Journal of Structural Chemistry最新文献

One of the discoveries of high-pressure crystal chemistry of the last 10-20 years is the finding of transition of carbonates from structures with triangular [CO₃]-groups to structures with [CO₄]-tetrahedra and the finding of intermediate compounds with tetrahedrally coordinated carbon atoms in the MO–CO₂ (M = Mg, Ca, Sr, Ba) and M`<sub>2</sub>O–CO<sub>2</sub> (M` = Li, Na, K) systems. The possibility of dynamic stability of the structures of these intermediate compounds at atmospheric pressure was unexpected. In this work, based on the calculation of phonon dispersion curves, we carry out a systematic study of the dynamic stability of sp³-hybridized carbonate structures at atmospheric pressure and compare the obtained results with the available experimental data. As a result, for the first time, we demonstrate that sp³-structures of simple carbonates can also be dynamically stable. Namely, the phonon dispersion curve of MgCO₃-(Pbar{1}) with three-membered rings of [CO₄]-tetrahedra is characterized by the absence of imaginary frequencies at 0 GPa. The extensive comparison with experimental data shows that, based on the calculation of phonon dispersion curves, the possibility of the full decompression and extraction from high pressure environment of sp³-structures can be reliably predicted.

Three new MOFs based on Co(II) cations and anions of 4,8-disulfo-2,6-naphthalenedicarboxylic acid (H₄dsndc) are prepared: [Co(H₂dsndc)(dma)₄] (1), [{Co(H₂O)₂(CH₃OH)(dma)₂}₂Co₂(dma)₂(dsndc)₂]· ·0.5DMA (2), and [{Co(dma)₄}₂Co₂(dma)₂(dsndc)₂]·0.5H₂O (3) (dma, DMA = N,N-dimethylacetamide). Structures of all these compounds are determined by single crystal XRD. For 1, chemical and phase purities are established (CHNS elemental microanalysis, powder XRD, IR spectroscopy) and thermal properties are studied (thermogravimetric analysis). Compound 1 can possibly act as a proton-conducting material due to the presence of non-coordinated acidic carboxylate groups.

The first example of a metal-organic framework containing 4,7-di((–)-borneol)-1,10-phenanthroline (L) is prepared. The [Tb₂(L)₂Cl₂(chdc)₂]·8DMF·H₂O (1) and [Tb₂(L)₂Cl₂(chdc)₂]·4DMA·2.115H₂O (2) (chdc^2– = = trans-1,4-cyclohexanedicarboxylate, DMF = N,N-dimethylformamide, DMA = N,N-dimethylacetamide) compounds are structurally characterized. Compound 1 crystallizes in the (Pbar{1}) chiral space group. Both MOFs have a similar structure of coordination layers with the sql topology, but different 3D packing of the layers. The volume fraction available for the solvent in the pores of 1 and 2 is 27% and 33%, respectively.

Single crystals of complex hexafluoridoindate hydrate Rb₄[Cu²⁺(H₂O)₆](InF₆)₂[Cu⁺(OH)(H₂O)₅]_x(H₂O)_6–6x (x = 0.08) with mixed cations are synthesized for the first time. Its crystal structure is studied. It is composed of Rb⁺ cations surrounded by five fluorine atoms and three water oxygen atoms, complex octahedral [Cu(H₂O)₆]²⁺ cations, [InF₆]^3– anions, and crystallization water molecules. A certain amount of monovalent copper atoms are embedded into the space of crystallization water molecules in the form of its linear diaqua ion H₂O–Cu⁺–OH₂ with short Cu–O distances of 1.78(2) Å and 1.83(2) Å. It is completed to a tetragonal bipyramid by three water molecules and an OH group at significantly longer distances (2.51(3)-2.75(3) Å). The presence of Cu⁺ and OH^– in the complex is indirectly confirmed by IR and X-ray photoelectron spectroscopy (XPS). Under XPS experimental conditions, degradation of the compound is observed, which is accompanied by dehydration, hydrolysis, and considerable Cu²⁺ reduction.

