Interaction between chloride ions mediated by carbon nanotubes: a chemical attraction

The interaction between two Cl− ions separated by the wall of a narrow carbon nanotube has been investigated by density functional theory (DFT) and by DFT-based tight binding (DFTB+). The direct Coulomb interaction between the ions is screened by the nanotube, no matter if the latter is conducting or semiconducting. The presence of the ions induces changes in the electronic density of states of the nanotube, which results in an effective attraction between the ions of the order of 0.2–0.3 eV. The interaction of the outside ions with the tube has a covalent component, when the two ions are near there is even a direct chemical attraction between the ions. In contrast to the effective attraction between two Li+ ions reported before (Juarez et al., Phys Chem Chem Phys 22:10,603, 2020), the effect cannot be explained in terms of physical concepts alone. DFTB+ performs well when compared with DFT, and lends itself to fast calculations for large systems.

Pancake-bonding of semiquinone radicals under variable temperature and pressure conditions

The effects of temperature (100–370 K) and pressure (0–6 GPa) on the non-localized two-electron multicentric covalent bonds (`pancake bonding') in closely bound radical dimers were studied using single-crystal X-ray diffraction on a 4-cyano-N-methylpyridinium salt of 5,6-dichloro-2,3-dicyanosemiquinone radical anion (DDQ) as the sample compound. On cooling, the anisotropic structural compression was accompanied by continuous changes in molecular stacking; the discontinuities in the changes in volume and b and c cell parameters suggest that a phase transition occurs between 210 and 240 K. At a pressure of 2.55 GPa, distances between radical dimers shortened to 2.9 Å, which corresponds to distances observed in extended π-bonded polymers. Increasing pressure further to 6 GPa reduced the interplanar separation of the radicals to 2.75 Å. This may indicate that the covalent component of the interaction significantly increased, in accordance with the results of DFT calculations reported elsewhere [Molčanov et al. (2019), Cryst. Growth Des. 19, 391–402].

Особенности формирования электронной структуры при синтезе соединений Ti-=SUB=-2-=/SUB=-AlC, Ti-=SUB=-2-=/SUB=-AlN, Ti-=SUB=-2-=/SUB=-SiC и Ti-=SUB=-2-=/SUB=-SiN

The electronic structure and total energy of the Ti2AlC, Ti2AlN, Ti2SiC, and Ti2SiN compounds are investigated by methods of the density functional theory and pseudopotentials. Electron state density curves have been constructed for crystal systems and for systems differing in order. It has been shown that even in completely disordered systems there is a qualitative similarity of the electronic structure with an electronic structure of the respective crystalline compounds. This similarity is further enhanced as the degree of ordering increases. The total energy of the studied systems grows with increasing disorderance in about the same way for all studied systems except Ti2SiC. In the latter case, it turns out to be much more sensitive to the degree of disordering, which seems to be due to the greater role of the covalent component of interatomic bonds.

Multipole refinement and electron density analysis in natural borosilicate datolite using X-ray diffraction data

The electron density distribution in the layer silicate datolite, Ca[BOH(SiO4)], was analyzed using high-precision single-crystal X-ray diffraction data (Mo Kα, T = 293 K). The Hansen–Coppens multipole model and Bader's topological analysis of the electron density provides a basis for the quantitative characterization of the bonded interaction of datolite. The results are presented both in the form of maps of the electron density distribution and its Laplacian, and in a compact way in terms of the critical points of the electron density. The relative electronegativities are also discussed. It was shown that closed-shell type interactions exist between Ca and O atoms, whereas Si—O and B—O bonds exhibit an intermediate nature with a strong covalent component. An analysis of the topology of the electrostatic potential demonstrates the relevance of considering this physical property to obtain a complete picture of structure-forming factors.

Local Structure of Europium Sites in Oxide Glasses by Nuclear Gamma Resonance

The symmetry and disorder of the Eu3+ site was investigated in some phosphate and borate glasses by means of 151Eu Mössbauer spectroscopy. The quadrupole interaction parameter, which is due to the distortion of the Eu site compared to a cubic symmetry, has been measured together with the asymmetry parameter, which points out the absence of a threefold or fourfold axis of symmetry at the rare earth site. The correlation of the isomer shift with the optical basicity of the glass indicates a covalent component with 6s character in the Eu-O bond. The axial component of the electric field gradient at the Eu site is also correlated with the optical basicity.

Electronic Structure, Charge Transfer and Bonding in Intermetallics Using EELS and Density Functional Theory

ABSTRACTElectron energy loss spectroscopy and density functional theory have been used to show that there is a covalent component to the bonding in NiAl, CoAl and FeAl, between the transition metal atom and Al. There is no charge transfer and no ionic component to the bonding in NiAl and probably not in CoAl and FeAI. The bonding in non-stoichiometric NiAl is studied. Preliminary results are given for a Σ3 boundary in NiAl.

On the qualitative theory of Shockley surface states of the (111) face of NbC and the nature of bonding in this compound

Qualitative theory of Shockley surface states is applied to the analysis of the (111) surface of the niobium carbide crystal. The existence of Shockley states is predicted in two hybridizational gaps. One of (p, t2g) character lies just below the Fermi energy and the other of (eg, t2g) character is at higher energies. The relation between Shockey states and bonding is discussed. A strong (p, t2g) covalent component of the metal-nonmetal bond is found.

Dyeing of Anionically-Modified Polyamide Fibers with Cationic Dyestuffs

The physicochemical principles of the dyeing of two polyamide-6 fibers modified with the monosodium salt of 5-sulphoisophthalic acid at pH 1.8 and 4.5 with an oxazonium dye (Astrazon Blue BG, C.I. 51004) and a thiazonium dye (Methylene Blue, C.I. 52015) are described. Measurements of the zeta potential by the flow-potential method have shown that the fibers have a very highly negatively-charged surface as compared with unmodified types. This decisively promotes the adsorption of the dyestuff cations on the fiber. The uptake of the dye can be described by means of the Langmuir adsorption isotherm as an ion-exchange reaction. It follows from the agreement of dyestuff saturation figures and comonomer contents that the dyestuff is bound stoichiometrically by the sulpho groups (pH 4.5; 80°C). Carboxyl groups probably take no part in the dyestuff binding at pH 1.8 and 4.5. The standard values of the heat of reaction have been determined from the temperature dependence of the equilibrium constants for reactions responsible for the dyestuff binding. They show that the dyestuff/fiber bond contains a covalent component, which is probably due to interactions between the sulphonate group and the dyestuff cation.