The GW/BSE Method in Magnetic Fields

The GW approximation and the Bethe–Salpeter equation have been implemented into the Turbomole program package for computations of molecular systems in a strong, finite magnetic field. Complex-valued London orbitals are used as basis functions to ensure gauge-invariant computational results. The implementation has been benchmarked against triplet excitation energies of 36 small to medium-sized molecules against reference values obtained at the approximate coupled-cluster level (CC2 approximation). Finally, a spectacular change of colour from orange to green of the tetracene molecule is induced by applying magnetic fields between 0 and 9,000 T perpendicular to the molecular plane.

X-ray molecular orbital analysis. II. Application to diformohydrazide, (NHCHO)2

The molecular orbitals (MOs) of diformohydrazide have been determined from the electron density measured by X-ray diffraction. The experimental and refinement procedures are explained in detail and the validity of the obtained MOs is assessed from the crystallographic point of view. The X-ray structure factors were measured at 100 K by a four-circle diffractometer avoiding multiple diffraction, the effect of which on the structure factors is comparable to two-centre structure factors. There remained no significant peaks on the residual density map and the R factors reduced significantly. Among the 788 MO coefficients, 731 converged, of which 694 were statistically significant. The C—H and N—H bond distances are 1.032 (2) and 1.033 (3) Å, respectively. The electron densities of theoretical and experimental MOs and the differences between them are illustrated. The overall features of the electron density obtained by X-ray molecular orbital (XMO) analysis are in good agreement with the canonical orbitals calculated by the restricted Hartree Fock (RHF) method. The bonding-electron distribution around the middle of each bond is well represented and the relative phase relationships of the π orbitals are reflected clearly in the electron densities on the plane perpendicular to the molecular plane. However, differences are noticeable around the O atom on the molecular plane. The orbital energies obtained by XMO analysis are about 0.3 a.u. higher than the corresponding canonical orbitals, except for MO10 to MO14 which are about 0.7 a.u. higher. These exceptions are attributed to the N—H...O′′ intermolecular hydrogen bond, which is neglected in the MO models of the present study. The hydrogen bond is supported by significant electron densities at the saddle points between the H(N) and O′′ atoms in MO7, 8, 14 and 17, and by that of O′′-p extended over H(N) in MO21 and 22, while no peaks were found in MO10, 11, 13 and 15. The electron density of each MO clearly exhibits its role in the molecule. Consequently, the MOs obtained by XMO analysis give a fundamental quantum mechanical insight into the real properties of molecules.

Optomechanical switching of adsorption configurations of polar organic molecules by UV radiation pressure

Using photoemission spectroscopy (PES), we have systematically investigated the behavior of polar organic molecule, chloroaluminum phthalocyanine (ClAlPc), adsorbed in the Cl-down configuration on the Ag(111) substrate at low temperature − 195 °C under UV irradiation with a range of different photon fluxes. Judging from the evolution of photoemission spectral line shapes of molecular energy states, we discovered that the Cl atoms are so robustly anchored at Ag(111) that the impinging photons cannot flip the ClAlPc molecules, but instead they crouch them down due to radiation pressure; we observe that the phthalocyanine (Pc) lobes bend down to interact with Ag atoms on the substrate and induce charge transfer from them. As photon flux is increased, radiation pressure on the Pc plane initiates tunneling of the Cl atom through the molecular plane to turn the adsorption configuration of ClAlPc from Cl-down to an upheld Cl-up configuration, elucidating an optomechanical way of manipulating the dipole direction of polar molecules. Finally, work function measurements provide a distinct signature of the resulting upheld Cl-up configuration as it leads to a large increase in vacuum level (VL), ~ 0.4 eV higher than that of a typical flat-on Cl-up configuration driven by thermal annealing.

Anion–Anion Interactions in Aerogen-Bonded Complexes. Influence of Solvent Environment

Ab initio calculations are applied to the question as to whether a AeX5− anion (Ae = Kr, Xe) can engage in a stable complex with another anion: F−, Cl−, or CN−. The latter approaches the central Ae atom from above the molecular plane, along its C5 axis. While the electrostatic repulsion between the two anions prevents their association in the gas phase, immersion of the system in a polar medium allows dimerization to proceed. The aerogen bond is a weak one, with binding energies less than 2 kcal/mol, even in highly polar aqueous solvent. The complexes are metastable in the less polar solvents THF and DMF, with dissociation opposed by a small energy barrier.

Probing the molecular frame of uracil and thymine with high-harmonic generation spectroscopy

We present here HHG spectra of uracil and thymine, computed by a real-time formulation of configuration interaction with single excitations. Spectra are obtained as three-dimensional and molecular-plane averages, and as single-polarisation responses.

d-orbital energy levels in planar [MIIF4]2−, [MII(NH3)4]2+ and [MII(CN)4]2− complexes: the nature of M–L π bonding and the implications for ligand field theory

The ‘coordination voids’ above and below the molecular plane exert significant σ and π ligand field effects.

