A Two-Dimensional Coordination Polymer Based on 1,1':4',1'-Terphenyl-2',4,4',5'-tetracarboxylate

The coordination polymer, [MnL_0.5(H₂O)(phen)] _n (H₄L = 1,1':4',1''-terphenyl-2',4,4'',5'-tetracarboxylic acid, phen = 1,10-phenanthroline), has been solvothermal synthesized and structurally characterized by single-crystal X-ray diffraction. Complex crystallizes in triclinic sp. gr.\(P\bar 1\) with Z = 2. Two carboxylate oxygen atoms in the central phenyl rings from two μ\({u_{{6^ - }}}\)L^4– ligands doubly-bridge two Mn(II) ions to form the dinuclear \(M{n_2}{({O_{CO{O^ - }}})_2}\) unit. Each dinuclear \(M{n_2}{({O_{CO{O^ - }}})_2}\) unit links four L^4– ligands and each L^4–ligand bridges four dinuclear \(M{n_2}{({O_{CO{O^ - }}})_2}\) units to generate a 2D coordination network, which can be rationalized as a binodal (4,4) topological network by considering the dinuclear \(M{n_2}{({O_{CO{O^ - }}})_2}\) units and L^4– ligands as 4-connected nodes.     

Vapor phase epitaxy of CdTe on sapphire substrates in dependence on the vapor-flow orientation

The growth of cadmium telluride films on a structured (0001) sapphire surface oriented at an angle of 44° to the vapor-flow direction and normal to the steps formed along the \(11\overline 2 0\) direction is studied. It is found that this geometry of the vapor source and a substrate (heated to a temperature of 300°С) provides the growth of single-crystal CdTe films if a step height on the substrate surface is more than 1 nm. The results are explained by the occurrence of a longitudinal component of the diffusion flux of СdTe molecules and atoms toward the steps from the inner side and their high density at the step edge from the outer side due to the presence of the Ehrlich–Schwoebel barrier, which ensures the efficient supply of material and minimum supersaturation necessary for the nucleation at the step edge and growth of oriented CdTe islands. The cadmium telluride films that are grown have the \(\left( {110} \right)\left[ {1\overline 1 0} \right]CdTe\left\| {\left( {0001} \right)} \right.\left[ {11\overline 2 0} \right]A{l_2}{O_3}\) orientation and a composition similar to stoichiometric CdTe.     

On the effect of structural and symmetrical features of potassium titanyl phosphate crystals with different contents of niobium,antimony, and zirconium on the second-harmonic intensity

A model is proposed, which shows that, at small deviations from the centrosymmetric state of the atomic structure, the quadratic nonlinear susceptibility of a crystal monotonically decreases with approach of the degree of central symmetry \(\eta _{\overline 1 } \)[φ(r)] of the electric potential function of the crystal structure to unity. The quadratic nonlinear susceptibility of K_{1 ? x} Ti_{1 ? x} Nb _x OPO₄ (x = 0, 0.02, 0.04, 0.11), K_{1 ? x} Ti_{1 ? x} Sb _x OPO₄ (x = 0.01, 0.07, 0.17), and KTi_{1 ? x} Zr _x OPO₄ (x = 0.03, 0.04) crystals has been measured. The degree of central symmetry \(\eta _{\overline 1 } \)[φ(r)] has been calculated for the structures of K_{1 ? x} Ti_{1 ? x} Nb _x OPO₄ (x = 0, 0.04, 0.11), K_{1 ? x} Ti_{1 ? x} Sb _x OPO₄ (x = 0.01, 0.07, 0.17), and KTi_{1 ? x} Zr _x OPO₄ (x = 0.03, 0.04) crystals. It is shown that, at \(\eta _{\overline 1 } \)[φ(r)] > 0.7, the relationship between the quadratic nonlinear susceptibility of the investigated crystals and the degree of their central symmetry \(\eta _{\overline 1 } \)[φ(r)] is in qualitative agreement with the proposed model.     

