Nuclear magnetic resonance study of potassium dihydrophosphate

A powder sample of potassium dihydrophosphate KH₂PO₄ has been studied by the ³¹P NMR method in a wide temperature range covering the ferroelectric phase transition. Changes in the position and shape of the resonance line at the transition to the ferroelectric phase have been revealed. The parameters of the chemical shift tensor of ³¹P (isotropic shift, anisotropy, and asymmetry) in the ferroelectric phase have been calculated from the experimental data. A sharp increase in the anisotropy of the tensor at the phase transition has been demonstrated. Dielectric measurements have also been carried out to verify the transition temperature.     

Dianthracenylazatrioxa[8]circulene: Synthesis,Characterization and Application in OLEDs

A soluble, green-blue fluorescent, π-extended azatrioxa[8]circulene was synthesized by oxidative condensation of a 3,6-dihydroxycarbazole and 1,4-anthraquinone by using benzofuran scaffolding. This is the first circulene to incorporate anthracene within its carbon framework. Solvent-dependent fluorescence and bright green electroluminescence accompanied by excimer emission are the key optical properties of this material. The presence of sliding π-stacked columns in the single crystal of dianthracenylazatrioxa[8]circulene is found to cause a very high electron-hopping rate, thus making this material a promising n-type organic semiconductor with an electron mobility predicted to be around 2.26 cm² V⁻¹ s⁻¹. The best organic light-emitting diode (OLED) device based on the dianthracenylazatrioxa[8]circulene fluorescent emitter has a brightness of around 16 000 Cd m⁻² and an external quantum efficiency of 3.3 %. Quantum dot-based OLEDs were fabricated by using dianthracenylazatrioxa[8]circulene as a host matrix material.     

Theoretical investigation of the structure and electronic absorption spectrum of a complex zinc bis-[8-(3,5-difluorophenylsulfanylamino)quinolinate]

Using the quantum-chemical methods of the density functional theory DFT/B3LYP/DGDZVP, of the electron density topological analysis QTAIM, and of the time-dependent density functional theory TDDFT/BMK/DGDZVP, we have studied the structure and spectral properties of the electroluminescent complex zinc bis-[8-(3,5-difluorophenylsulfanylamino)quinolinate]. Good agreement of calculation results with experimental data on the electron density topological characteristics and on the absorption spectrum in the visible and UV ranges has been obtained. Based on the analysis of orbitals and wave functions of the TDDFT/BMK/DGDZVP method, we have elucidated the nature of absorption bands of the complex under study.     

Ab Initio Study of Phosphorescence of Hetero[8]Circulenes

Russian Physics Journal - Quantum chemical calculations of phosphorescence lifetime are performed for the first time by ab initio CC2 and TD-DFT methods for hetero[8]circulenes bearing Si and Ge...     

Theoretical study of vibration spectra of sensitizing dyes for photoelectrical converters based on ruthenium(II) and iridium(III) complexes

Quantum-chemical method of the density functional theory was employed to calculate, with the use of a B3LYP hybrid exchange-correlation functional, the IR absorption and Raman spectra of [Ru(bpy)₂(CN)₂] and [Ir(bpy)₂(CN)₂]⁺ complexes. All the normal vibrational frequencies were analyzed and new assignments of a number of bands in the IR absorption and Raman spectra were made. The role of vibrational motions of metal atoms and ligands in the vibronic deformation of electron shells in the course of electron transfer was discussed. This was done using data on surface-enhanced Raman spectra of [Fe(bpy)₂(CN)₂] and [Ru(bpy)₃]²⁺ complexes adsorbed on the surface of colloid silver.     

Mechanism of nitration of nitrogen-containing heterocyclic <Emphasis Type="Italic">N</Emphasis>-acetonyl derivatives. General approach to the synthesis of <Emphasis Type="Italic">N</Emphasis>-dinitromethylazoles

A general synthetic procedure for the synthesis of N-dinitromethyl derivatives of nitrogen-containing heterocycles has been developed. The procedure includes the destructive nitration of heterocyclic N-acetonyl derivatives of tetrazoles, 1,2,4- and 1,2,3-triazoles, pyrazoles, imidazoles and their bicyclic analogs, as well as imides of carboxylic and sulfonic acids and substituted hydrazines with mixtures of sulfuric and nitric acids. The kinetic study of the reaction mechanism was performed using UV and NMR spectroscopy. It was found that the NO₂ groups were sequentially introduced into the methylene fragment by the addition of the nitronium ion to multiple bonds of intermediate enols followed by hydrolysis of the acetyl moiety. The rate and direction of the enolization (due to the CH₂ and CH₃ groups) of the N-acetonyl compounds in sulfuric acid solutions were determined by the study of the deuterium exchange kinetics. The synthesis of the N-dinitromethyl compounds is complicated by side reactions, such as the decomposition of intermediate α-nitroketone, the nitration of the methyl group in the acetonyl moiety, and the nitration of the dinitromethyl products to trinitromethyl derivatives.     

