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By thermodynamic simulation of the Pr−Se−I system, the optimal growth conditions for new crystalline praseodymium polyselenide PrSe_1.95, whose existence was proved in our previous works, are determined. Based on the obtained information, the PrSe_1.95 crystals are grown by the vapor transport technique using iodine as the transport agent. The crystals produced are identified by microprobe and powder X-ray diffraction analysis. Single crystal X-ray diffraction shows that the crystals are not monophasic, but consist of blocks with tetragonal and monoclinic symmetries, which have a common structural prototype (PbFCl). For two different crystals cut out of a larger one, the structure is determined and the composition is refined. The results of powder and single crystal X-ray diffraction analyses of one of these crystals (monoclinic one) coincide.

A crystallographic analysis of ellisite Tl₃AsS₃, fangite Tl₃AsS₄, lorandite TlAsS₂, and synthetic Tl₃AsS₃ shows that the configuration of atomic positions in these structures is determined mostly by the ordering of S^2– anions and the large massive Tl⁺ cations in a single packing. The standard coordination of the As cation is provided only by the strong covalent As–S bonds; the environment of Tl⁺ cations varies depending on the geometry of their packing with sulfur.

The results of the application of stoichiographic method of differential dissolution (DD) to analyze mixed oxides with the perovskite-like structure are presented. The samples of Sr₁Ti_0.9Mg_0.1O₃ with the ABO₃ stoichiometry of perovskite and samples of Sr₂Ti_0.9Mg_0.1O₄ with the A₂BO₄ stoichiometry of layered perovskite (where A = Sr²⁺; B = Ti⁴⁺, Mg²⁺) are prepared by a mechanochemical method and analyzed before and after catalytic tests. Conditions of the detection, identification, and quantitative determination of different phases in the compositions of the samples are described. The surface comppositions of the initial samples are determined by the DD method, and changes observed after the catalytic tests are noted. The DD results are compared with the powder XRD results.

The crystal structure of the solid solution of alum NH₄Al_0.43Fe_0.57(SO₄)₂×12H₂O (I) is studied in the space group Ра3(-) and its maximal subgroups R3(-), P1(-), and P1. In centrosymmetric space groups sulfate ions occupy one of two opposite orientations, and in the triclinic group P1 four of eight tetrahedra have the same orientation. The second harmonic generation is observed when a train of chirped optical pulses of ytterbium diode pumped solid state laser passes through the crystal of I.

Mononuclear complexes TBA[Bi(NN)I₄] (TBA = tetra-n-butylammonium, NN = 2,2'-bipyridyl (1) and 1,10-phenanthroline (2)) are synthesized by the reaction of BiI₃, tetra-n-butylammonium iodide, and the corresponding ligand in acetone with subsequent crystallization from a benzene-acetone mixture. By changing the solvent used in crystallization to ethanol, binuclear [Bi₂(NN)₂I₆] complexes (3 and 4) are produced. The crystal structure of the compounds is determined by single crystal X-ray diffraction.

Three isostructural iron monophosphates KNiFe(PO₄)₂ (KNi), KMgFe(PO₄)₂ (KMg-LT, where LT means "low-temperature stable phase"), and KCoFe(PO₄)₂ (KCo-LT) are synthesized and structurally characterized from X-ray diffraction data. They crystallize in the monoclinic system with the space group P2₁/c. Their structures have in common a three-dimensional framework, built up by infinite zigzag chains of edge-sharing MO₆ (M = Ni, Mg or Co) octahedra, linked by FeO₅ and PO₄ polyhedra via vertices and edges to form a rigid skeleton. The K⁺ ions are located in formed tunnels. DTA showed that KNi has a congruent melting at 941 °C, whereas KMg-LT and KCo-LT undergo irreversible phase transitions from P2₁/c to different high-temperature structures with the C2/c symmetry. IR absorption bands are assigned to different vibrations of the PO₄ tetrahedron.

A new 2D cobalt(II) coordination polymers namely {[Co₂(btec)(L)₂]×4H₂O}_n (1), where btec = 1,2,4,5-benzenetetracarboxylate and L = 1,3-bis(5,6-dimethylbenzimidazol-l-yl)-2-propanol, are hydrothermally synthesized and characterized by elemental analyses, IR spectroscopy, and single crystal X-ray diffraction analyses. The structure analysis indicates that the compound belongs to the triclinic system, space group Pī, a = 12.198(2) Å, b = 15.0750(2) Å, c = 15.194(2) Å, α = 77.420(2)°, β = 77.872(2)°, γ = 85.538(2)°, V = 2664.2(5) ų, Z = 2. The complex possesses a binodal (3,4)-connected two-dimensional layered structure bridged by btec and L ligands. The fluorescence and catalytic properties of the complex are also investigated.

The reaction of [Pt₂(μ-Se)₂(PPh₃)₄] with diphenyliodonium bromide gave [Pt₂(μ-Se)(μ-SePh)×(PPh₃)₄]⁺ through arylation of a selenide ligand. The complex is characterised by ³¹P NMR spectroscopy, elemental microanalysis, ESI mass spectrometry, and a single crystal X-ray diffraction study, which showed the four-membered {Pt₂Se₂} ring to be slightly puckered.

The possibilities of studying the local structure in isomorphic systems by methods based on the minimization of the interatomic interaction energy are considered in the work. The original procedure for the theoretical analysis of the local structure, which the authors have been developing for a number of years and have implemented in four computer programs, is discussed in detail. The practical implementation of this procedure is exemplified by the following solid substitution solutions: halite-sylvin (Na,K)Cl, corundum-eskolaite (Al,Cr)₂O₃, spinel-magnesiochromite Mg(Al,Cr)₂O₄, chrysoberyl-mariinskite Be(Al,Сr)₂O₄, grossular-uvarovite Ca₃(Al,Cr)₂[SiO₄]₃. Calculations are performed on a SKIF MGU Chebyshev supercomputer for supercells containing several thousands of atoms. The performed analysis of the behavior of changes in the geometric characteristics of CrO ₆ octahedra in various isomorphic systems makes it possible to reveal the main reasons affecting the alteration of the relaxation parameter. It is found that the key factor is the size of the common structural unit of an isomorphic mixture. Thus, the behavior of the relaxation parameter obeys the isomorphism assistance rule.

A variational method of the solution of anharmonic problems in the theory of molecular vibrations in curvilinear coordinates (central force) with accurate taking into account the kinematic anharmonicity is proposed. The simplicity of computational procedures provides the application of this approach to the analysis of states of large molecules.