Manifestation of optical activity at oblique incidence of light in crystals of classes $$\overline 4 $$2 m and $$\overline 4 $$

The polarization azimuths and ellipticities of the reflected and transmitted light have been calculated as functions of the angle of incidence for transparent crystals of classes \(\overline 4 \)2m and \(\overline 4 \). Analytical expressions for these parameters are obtained. It is shown that in the general case the polarization azimuths and ellipticities for a plate cut parallel to the optical axis differ for positive and negative angles of incidence of light.     

Crystal and Molecular Structure of <Emphasis Type="Italic">N</Emphasis>-(Phenylthio)phthalimide

The title compound N-(Phenylthio)phthalimide has been synthesized and characterized by FT-IR, NMR, and X-ray single-crystal determination. The compound crystallizes in the triclinic sp. gr. \(P\bar 1\) with Z = 2. The title compound is not planar. The dihedral angle between the phthalimide and phenyl ring systems is 77.41(8)°. The crystal structure is stabilized by intermolecular π...π and C–H...π interactions.     

Sapphire evolution of the vicinal (0001) sapphire surface upon annealing in air

The evolution of a terrace-step nanostructure (TSN) on the sapphire (0001) surface misoriented by an angle of 0.1° with respect to the (\(10\bar 10\)) plane was observed by atomic force microscopy (AFM) at temperatures from 1273 to 1673 K. It was established that, with an increase in the annealing temperature to 1373 K, the step height attains 0.44 nm at a distance of 220 nm between steps; i.e., heating by 100 K doubles these parameters. In this case, the relief periodicity is retained. Rapid cooling of the substrate to 973 K leads to partial freezing of the surface structure, which makes it possible to observe the transition from one TSN to another. It was established that two steps coalescence upon annealing to 1373 K toward the (\(10\bar 10\)) plane, which has the lowest rigidity and, consequently, the lowest atomic density. The coalescence of two steps at a specified temperature is completed at a sufficiently large distance between the steps, at which their interaction energy is negligible. Upon further annealing of the samples above 1373 K, the steps overgrow to 1 nm; however, their periodicity is broken in this case.     

Study of the nanosiderite from ferruginous quartzites of Kursk magnetic anomaly by transmission electron microscopy

Biogenic siderite consisting of equally crystallographically oriented disklike nanoparticles 5–20 nm in size has been found (using transmission electron microscopy) in oxidized ferruginous quartzites (jaspilites) of the Lebedinsky field of the Kursk magnetic anomaly. Based on microdiffraction data and highresolution images, lowering of the siderite structure symmetry from \(R\overline 3 c\) to \(R\overline 3 \) has been established for the first time. A siderite structure model is proposed to explain this fact. Within this model, vacancies formed as a result of oxidation of some part of Fe²⁺ cations to the Fe³⁺ state are ordered in one of two nonequivalent octahedral sites. Identical crystallographic orientation and nanoparticle morphology have been established for coexisting siderite and hematite. It is suggested that the revealed specific features of nanosiderite are related to its biogenic origin.     

Distortions of the atomic structure of 2/1 approximants of icosahedral quasicrystals

Ideal structures of several 2/1 approximants of icosahedral quasicrystals with the sp. gr. Pm \(\overline 3 \) and Pa \(\overline 3 \) have been constructed. It is shown that most atoms have dodecadhedral local coordination. The structural features of the crystals studied have been analyzed. It is found that displacements of atoms from ideal positions in real crystals tend to increase with an increase in the distance to the center of the approximant projection on the perpendicular space. Large displacements are generally related to the presence of very close neighbors in the ideal structure of the approximant. The importance of the investigation of approximants as a source of information about the structure of polyatomic nanoclusters is indicated.     

Viscous and elastic properties of the nematic in the tetrapalladium organyl-pentadecane system

Temperature dependences of the dielectric anisotropy ?_a, effective rotational viscosity \(\tilde \gamma \), and elastic modulus K ₁₁ of the nematic phase of the tetrapalladium organyl-pentadecane system containing 55 wt % pentadecane have been experimentally studied. The quantities ?_a, \(\tilde \gamma \), and K ₁₁ are shown to decrease: ?_a decreases by a factor of about 2.5; \(\tilde \gamma \), by almost two orders of magnitude; and K ₁₁, by more than an order of magnitude. It is found that an applied electric field induces growth of tetrapalladium organyl crystals at 6–9°C above the nematic-crystallosolvate phase transition temperature.     

