Journal of Structural Chemistry最新文献

Two mineral species of the labuntsovite group from Khibiny (sample 1) and Lovozero (sample 2) alkaline massifs are analyzed by single crystal X-ray diffraction and Raman spectroscopy. They are intermediate members of the tsepinite-Na–“tsepinite-Ba”–tsepinite-K solid solution, which are characterized by a high degree of hydration and a low concentration of extra-frame cations. Parameters of monoclinic cells are: a = 14.5086(6) Å, b = 14.2174(6) Å, c = 7.8712(3) Å, β = 117.119(4)°, V = 1444.09(11) Å³ (sample 1) and a = 14.2582(4) Å, b = 13.7541(6) Å, c = 7.7770(2) Å, β = 116.893(4)°, V = 1360.20(9) Å³ (sample 2). Crystal chemical formulas (Z = 2) are: |^A[Na_0.84K_0.6[(H₂O)₄]_5.2]^BK_0.2^CBa_0.25^D[Ca_0.35Na_0.15Fe_0.025(H₂O)]| {M1(Ti_1.2Nb_0.8)M2(Ti_1.1Nb_0.9)(O,OH)₄(Si₄O₁₂)₂} for sample 1 and |^A[Na_1.6(H₂O,H₃O)_0.4]^BK₂^C(Ba_0.51Sr_0.21)^{D [Mn}_0.3Ca_0.2(H₂O)](H₂O)₄|{M1(Ti_1.94Nb_0.06)M2(Ti_1.88Nb_0.12)(O,OH)₄(Si₄O₁₂)₂} for sample 2. The high degree of hydration of sample 1 is expressed in the presence of proton hydrate complexes and tetrahedral [H₂O]₄-associates. Labuntsovite group minerals (LGMs) are characterized by so-called block isomorphism due to different distributions of D cations. Our analysis of heteropolyhedral MT-frameworks in LGMs allows us to determine the topological features of cation networks.

Four-component oxide catalysts MnO_x–CuO–ZrO₂–CeO₂ are synthesized by co-precipitation with varying the calcination temperature from 400 °C to 800 °C. Formation and decomposition processes in mixed oxides are studied by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The redox properties of the obtained samples are tested by temperature-programmed hydrogen reduction, and the catalytic characteristics are examined in the CO oxidation reaction. At 400-600 °C homogeneous solid solution Mn_xCu_yZr_zCe_qO₂ with the fluorite structure is formed. Temperature elevation to 700-800 °C facilitates the gradual decomposition of initial oxide, with manganese and copper cations leaving its composition in the form of highly dispersed CuO and Cu_xMn_3–xO₄ particles. The occurrence of different active states in the catalyst and their transitions into each other under the temperature effect is shown to maintain the high activity in the CO oxidation reaction up to 800 °C.

Based on the experimental data of the X-ray diffraction analysis, radial distribution functions are calculated in a wide concentration range of aqueous cerium nitrate solutions under standard conditions. Different models of the structural organization of systems are elaborated. By the calculation of theoretical functions for each model and their comparison with the experimental ones the optimal variants are revealed. Quantitative characteristics of the structure of the nearest environment of Ce³⁺ and (text{NO}^{-}_3) ions, such as coordination numbers and interparticle distances, are determined along with the types of ionic pairs. The structure of the saturated solution is found to be governed by non-contact ion triples. A decrease in the concentration leads to their transformation into ionic pairs.

A novel copper(II) complex based on N-2-(2-pyridyl)ethyl-2-aminoethanesulfonic acid is prepared, its structure is studied by XRD (CCDC No. 2215117). The crystal of the complex is formed by monomeric [CuLH₂O]NO₃ units. The metal centers of the units have an octahedral coordination environment formed by nitrogen atoms of pyridine and the amino group, oxygen atoms of the sulfo group, and water molecules located in the equatorial plane. On the axial axis, there are oxygen atoms of the sulfo groups of the neighboring ligands forming a 1D coordination polymer.

Features of the crystallization of various compounds on the Nafion polymer substrate from supersaturated aqueous solutions is studied by XRD. The solutions are prepared from natural deionized and deuterium-depleted water. It was earlier established that the swelling of Nafion in natural deionized water clearly demonstrates effects caused by the partial uncoiling of polymer fibers into the liquid volume, but no such effects were observed in deuterium-depleted water. The ab initio calculations performed in the present work show that the uncoiling of lateral Nafion chains with terminal –SO₃H groups and the dissociation of these groups with subsequent formation of hydronium ions and (-text{SO}_3^{-}) structural anionic residues are energetically favorable in the case of the contact with a sufficient amount of water molecules. The influence of these factors on the process of crystal formation on polymer substrates is studied. It is established that the effect of partial uncoiling of polymer chains indeed affects the crystallization, and does it in different ways, depending on the crystal structure. Thus, no differences between XRD patterns of crystals grown on smooth and polymer substrates are observed for the monoclinic lattice of sodium acetate trihydrate. In the case of copper sulfate (with either CuSO₄·5H₂O pentahydrate crystals (triclinic crystal system) or CuSO₄·3H₂O trihydrate crystals (monoclinic crystal system)), copper sulfate trihydrate and pentahydrate are formed on the polymer and smooth substrates, respectively. None of the studied crystals exhibited differences between smooth and polymer substrates for the supersaturated solutions based on deuterium-depleted water, and in both cases a triclinic crystal system of the CuSO₄·5H₂O pentahydrate precipitate is identified for the CuSO₄ aqueous solution. For sucrose, the precipitate amorphization upon the deposition onto the Nafion plate is detected. A theoretical model is proposed to explain the effect of partial polymer chain uncoiling on the growth of crystals, depending on their crystal system, unit cell parameters, and the volumetric ratio of hydrophilic and hydrophobic fragments in the molecular structure.