The interaction of Dp44mT and DpC thiosemicarbazones with a model lipid membrane and the effect of cholesterol on their localization are studied by NMR spectroscopy and molecular dynamics. It is shown that Dp44mT is mainly localized at the membrane surface, while DpC can penetrate deeper into the hydrophobic region. Cholesterol pushes both compounds out to the bilayer surface. Interestingly, DpC and Dp44mT have similar antiproliferative activities, even though the former exhibits better penetration ability. This fact indicates the absence of any direct correlation between lipophilicity and activity in this case. Redox activity of iron-containing complexes in the reaction of linoleic acid peroxidation is studied: [Fe(Dp44mT)2]⁺ is active only in the presence of ascorbic acid, [Fe(DpC)2]⁺ is most active, and [Fe(AOBP)2]⁺ is not active, apparently due to the steric factor. Weak redox activity of the [Fe(AOBP)2]⁺ complex correlates with its low antiproliferative activity. The obtained results demonstrate an important role of cholesterol for the distribution of ligands in the membrane, a complex relation between lipophilicity and biological activity, and an essential role of redox properties of iron complexes in their anticancer activity.

Experiments are performed on the interaction between iodine and pyridine in the 1:1 ratio under different conditions. Temperature dependences of the vapor pressure are measured in the I₂–pyridine (py) system by the static tensimetric technique with a membrane null-manometer in the temperature range of 0-300 °C. Based on the analysis of the obtained results and the identification of the products formed by mass spectrometry, IR spectroscopy, and powder X-ray diffraction, schemes are proposed for the processes occurring upon heating. The crystal structure of the ({{[text{pypy}]}^{+}}text{I}_{3}^{-}) compound is determined for the first time by single crystal X-ray diffraction.

The shape of filler particles and features of the interaction between the polymer and the filler can play an important role in the structure formation of polymer nanocomposites. At present, nanoparticles (NPs) of natural aluminosilicates, graphene, MXene, and layered double hydroxides are considered as promising fillers. These NPs can form diverse spatial ordering types within self-assembling polymer matrices. In this work, we analyze the NP effect on the microphase separation in the polymer matrix using the mesoscale computer model of a nanocomposite based on an asymmetric AB diblock copolymer filled with 2D NPs. All computations are performed within dissipative particle dynamics. The results show that at a certain composition of the copolymer (A₇B₁₃), the introduction of NPs into a polymer matrix initiates a transition of the gyroid morphology (GYR) formed by A and B blocks to the lamellar one (LAM) through the formation of an intermediate metastable structure such as perforated lamellas (PL). The GYR-PL-LAM transition is detected in the strong incompatibility mode of copolymer blocks and A blocks with NPs and good compatibility between NPs and B blocks. The observed effect is interesting because of the possible application of 2D NPs in the design of nanocomposites with controlled behavior.

6,8-di-tert-butyl-10H-phenoxazine and 2,6-di-tert-butyl-4-(2-hydroxyphenylimino)cyclohexa-2,5-dienone are prepared by the condensation of o-aminophenol with 3,5-di-tert-butyl-1,2-benzoquinone and 2,6-di-tert-butyl-1,4-quinone, respectively. The compounds are structurally characterized by ¹H and ¹³C NMR spectroscopy, high-resolution mass spectrometry, and XRD.

A combined approach of solid-state NMR spectroscopy and quantum chemical calculations was used to determine the detailed structure of surface vanadia sites. The VO_x model representing the active site of the supported VO_x/SiO₂ catalyst was modeled employing solid-state ⁵¹V NMR spectroscopy and calculations performed using the GIAO (Gauge-Including Atomic Orbital) method. The GIAO method demonstrated better agreement between theoretical and experimental ⁵¹V NMR parameters compared to the GIPAW (Gauge-Including Projector Augmented Waves) method, particularly for compounds featuring short V=O bonds.

We report a quantum chemical study of the electronic structure, energy characteristics, and magnetic properties of isomeric bisphenalenyl radical derivatives with a variable number of six-membered rings in the linker (n = 1, 3, 5). It is shown that the nature and strength of exchange spin–spin coupling between unpaired electrons depends on the type (1,2,3,5-dithiadiazolyl, 1,5-dimethyl-6-oxo-verdazyl, and 2,2,6,6-tetramethylpiperidine-1-oxyl) and the position (central part of the linker fragment or terminal bisphenalenyl atoms) of radicals, and the size of the acene skeleton. It is predicted that there are molecules manifesting exchange interactions (of different types but similar magnitudes) between four paramagnetic centers, thus exhibiting the properties of logical switchers.