Vol 60, No 4 (2019)

The paper presents a first-principle study of electronic structure and dielectric properties of calcium and strontium azides carried out in the framework of the density functional theory using a numerical pseudoatomic orbital basis set and a plane wave basis set. The band spectra and the nature of chemical bonding in these systems are considered. Theoretical values of high-frequency dielectric permittivity tensor and Born effective charges are calculated in the framework of density functional perturbation theory and are reported here for the first time.

The functionalization is known as a structural modification procedure of fullerenes and carbon nanotubes. This method improves the chemical and physical properties, such as reactivity and solubility. This paper intends to theoretically describe the possibility of functionalization of C₂₀ fullerene with the simplest ketene CH₂CO. In the first step, two possible [2+2] and [4+2] cycloaddition reactions between C₂₀ and ketene are considered and simulated theoretically. The results show that the [2+2] reaction is favorable both thermodynamically and kinetically. Also, the IRC analysis of transition states indicates that the reaction takes place via a step-wise mechanism in which a zwitterionic intermediate is generated in a rate-determining step. The solvation effect study based on the CPCM model reveals that by changing the reaction medium from nonpolar to polar, the reaction rate is increased. The NBO analysis and the calculation of global electron density transfer (GEDT) indicate that the reaction involves polar transition states. The calculations of the thermodynamic and kinetic parameters of the [2+2] cycloaddition reaction of bowl C₂₀ with ketene show that this reaction is unfavorable.

The modified Perdew-Wang exchange and correlation method (MPW1PW91) is used to analyze the impact of the external electric field on the total energy, dipole moment, energies of frontier orbitals, HOMO-LUMO gaps, electron affinity, ionization potential, and aromaticity of the C5H₅Ir(PH₃)₃ complex. We explore the percentage compositions of frontier orbitals in terms of the defined groups in the presence and absence of the external electric field. Additionally, a dependence of the global reactivity descriptors on the electric field strength is inspected. The aromaticity of the complex is analyzed by nucleus independent chemical shift values in the presence and absence of the external electric field.

In this paper, dispersion corrected density functional theory (DFT-D3) with the B3LYP method and the 6–31G(d) basis set is used to study the inclusion processes of gabapentin with β-cyclodextrin and the effect of inclusion on the dehydration condensation reaction of gabapentin. The calculation results show that β-cyclodextrin and gabapentin can form stable inclusion complexes in both vacuum and water. B-β-CD_s is the most stable one of four inclusion complexes. After inclusion, the dehydration condensation potential barrier of gabapentin in the β-cyclodextrin cavity is significantly increased. Notably, the reaction barrier of gabapentin in the B-β-CD_s complex (a protonated active group of gabapentin with a small mouth of β-cyclodextrin and its hexatomic ring in the cavity of cyclodextrin) even reaches 331.353 kJ/mol in vacuum and 283.538 kJ/mol in water, respectively. There are two obvious increases of 223.574 kJ/mol in vacuum and 193.932 kJ/mol in water after inclusion. Thus, the inclusion complex of β-cyclodextrin with gabapentin, especially B-β-CD_s, inhibits the dehydration condensation side-reaction of gabapentin most effectively.

Current ideas about the electronic and crystal structures of nitrogen-containing conductive polymers are considered. A comparative critical analysis of literature data on electronic, vibrational, and NMR spectra for different nuclei, and X-ray diffraction data for various forms of polyaniline, polyphenylenediamine, and polypyrrole is presented. Particular attention is paid to the relationship between the electronic and crystal structure of nitrogen-containing polyconjugated systems and their electrical conductivity.

In the reaction of a heterometallic complex of the composition [Li₂Zn₂(piv)₆(py)₂] (piv⁻ is the pivalate anion, py is pyridine) with 2,5-pyridinedicarboxylic acid (H₂pdc) and 4,4′-bipyridyl (4,4′-bpy), molecular complex [Zn(MeOH)₂(Hpdc)₂]·4,4′-bpy (1) is obtained. In the interaction of the same complex with another dicarboxylic acid (1,4-naphthalenedicarboxylic (H₂ndc)) and also in the presence of 4,4′-bipyridyl, heterometallic metal-organic framework (MOF) [{LiZn}₄(4,4′-bpy)(dmf)₂(ndc)₆]·3DMF·H₂O (2) is formed. In the interaction of a polymeric pivalate complex of the composition [Cd₂Eu(piv)₇(H₂O)₂]·nMeCN with thiophenedicarboxylic acid (H₂tdc), layered MOF (Me₂NH₂)₂[Cd(tdc)₂]·1.5DMF·H₂O is obtained (3). The structures of 1–3 are determined by single crystal X-ray diffraction. In the reactions studied, the structures of initial heterometallic {Li₂Zn₂} and {Cd₂Eu} moieties is partially retained only for MOF 2. This coordination polymer is of interest for the study of luminescent and sorption properties. In the other cases, the heterometallic unit is fragmented, which results in the formation of a final product involving only one of two metal cations contained in the initial unit.