Molecular, crystal, and electronic structures of a series of 3-arylidene-1-pyrrolinium salts are studied. Trifluoroacetates and nitrates of a number of arylidene pyrrolines containing various substituents in the para-position of the arylidene fragment are analyzed. It is shown that the organic cations have a virtually planar molecular structure that is quite easily distorted due to the mobility of the C–C single bond. Varying the substituent in the arylidene pyrroline structure affects insignificantly the geometric and electronic characteristics of the studied compounds. The nature of the anion has almost no effect on the molecular and electronic structure. In all cases, the crystal packing of the studied compounds is mainly due to the hydrogen bonds and non-covalent interactions involving the π-system and the presence of halogen atoms.

The synthesis and crystal structure of new hydrated lead selenite nitrate Pb₄(SeO₃)₃(NO₃)₂·2H₂O (1) are reported. The crystal structure of 1 ((Pbar{1}), a = 7.2590(2) Å, b = 7.6454(2) Å, c = 14.7293(4) Å, α = 84.386(2)°, β = 78.311(2)°, γ = 83.643(2)°, V = 793.18(4) Å³, R₁ = 3.1%) belongs to a new structure type. It is based on a porous framework composed of [Pb₄(SeO₃)₃]²⁺ layers strongly bound via nitrate anions. Water molecules are located in the channels. Stereochemically active electron pairs of SeO₃E groups are directed toward each other. The structure of 1 is compared with similar architectures involving Pb²⁺ and Se⁴⁺ cations.

A new method is proposed to synthesize ethylenediamine complex [RuNO(en)₂OH]I₂ from K₂[RuNOCl₅], which increases the target product yield to 76%. Subsequent treatment of nitrate salt [RuNO(en)₂ OH](NO₃)₂ with concentrated HF with the precipitation of HClO₄ gives [RuNO(en)₂F](ClO₄)₂ with a quantitative yield. According to the single crystal XRD data, in the [RuNO(en)₂F]²⁺ cationic moiety, nitrosyl and fluoride are in the trans-position relative to each other, and in the ruthenium coordination environment, the equatorial plane is composed of four nitrogen atoms from ethylenediamine ligands. The 450 nm light irradiation of the [RuNO(en)₂F](ClO₄)₂ complex at 80 K results in the formation of metastable linkage isomer MS1 with nitrosyl group coordination through the oxygen atom. According to the IR spectroscopic data, the population of MS1 is about 1%, and the respective vibrational band disappears when heated in a temperature range of 280-310 K. The activation parameters of the MS1–GS (ground state) transition according to the DSC data are E_a = 107.1±6.8 kJ/mol, lnk₀ = 36.1±2.6.

The following series of copper(II) complexes based on di(o-tolyl)phosphinic acid (HL) and 1,10-phenanthroline (phen), 5-chloro-1,10-phenanthroline (Cl-phen), 4,7-dimethyl-1,10-phenanthroline (dmphen), 2,2′-bipyridine (bipy) is prepared and characterized: [Cu(OH)L]_n (1), [Cu(phen)(H₂O)L₂] (2), [Cu(dmphen)(H₂O)L₂] (3), [Cu(Cl-phen)(H₂O)L₂] (4), [Cu(bipy)(H₂O)L₂] (5). According to the XRD data, the phosphinate anion L^– exhibits a monodentate coordination in mononuclear complexes 2–5 and a bidentate-bridge coordination in the polymer complex 1. The cytotoxic activity of the ligands and complexes is studied using the A549 (carcinoma) and MRC5 (non-neoplastic fibroblasts) human lung cell lines. It is shown that the complexes exhibit pronounced dose-dependent cytotoxicity to these cell lines in the 1-50 µM concentration range.

A group of hypothetical compounds Mg₂NA (A = F, Cl, Br, I) with the antichalcopyrite structure is considered. Optimized geometries, structures and compositions of the band spectra at all high-symmetry points of the first Brillouin zone are determined for all compounds. A qualitative and quantitative analysis of chemical bonds is performed using electron density distributions, the electron localization function, and Wannier functions.