Vol 69, No 5 (2024)

Many carborane derivatives, first synthesized during the rapid development of this field of chemistry in the 60s of the last century, remained completely uncharacterized by modern spectral and structural methods. In this work, a series of C-mercuro derivatives of ortho-carborane 1-PhHg-2-Ph-1,2-C₂B₁₀H₁₀ and (2-R-1,2-C₂B₁₀H₁₀)₂Hg (R = H, Me, Ph) were newly synthesized and characterized by NMR spectroscopy. The molecular crystal structure of bis(2-phenyl-ortho-carboran-1-yl)mercury was determined by single crystal X-ray diffraction.

Low-dimensional flakes of transitional metal dichalcogenides TaX₂ (X = S, Se, Te), VSe₂ and NbSe₂ were acquired using liquid-phase exfoliation process. Hansen solubility parameters of those dispersions were estimated by measuring extinction in a number of various liquid environments. Amount of low-dimensional particles of dichalcogenides in a sample increases with decrease of Hansen distance between dichalcogenide and exfoliation medium. We propose a method to qualitatively estimate the impact exfoliation medium has on the size of forming particles and demonstrate how decrease of the absolute value of δ_polar and δ_hydrogen in examined systems leads to decrease in size of forming flakes.

A method has been proposed for the preparation of 1,10-disulfanyl-closo-decaborate anion [1,10-B₁₀H₈(SH)₂]^2-(3). This compound can be easily prepared in several steps. The first stage consists of selective introduction of the zwitterion of iodine at the apical vertices into the closo-decaborate anion (1,10-B₁₀H₈(IPh)₂(1)). At the second stage, this group is replaced by thiodimethylformamide (1,10-B₁₀H₈(SCHNMe₂)₂(2)). At the last third stage, the resulting derivative undergoes hydrazinolysis at the substituted position with the formation of 1,10-disulfanyl-closo-decaborate anion. This compound in its reaction properties is very close to the substituted 2-sulfanyl-closo-decaborate anion at the equatorial position [2-B₁₀H₉(SH)]^2-, which can easily undergo an alkylation reaction in the presence of a base. Bromoacetamide was used as an example, which made it possible to obtain a tetraacetylamide di-sulfonium derivative of the closo-decaborate anion (1,10-B₁₀H₈(S(CH₂C(O)NH₂)₂)₂(4)). The resulting compounds were characterized using multinuclear NMR spectroscopy on ¹¹B, ¹H, ¹³C nuclei, IR spectroscopy and elemental analysis. The structures of compounds 2, 3, 4 were determined by X-ray diffraction analysis. Based on X-ray diffraction data and Hirschfeld surface analysis, crystal packing and intermolecular interactions in compound 4 were studied.

The aim of this research work is to study the effect of substitution in the anionic lattice of inorganic phosphors activated by Eu³⁺ ions with an apatite-type structure of [GeO₄]^4– by [PO₄]³ groups on their luminescent and crystal chemical properties. A number of solid solutions with the general formula Ca₂La_7.2Eu_0.8(GeO₄)_6–x(PO₄)_xO_2+x/2–δ (1) have been synthesized. The reduction of Eu³⁺ to Eu²⁺ in the structure of synthesized crystal phosphors has been shown by methods of luminescent spectroscopy and electron paramagnetic resonance (EPR). For compounds with x = 0.18 and 0.48, the effect of the composition on the strength of the crystal field acting on Eu³⁺ ions is shown. The phonon sublattice was studied using IR and Raman spectroscopy methods. A decrease in the integral luminescence intensity is shown for the selected type of illumination. The obtained data can be used to create effective phosphors for such technological fields as the creation of scitillation detectors, television devices and photodiodes.

Nano-sized powder and nanostructured fibers of nickel-zinc ferrite with the composition Ni_0.5Zn_0.5Fe₂O₄ were synthesized. By means of X-ray diffraction analysis, it was proven that the synthesized samples correspond to the nickel-zinc ferrite phase. Based on the data obtained, it was established that fibers based on nickel-zinc ferrite have a higher value of the crystal lattice parameter and crystallite size than the synthesized nano-sized powder. SEM data confirm that the samples under study consist of nanosized particles: 20–60 nm for powder and 20–40 nm for fibers. The optical diffuse reflection method was used to determine the band gap for Ni_0.5Zn_0.5Fe₂O₄ samples, which was 1.58 eV for fibers and 1.67 eV for powder. The photocatalytic degradation of methylene blue under the action of Ni_0.5Zn_0.5Fe₂O₄ samples of various morphologies has been studied. It was determined that a sample of nanostructured Ni_0.5Zn_0.5Fe₂O₄ fibers has greater photocatalytic activity, since the degree of degradation of methylene blue was 26% for nanofibers and 18% for nanopowder.

New coordination compounds of light rare-earth (RE) bromides with acetylurea (AsUr) were synthesized, [Y(AcUr)₂(H₂O)₄]_1.39[Y(AcUr)₂(H₂O)₅]_0.61Br₆·2H₂O (I), [La(AcUr)₂(H₂O)₅]Br₃ (II), [Ce(AcUr)₂(H₂O)₅]Br₃ (III), [Nd(AcUr)₂(H₂O)₅]Br₃ (IV), [Sm(AcUr)₂(H₂O)₅]Br₃ (V); elemental analysis, IR spectroscopy and X-ray diffraction were used to determine their compositions and structural features. Compound I is built of the [Y(AcUr)₂(H₂O)₄]³⁺ and [Y(AcUr)₂(H₂O)₅]³⁺ cations in the 2.28 : 1; they differ by the number of the inner-sphere water molecules (4 and 5 for coordination numbers 8 and 9, respectively), non-coordinated Br^— ions and H₂O molecules. Compounds II and III are built of the [Ln(AcUr)₂(H₂O)₅]³⁺ (Ln = La, Ce) cations and outer-sphere Br^— ions. The structures changes on cooling from 296 K to 100 K being isostructural at both temperatures. Compounds IV and V have the same composition, but different structures. They also have different polymorphous modifications at 100 and 296 K. Samarium, terbium and dysprosium bromide complexes of acetyl urea show photoluminescence.