Formation of Dislocations and Twins As a Result of Uniaxial Compression of Magnesium Single Crystals: Molecular Dynamics Simulation

An atomistic simulation of the deformation of ideal magnesium crystal along the \([11\bar 20]\) crystallographic axis has been performed. The evolution of structural defects under load at T = 300–350 K is considered in detail. It is established that the nucleation of dislocations in an ideal crystal occurs when the stress reaches a level of 0.1G (G is the shear modulus). The acting deformation modes are found to be prismatic slip of a dislocations and \(\{ 10\bar 13\} \) twinning. The formation of dislocation networks and dislocation sites in the twinning plane is observed. Some reactions are proposed to describe the dislocation evolution in the \((\bar 3034)\) plane.     

Phase transitions in bubble domain structures upon spin reorientation near the compensation point in ferrite-garnet films

The behavior of a hexagonal lattice of bubble domains in a uniaxial thin film of (BiTm)₃(FeGa)₅O₁₂ ferrite garnet with a compensation temperature of 120 K was studied experimentally in a range of change in anisotropy from the easy magnetization axis to the easy magnetization plane. It is shown that the spin reorientation occurs in the temperature range 185–160 K, in which the angular phase (either \(\Phi _{\left\langle {1\bar 1\bar 1} \right\rangle }\) or \(\Phi _{\left\langle {\bar 111} \right\rangle }\)) and the axial phase Φ:_〈111〉 coexist. At 172 K, when the percentages of the angular and axial phases are equal, the lattice parameters of the bubble domains and the domain-wall width change stepwise. At T < 160 K, only a plane magnetic phase exists.     

Specific features of optical activity in various uniaxial crystals

The influence of the antisymmetric part of the gyration pseudotensor on the characteristics of reflected and transmitted light has been considered for crystals of classes 3, 4, and 6. The results are compared with the corresponding data for crystals of classes 32, 422, and 622 with a symmetric gyration pseudotensor. Specific features of the optical activity in crystals of classes 3m, 4mm, and 6mm with an antisymmetric gyration pseudotensor have been studied. Crystals of classes \(\bar 42m\) and \(\bar 4\) with the symmetric gyration pseudotensor of an unusual form have been considered. The polarization azimuth and ellipticity of the reflected and transmitted light are calculated for these crystals at different angles of incidence.     

Separate determination of the amplitude of thermal vibrations and static atomic displacements in titanium carbide by neutron diffraction

The amplitude of thermal (dynamic) atomic vibrations and meansquare static atomic displacements in titanium carbide TiC _x (x = 0.97, 0.88, 0.70) have been separately determined by measuring neutron diffraction patterns at two temperatures (T ₁ = 300 K and T ₂ = 80 K). The static lattice distortions in stoichiometric titanium carbide are experimentally found to be negligible. In the TiC _x homogeneity range, the amplitude \(\sqrt {\overline {u_{dyn}^2 } } \) of thermal atomic vibrations significantly increases with a decrease in the carbon concentration. The Debye temperature has been determined for the first time in the TiC _x homogeneity range at both room and liquid-nitrogen temperatures.     

Peculiar reflections in diffraction patterns as indicators of structural type and quality

Reflections serving as indicators of the types of packets forming crystal structures of many layered semiconductors have been revealed in diffraction patterns. It is found that the values l for the strongest reflection in series 000l and 00l, as well as the next to the strongest reflection in series \(hh\bar 2\bar hl\) (h = const) and 0kl (k = const) for hexagonal and monoclinic structures, respectively, determine the number of polyhedral (Tand O) cation-filled layers per cell and indicate the types of packets TOT \(TO\bar TE\) , \(TO\bar T\bar TE\) , \(TOO\bar TE\) , \(TTO\bar T\bar TE\) , \(OOE_1 TO\bar TE_1 \) and OOE \(OOE_1 TO\bar TE_2 TO\bar TE_1 \) , where T and \(\bar T\) are inversely oriented tetrahedra, O is an octahedron, E is an empty interpacket layer, and E₁ and E₂ are partially filled (to less than 1/3) interpacket layers.     

