory of atoms in molecules topological tools. The chemical nature of the Au–Ln bond cannot be fully ascribed to a covalent or an ionic model; an intermediate situation or a charge shift bond is proposed. The [AuIPh2]− anion has also been identified as a suitable lanthanide(III) emission sensitizer for La–Au and Lu–Au.Peer reviewe

Aromatic Pathways in Porphyrinoids by Magnetically Induced Ring Currents

Peer reviewe

Coupled-cluster calculations of the lowest 0-0 bands of the electronic excitation spectrum of naphthalene

Peer reviewe

Magnetic response properties of carbon nano-onions

The magnetic response of a number of double- and triple-layer carbon nano-onions (CNOs) is analyzed by calculating the magnetically induced current density and the induced magnetic field using the pseudo-pi model. Qualitatively the same magnetic response was obtained in calculations at the all-electron level. The calculations show that the CNOs exhibit strong net diatropic (paratropic) ring currents when the external magnetic field points perpendicularly to one of the six-membered (five-membered) rings. They are deshielded inside and shielded outside the CNO; the latter dominates for larger CNOs. The magnetic response originates from a combination of spherical paratropic current densities on the inside of each carbon layer and diatropic current densities on the outside of them. The quantitative differences in the aromaticity of the CNOs as compared to single fullerenes are discussed in terms of ring-current strengths. The magnetic response of some of the CNOs is approximately the sum of the magnetic response of the individual layers, whereas deviations are significant for CNOs containing C-80. For the largest CNOs, the deviation from the sum of the fullerene contributions is larger, especially when the external magnetic field is perpendicular to a six-membered ring.Peer reviewe

Magnetically Induced Currents in [n]Cycloparaphenylenes, n=6-11

Peer reviewe