Using quantum chemical calculations performed within the framework of electron density functional theory, the structural, mechanical, thermal, electrical and optical properties of three new mixed-type supertetrahedral structures based on the diamond crystal lattice were studied, in which pairs of neighboring carbon atoms are replaced by a pair of tetrahedra, one of which consists of four carbon atoms, and the second of four boron, aluminum or gallium atoms. The calculations have shown that all three crystalline structures should be structurally stable and have a low density, and the density of the aluminum-carbon structure should be even lower than the density of water (0.97 g/cm³). The boron-carbon structure should have the highest hardness (24 GPa), the hardness of the other two structures should be four times lower. All three crystal structures should be narrow-gap semiconductors with a band gap of 0.65–1.87 eV.

The dependence of the electronic structure on the chirality of single-walled SiGe nanotubes has been studied using the quantum chemistry methods. It has been shown that all nanotubes have a semiconductor type of band structure with a band gap E_g of about 0.35 eV, which distinguishes them from silicon analogues, which, depending on chirality, have semiconductor, semimetallic or metallic properties. This difference is due to the polarity of the Si-Ge chemical bond and, as a consequence, the influence of the antisymmetric component of the electronic potential on the band structure of the compounds. The valence band with a width of about 12 eV includes an inner band of predominantly s electrons of atoms with a width of 2 eV and a band of p electrons located above with a width of 8 eV. The energies of the spin-orbit gaps of the edges of the valence band and the conduction band differ significantly: for non-chiral nanotubes, they are equal to several tenths, and for chiral nanotubes, they are several meV. Using mechanical action, for example, by twisting a nanotube around its axis, it is possible to control the energies of spin-orbit gaps, which can find application in spintronics.

The [Сu—C₆F₁₁COOAg] system was studied using thermogravimetry, differential scanning calorimetry and mass spectrometry methods. It has been established that in the temperature range 370–445 K, a solid-phase exchange reaction occurs in the condensed phase of the system with the formation of C₆F₁₁COOCu and silver. The enthalpy of this reaction was found to be ΔrH^o298.15 = –17.5 ± 4.0 and the standard enthalpy of formation of a crystalline copper complex ΔfH^o298.15 = –2769 ± 25 kJ/mol. Sublimation of the copper complex is accompanied by the transition into the gas phase of dimeric (C₆F₁₁COOCu)₂ ΔsH^oТ = 134.4 ± 7.2 kJ/mol and a small amount of tetrameric molecules (C₆F₁₁COOCu)₄. The standard enthalpy of formation of the dimer complex in the gas phase was calculated to be ΔfH^o298.15 = –5404 ± 26 kJ/mol. The paper examines the possibility of exothermic interaction of copper perfluorocyclohexanoate with metallic copper in the condensed phase.

By methods of static magnetic susceptibility, conductometry and spectrophotometry measurements in UV and visible spectra ranges, there were studied physicochemical properties of solutions of perrhenate iron(II) complexes with 2,6-bis(benzimidazol-2-yl)pyridine (L) of composition [FeL₂](ReO₄)₂ ⋅ 1.5H₂O (1) in dimethylsulfoxide (DMSO). As it was established previously, 1 provides a sharp high-temperature spincrossover (SCO) ¹А₁ ↔ ⁵Т₂. The study of the temperature dependence of m_eff(Т) of complex 1 in DMSO showed that the SCO also reveals itself in solution. According to the electrical conductivity of solutions in DMSO at 298 K, the complex 1 in the studied concentration range 3.6 × 10^–6 — 9.12 × 10^–4 M is almost completely dissociated. An absorption peak was found in the UV region of the spectrum, which is practically independent on temperature. In the visible region, two combined absorption peaks are observed at 520–560 nm, which are responsible for the complex formation of FeL²⁺ and FeL₂²⁺ and vary with temperature and L concentration.

Heteronanostructures (ZnS)(Ag₂S)_x with x from 0.002 to 0.50 were synthesized by hydrochemical coprecipitation. The size of ZnS nanoparticles in the resulting heteronanostructures is 2–4 nm. Annealing of synthesized heteronanostructures (ZnS)(Ag₂S)_x in air at temperatures from 25 to 530°C or more leads to a change in their phase composition due to the oxidation of cubic zinc sulfide to hexagonal zinc oxide. Oxidation begins at a temperature of ~250°C, and the zinc oxide content in them after annealing at 530°C reaches ~26–30 wt.%. The size of nanoparticles of the resulting ZnO ranges from 12 to 17–25 nm. A study of the oxidation of (ZnS)(Ag₂S)_x heteronanostructures in air showed that the initial mass loss observed upon heating to ~120°C is due to the removal of adsorbed moisture. The subsequent weight loss that occurs upon heating from ~250 to ~430–450°C is associated with the onset of oxidation of ZnS sulfide and the formation of ZnO oxide. The greatest weight loss is observed upon heating from ~450 to ~580°C and is due to an increase in the ZnO content, partial oxidation of sulfur and its removal in the form of SO₂. The oxidation stages are confirmed by the presence of maxima in the temperature dependences of ion currents corresponding to H₂O, CO₂ and SO₂. The studied heteronanostructures are thermally stable when heated to ~200–250°C.