Том 60, № 5 (2019)

A diagram in the coordinates “temperature-ionic radius” is built for polymorphic and morphotropic transitions in a series of REE orthoborates. The stability fields are determined for the structural types of calcite, aragonite, vaterite, pseudo-vaterite, H-LaBO₃, and L-SmBO₃. The temperatures of some metastable phase transformations are estimated.

Protonated NH₅²⁺ has unusual vibrational and rotational behavior because its three nonequivalent equilibrium structures have nearly identical energies and its five protons scramble freely, while in the CH₅⁺ structure, five hydrogen atoms are bonded to the carbon atom by sharing eight valence electrons. Although a few theoretical papers have been published on quantum mechanics of those systems. Better understanding requires spectral and conformational analyses. CASSCF (8, 9) calculations with the correlation consistent polarized valence double and triple zeta basis sets are accomplished for estimating the vibrational data and zero-point energies of those two ions. The present results indicate that normal modes agree qualitatively with NH_xD_{(5- x)}²⁺ and one of the normal modes indicates that NH₅²⁺ is highly fluxional and has a complex spectrum while the broken N-H bonds are reformed all the time. The spectrum of mode 10 is highly complex with red and some blue shifts. In particular, modes 6 and 12 are attributed to the rapid coupling of the N-H stretching normal mode to motions more closely related to isomerization, i.e., bending or rocking. There have been long debates whether NH₅²⁺ has a structure at all or not and if the rotation is real or artefactual.

The instability of planar structures in [C₂X₄]⁻ (X = H, F, Cl, Br) molecules due to the pseudo Jahn-Teller effect (PJTE) is investigated as an original PJTE study. Optimization and the following frequency calculations in these molecules illustrate that all of these compounds are unstable in high symmetry planar (with D_2h symmetry) geometry and their structures are distorted to a lower C_2h symmetry stable geometry. Moreover, the vibronic coupling interaction between ²B_2g ground and ²A_g excited states via the (²B_2g + ²A_g) ⊗B_2g PJTE problem is the reason for the symmetry breaking phenomenon and non-planarity in those series. Natural bond analysis (NBO) is used for illustrating the strongest interaction and natural atomic charges of these structures.

In the present study, the competition between the intramolecular hydrogen bond (IMHB) and the π-electron delocalization (π-ED) in some derivatives of triformylmethane (TFM) are investigated. In this regard, all of the hydrogen bonded structures are optimized by B3LYP and MP2 methods with the 6-311++G(d,p) basis set. The relative energies clearly predict that the B conformers (cis and trans) are more stable than the A and C ones; B < A < C. This order can be related to their IMHB strength and π-ED. Accordingly, IMHB and π-ED of all hydrogen bonded structures are comprehensively investigated. The IMHB results show that the O™H ⋯ O unit of A conformers is stronger than the corresponding interactions of other forms and is not consistent with the stability order. On the other hand, the π-electron delocalization of B forms are greater than those of A and C ones, which strongly support the stability order. Consequently, in the benchmark systems, the π-electron delocalization is a superior factor in determining the most stable structures.

At present, there exists subjectivity in selecting descriptor sets for the quantitative structure property relationship (QSPR) models. A complete set is perfect, in which there is no any element redundant or needed to be added. This paper reports the complete sets of descriptors used to develop QSPR models for ¹³C NMR chemical shifts (δ_C parameters) of carbon atoms in quinolone derivatives. These descriptors in the complete sets used are calculated by applying the PBE1PBE functional of density functional theory (DFT) and the 6-311G(2d,2p) basis set. The multiple linear regression (MLR) technique and the support vector machine (SVM) algorithm are, respectively, used to develop linear and nonlinear QSPR models for δ_C parameters. The four QSPR models have the root mean square (RMS) errors less than 2.0 ppm, which approximately equal one fourth of the errors from the previous model. Further, our models have more samples in the test sets and less descriptors in the models. These results suggest that our four models of δ_C parameters have better statistical qualities. The feasibility of applying complete sets of descriptors to develop QSPR models for ¹³C NMR chemical shifts is demonstrated.