Citrate complexes of niobium(V) formed in the interaction of [Nb₆O₁₉]⁸⁻ hexaniobate with citric acid are used for transferring the {NbO}³⁺ niobium group to the pseudo-trilacunary [α-B-As^IIIW₉O₃₃]⁹⁻ anion with the formation of sandwich-type [(AsW₉O₃₃)₂(NbO)₃(H₂O)]⁹⁻ complexes. Slow evaporation of the reaction mixture in the presence of dimethylammonium chloride yields crystalline product (NMe₂H₂)₉[(AsW₉O₃₃)₂(NbO)₃(H₂O)]·44H₂O (1) whose structure is determined by single crystal XRD. When the (NBu₄)⁺ salt (obtained by the exchange reaction between 1 and tetrabutylammonium bromide) of [(AsW₉O₃₃)₂(NbO)₃(H₂O)]⁹⁻ is dissolved in DMF, As³⁺ is oxidized to As⁵⁺ with the formation of a mixture of the Keggin-type [AsW₁₁NbO₄₀]⁴⁻ and [AsW₁₀Nb₂O₄₀]⁵⁻ anions. In an aqueous solution 1 is oxidized by hydrogen peroxide with the formation of a mixture of Keggin anions with different numbers of niobium atoms in the structure.

Interaction of iridium(III) nitro-aqua complexes with 1,10-phenanthroline is studied. Complex anions [Ir(phen)(NO₂)₄]⁻ and [Ir(phen)(OH)(NO₂)₃]⁻ are isolated in the solid phase. The complex Na[Ir(phen)(NO₂)₄](phen)(H₂O) is structurally characterized for the first time. Crystallographic data: \(a = 8.0752(5)\acute{\overset{\circ}{\mathrm{A}}}\), \(b = 11.690(7)\acute{\overset{\circ}{\mathrm{A}}}\), \(c = 14.012(7)\acute{\overset{\circ}{\mathrm{A}}}\), α = 105.55(2)°, β = 91,99(2)°, γ = 103,71(2)° space group P-1, Z = 2, ρ_calc = 1,936 g/cm³. The coordination sphere of the iridium atom has a distorted octahedral geometry. The obtained structure contains an island motif consisting of the pairs of complex anions [Ir(phen)(NO₂)₄]⁻ linked to each other by sodium cations.

The (R)-configuration of the carbinol center formed as a result of diastereospecific reduction of (2S)-2-{2-(1S)-1-(dimethylamino)ethyl]phenyl}-2-hydroxy-1,2-diphenylethanone is established by the XRD method. The analysis of shortened nonvalent intramolecular contacts testifies that the molecule is quite rigid, despite the presence of a large number of single valence bonds. Layered nature of molecular packaging is revealed.

Titanium dioxide nanoparticles representing those in dye-sensitized solar cell photoanodes are modeled by first principles calculations, employing a series of structurally resolved polyoxometalates functionalized with organic ligands via the phosphonate anchoring group as a modeling platform. Previous computational studies on titanium dioxide nanoparticles for dye-sensitized solar cells and water splitting systems are based on artificial cleaving of TiO₂ from bulk crystals, which introduces potential various human-made errors. This manuscript focuses on structurally resolved titanium dioxide nanoparticles determined from X-ray diffraction experiments with a 10⁻³ Å resolution and demonstrates that charge transfer occurs from the organic ligands and oxygen atoms to the core titanium atoms. Also, different TiO₂ nanoparticle geometries contribute to variation in the electronic and optical properties of the organic/TiO₂ nanocomposite system. This computational work on structurally resolved molecularly functionalized titanium dioxide introduces a new way to model the TiO₂ nanoparticle-based optoelectronic device, which eliminates the arbitrariness introduced during artificial cleaving and provides insights on the structure-property relationships of organic molecule-functionalized titanium dioxide nanoparticles for water splitting systems and dye-sensitized solar cells.