First-principles estimate of Peierls energy in sodium chloride

The Peierls barrier height for edge dislocations in sodium chloride crystal has been estimated from first principles based on the density functional theory. The calculation was performed using a plane-wave expansion of the Bloch functions of a periodic structure with sp. gr. Pmmm and a supercell containing an edge dislocation dipole of dominating slip system \({1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}\langle 110\rangle \{ \overline 1 10\} \). It is shown within the generalized gradient approximation for the exchange-correlation energy that, among the two symmetric positions of dislocation line in the Peierls relief, configuration I, which has a compact core of size d ≈ b (b is the Burgers vector length), is characterized by minimum energy. The second symmetric position corresponds to configuration II with an extended core (d ≈ 2b). Its energy exceeds the Peierls relief minimum by 1.2 × 10^–2 eV (per lattice period). An application of compressive stress changes the form of crystalline relief: its minimum moves to position II.     

Crystallographic analysis of 9-(3-methylbut2-enyloxyfurano)[3,2-g] benzopyran-2-one

This structure of 9-(3-methylbut-2-enyloxyfurano)[3,2-g] benzopyran-2-one has been determined by X-ray diffraction methods. The compound crystallizes in the triclinic (space group P \(bar 1\)) with the unit cell parameters a = 11.1150(10), b = 11.8240(10), c = 11.9290(10) Å, α = 64.90(1)^°, β = 83.53(1)^°, γ = 89.25(1)^° and Z = 4. The structure has been solved by direct methods and refined to reliability index of 0.043. The unit cell contains two crystallographically independent molecules in the asymmetric unit, which exhibit different side-chain conformations. The crystal structure is stabilized by the intra molecular and intermolecular C–H?sO interactions.     

Ferroelastic phase transitions in fluorides with cryolite and elpasolite structures

The ferroelastic phase transitions are investigated in several series of fluoride crystals belonging to the elpasolite and cryolite families (space group \(Fm\bar 3m\)) with the general formula A₂BB′ F₆. The influence of the size and shape of cations and anions on the entropy and the mechanism of structural distortions is discussed.     

Aquanitrilotris(methylenephosphonato)dirubidium [Rb<Subscript>2</Subscript>(H<Subscript>2</Subscript>O){μ<Superscript>12</Superscript>-NH(CH<Subscript>2</Subscript>PO<Subscript>3</Subscript>H)<Subscript>3</Subscript>}]: Synthesis and structure

Aquanitrilotris(methylenephosphonato)dirubidium is a 3D coordination polymer with a layer structure. Space group \(P\bar 1\), Z = 2; a = 8.0380(3) Å, b = 9.0522(4) Å, and c = 10.7837(4) Å; α = 113.252(4)°, β = 105.391(3)°, and γ = 96.182(3)°. Rb atoms populate two symmetrically inequivalent positions with c.n. = 8 and 10; significant difference in O–Rb–O angles in the coordination polyhedra is indicative of the ionic type of Rb–O bonds. In the crystal packing, molecules are connected by not only coordination bonds but hydrogen bonds as well.     

Preparation,characterisation, and crystal structure analysis of (2<Emphasis Type="Italic">E</Emphasis>,2′<Emphasis Type="Italic">E</Emphasis>)-3,3′-(1,4-phenylene)bis(1-(2-aminophenyl)prop-2-en-1-one

A novel bis-chalcone, (2E,2′E)-3,3′-(1,4-phenylene)bis(1-(2-aminophenyl)prop-2-en-1-one) is synthesized through a base catalyzed Claisen-Schmidt condensation reaction of terephthalaldehyde with 2-aminoacetophenone. Its structure (sp. gr. P\(\bar 1\), Z = 2) is determined from single crystal X-ray diffraction data. There are two independent centrosymmetric molecules with no significant differences in bond lengths and angles between them. The NMR, IR, HRMS, and UV spectral data of the prepared bis-chalcone are presented.