Complex oxides with general compositions SmCaCo_1−xFe_xO_4−δ and Sm_0.9Ca_1.1Fe_1−yCo_yCO_4−δ are synthesized using the glycerol-nitrate technique at 1100 °C in air. By powder X-ray diffraction it is determined that SmCaCo_1−xFe_xO_4−δ solid solutions exist in a composition range 0 ≤ x ≤ 0.3 and Sm_0.9Ca_1.1Fe_1−yCo_yO_4−δ solid solutions exist in a composition range 0 ≤ y ≤ 0.7. The samples with high concentrations of cobalt ions are found to crystallize in the tetragonal unit cell (space group I4/mmm), whereas the solid solutions enriched with iron ions have the orthorhombic structure (space group Bmab). For all single phase samples the unit cell parameters and volume and the structural parameters (atomic coordinates and bond lengths) are calculated by the full-profile Rietveld method.

A two-dimensional Zn(II) complex [Zn(BIBP)(TBIP)]_n (1) (BIBP = 1,4-bis(4-(imidazole-1-yl)benzyl)piperazine, H₂TBIP = 5-tert-butyl isophthalic acid) is synthesized and characterized using single crystal X-ray diffraction, IR spectroscopy, and elemental analysis. The single crystal X-ray diffraction analysis reveals that complex 1 is an achiral two-dimensional layer based on 1D left- and right-handed helical [Zn(BIBP)]_n² chains, which are linked by C—H⋯O hydrogen bonds to form a three-dimensional supramolecular framework. Moreover, complex 1 exhibits an emission band at 393 nm (λ_ex = 244 nm).

By a reaction of lanthanide nitrates with trans-1,4-cyclohexane dicarboxylic acid H₂chdc in an aqueous medium new coordination polymers with the composition [Ln₂(H₂O)₄(chdc)₃] (Ln = Ce (1), Sm (2), Eu (3), Gd (4)) are obtained. Crystallization conditions are optimized with the use of a hexamine-based pH buffer. Compound 1 is additionally characterized by powder X-ray diffraction, elemental and thermogravimetric analyses, and IR spectroscopy. The structure of the obtained compounds is determined by single crystal X-ray diffraction. In a series of isostructural three-dimensional frameworks [Ln₂(H₂O)₄(chdc)₃] (Ln = La—Eu, except Pm) a regular change in the structural features is analyzed. The [Gd₂(H₂O)₄(chdc)₃] compound has a similar composition but the topology of the three-dimensional network differs from that of the previous ones due to a decrease in the coordination number of metal centers. Heavier lanthanides, starting from Tb³⁺, and also yttrium(III) do not form compounds with the mentioned composition under similar reaction conditions.

The microstructure of an a-TiO₂:ZnO system obtained by two different synthesis techniques is investigated. Equimolar a-TiO₂:ZnO is subjected to high-energy planetary ball milling as a dry mechanical technique and a solvothermal method as a wet technique for preparing zinc titanates. The investigation is performed by XRD and HR-TEM. The mechanical route results in the formation of ZnTiO₃ as a major product accompanied by Zn₂Ti₃O₈ as a minor one. The solvothermal route results in the formation of Zn₂Ti₃O₈ accompanied by traces of zincite. The thermal stability of later zinc titanate is explored under different temperatures and results in a homogeneous amorphous nanocrystalline phase transformation without a compositional change.

This paper describes a series of new polyamides containing bis(thiosemicarbazone) acenaphthenequinone (PA), bis(thiosemicarbazone) acenaphthenequinone zinc (Z-PA), and bis(thiosemicarbazone) acenaphthenequinone mercury (H-PA) complexes loaded onto MWCNTs synthesized via a chemical precipitation method in methanol followed by antimicrobial activity studies on the novel functionalized MWCNTs complexes. These complexes are characterized by FT-IR spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The antibacterial activity of free PA, Z-PA, and H-PA complexes loaded onto MWCNTs are studied against gram-positive and gram-negative bacteria. The results indicate that the HPA/MWCNT complex is the most effective growth inhibitor against Listeria monocytogenes and Pseudomonas aeruginosa, exhibiting the potential for the use as an antibacterial agent.

In the original article there was a mistake in the information of the corresponding author. The correct spelling of the names of the authors and their order is: J. Qian, J. Wang*, and N.-N. Chen.