Application of Bader’s atoms in molecules theory to the description of coordination bonds in the complex compounds of Ca2+ and Mg2+ with methylidene rhodanine and its anion

In the framework of Bader??s atoms in molecules theory a complete analysis of the distribution function of electron density in molecules of complexes of Ca²⁺ and Mg²⁺ with methylidene rhodanine and its anion was carried out. The role of mutual polarization of the metal cation and the ligand in the formation of coordination bonds was demonstrated. The accumulation of electron density in the interatomic space of coordination bonds is assumed to be a consequence of the deformation of the ligand electron shell under the influence of the cation electric field. Based on the magnitude and sign of the Laplacian and the electron energy density at the critical points of coordination bonds the interactions were classified the in terms of the atoms in molecules theory. The energy of the coordination bonds was evaluated using the Espinoza??s formula. The stability of metal-containing rings was considered basing on the values of the bond ellipticity.     

Diazadioxa[8]circulenes: Planar Antiaromatic Cyclooctatetraenes

In this paper we describe a new class of antiaromatic planar cyclooctatetraenes: the diazadioxa[8]circulenes. The synthesis was achieved by means of a new acid‐mediated oxidative dimerization of 3,6‐dihydroxycarbazoles to yield the diazadioxa[8]circulenes in high yields. The synthetic protocol appears to be general, and is a one‐pot transformation in which two C? C bonds and two C? O bonds are formed with the loss of two molecules of water. We also present a detailed characterization of the optical and electrochemical properties of this new class of stable planar cyclooctatetraenes. The properties of the diazadioxa[8]circulenes are compared with the properties of isoelectronic tetraoxa[8]circulenes and azatrioxa[8]circulenes. We discuss the antiaromatic nature of the planar central cyclooctatetraene moiety. The antiaromatic nature of the planar cyclooctatetraenes was studied by using computational methods (NICS calculations), and these calculations reveal that the central eight‐membered ring has antiaromatic character.     

Evolution of NaNO<Subscript>2</Subscript> in porous matrices

NMR and dielectric studies of NaNO₂ loaded into an SBA-15 mesoporous matrix are reported. The spin-lattice relaxation rate and the ²³Na NMR line shift, as well as the permittivity, were measured within a broad temperature interval including the ferroelectric phase transition in NaNO₂. The phase transition temperature of sodium nitrite in as-prepared samples was shown to differ substantially from that characteristic of a bulk crystal. The permittivity grows strongly in the vicinity of the phase transition. Heating a sample causes the properties of NaNO₂ embedded in pores to gradually approach those of bulk crystals.     

Structure of zinc complexes with 3-(pyridin-2-yl)-5-(arylideneiminophenyl)-1H-1,2,4-triazoles in different tautomeric forms: DFT and QTAIM study

On the basis of X-ray crystallographic data on molecular crystals of zinc complexes with 3-(pyridin-2-yl)-5-(arylideneiminophenyl)-1H-1,2,4-triazoles, quantum-chemical analysis of the electron density distribution function for these complexes has been performed by Bader’s atoms in molecules method. Topological parameters of electron density at the critical points of coordination and noncovalent bonds have been interpreted, and the bond energies have been estimated using the Espinosa equation. For the solvated complex Zn[(L3)(OAc)₂] · i-PrOH (L3 = 3-(pyridin-2-yl)-5-(benzylideneiminophenyl)-1H-1,2,4-triazole), a variable coordination number of the Zn²⁺ ion has been predicted as a result of dynamic dissociation/formation of an unstable Zn-O coordination bond. For the binuclear [Zn₂(L2)₂] complex (L2 = 3-(pyridin-2-yl)-5-(salicylideneiminophenyl)-1H-1,2,4-triazole), an orbital interpretation of the decrease in the fluorescence quantum yield in tetrahydrofuran and dimethyl sulfoxide as compared with free L2 ligand is presented.