Crystal structure analysis of the biologically active drug molecule riluzole and riluzolium chloride

This study is an investigation into the crystal structure of the biologically active drug molecule riluzole [RZ, 6-(trifluoromethoxy)-1,3-benzothiazol-2-amine], C8H5F3N2OS, and its derivative, the riluzolium chloride salt [RZHCl, 2-amino-6-(trifluoromethoxy)-1,3-benzothiazol-3-ium chloride], C8H6F3N2OS+·Cl−. In spite of repeated efforts to crystallize the drug, its crystal structure has not been reported to date, hence the current study provides a method for obtaining crystals of both riluzole and its corresponding salt, riluzolium hydrochloride. The salt was obtained by grinding HCl with the drug and crystallizing the obtained solid from dichloromethane. The crystals of riluzole were obtained in the presence of L-glutamic acid and D-glutamic acid in separate experiments. In the crystal structure of RZHCl, the –OCF3 moiety is perpendicular to the molecular plane containing the riluzolium ion, as can be seen by the torsion angle of 107.4 (3)°. In the case of riluzole, the torsion angles of the four different molecules in the asymmetric unit show that in three cases the trifluoromethoxy group is perpendicular to the riluzole molecular plane and only in one molecule does the –OCF3 group lie in the same molecular plane. The crystal structure of riluzole primarily consists of strong N—H...N hydrogen bonds along with weak C—H...F, C—H...S, F...F, C...C and C...S interactions, while that of its salt is stabilized by strong [N—H]+...Cl− and weak C—H...Cl−, N—H...S, C—H...F, C...C, S...N and S...Cl− interactions.

Molecular Simulation of Naphthalene, Phenanthrene, and Pyrene Adsorption on MCM-41

The adsorption of three typical polycyclic aromatic hydrocarbons (PAHs), naphthalene, phenanthrene, and pyrene with different ring numbers, on a common mesoporous material (MCM-41) was simulated based on a well-validated model. The adsorption equilibriums (isotherms), states (angle distributions and density profiles), and interactions (radial distribution functions) of three PAHs within the mesopores were studied in detail. The results show that the simulated isotherms agreed with previous experimental results. Each of the PAHs with flat molecules showed an adsorption configuration that was parallel to the surface of the pore, in the following order according to the degree of arrangement: pyrene (Pyr) > phenanthrene (Phe) > naphthalene (Nap). In terms of the interaction forces, there were no hydrogen bonds or other strong polar forces between the PAHs and MCM-41, and the O–H bond on the adsorbent surface had a unique angle in relation to the PAH molecular plane. The polarities of different H atoms on the PAHs were roughly the same, while those of the C atoms on the PAHs decreased from the molecular centers to the edges. The increasing area of the π-electron plane on the PAHs with the increasing ring number could lead to stronger adsorption interactions, and thus a shorter distance between the adsorbate and the adsorbent.

A molecular crystal with an unprecedentedly long-lived photoexcited state

Gold(iii) atoms reversibly deviate from the molecular plane on receiving thermal and photon energy.

Hydrogen bonding and fluorous weak interactions in the non-isomorphous {4,4′-bis[(2,2,3,3-tetrafluoropropoxy)methyl]-2,2′-bipyridine-κ2 N,N′}dibromidopalladium and -platinum complexes

The polyfluorinated title compounds, [MBr2(C18H16F8N2O2)] or [4,4′-(HCF2CF2CH2OCH2)2-2,2′-bpy]MBr2, (1) (M = Pd and bpy is bipyridine) and (2) (M = Pt), have –CH(α)2OCH(β)2CF2CF2H side chains with methylene H-atom donors at the α and β sites, and methine H-atom donors at the terminal sites, in addition to aromatic H-atom donors. In contrast to the original expectation of isomorphous structures, (1) crystallizes in the space group C2/c and (2) in P21/n, with similar unit-cell volumes and Z = 4. The asymmetric unit of (1) is one half of the molecule, which resides on a crystallographic twofold axis. Both (1) and (2) display stacking of the molecules, indicating a planar (bpy)MBr2 skeleton in each case. The structure of (1) exhibits columns with C—H(β)...Br hydrogen bonds between consecutive layers which conforms to a static (β,β) linkage between layers. In the molecular plane, (1) shows double C—H(α)...Br hydrogen bonds self-repeating along the b axis, the planar molecules being connected into infinite belts. Compound (2) has no crystallographic symmetry and forms π-dimer pairs as supermolecules, which then stack parallel to the a axis. The π-dimer-pair supermolecules exhibit (Pt—)Br...Br(—Pt) contacts [3.6937 (7) Å] to neighbouring π-dimer pairs crosslinking the columns. The structure of (2) reveals many C—H...F(—C) interactions between F atoms and aromatic C—H groups, in addition to those between F atoms and methylene C—H groups.