Home – Home – Jornals – Journal of Structural Chemistry 2017 number 5

Structural, dynamic, and thermodynamic features of double hydrates of xenon and nitrous oxide are calculated. Thermodynamic stability regions of these hydrates are found. At the atmospheric pressure the xenon hydrate is in the equilibrium with the gas phase at temperatures up to 263 K, whereas at these pressures the nitrous oxide hydrate decomposes already at 218 K. A strong dependence of the equilibrium temperatures and pressures of the formation/decomposition of double nitrous oxide and xenon hydrates on the composition of their mixture in the gas phase is shown.

The quantum chemical calculations of induced electric currents in (μ-H)₂Fe₃(μ₃-Q)(CO)₉ complexes, where Q = S, Se, Te, are carried out. It is demonstrated that the appearance of anomalous ¹Н NMR chemical shifts on bridging hydrogen atoms is, first of all, due to the effect of induced currents on iron atoms.

The electronic structure of calix[4]arene phosphine oxides (CPO) and thiacalix[4]arene phosphine oxides (TCPO) is studied by X-ray photoelectron and emission spectroscopy and quantum chemical methods. The electron density distribution over atoms contained in CPO and ТCPO is analyzed. The structure of higher occupied molecular orbitals (HOMO) is examined. It is shown that HOMOs of these compounds mainly consist of contributions of oxygen 2 p atomic orbitals (AOs) of phosphoryl and hydroxyl moieties and also bridging sulfur 3 p АОs, which indicates the bifunctionality of the considered extractant molecules. The mutual effect of the lower and upper rims of CPOs and ТCPOs as well as the effect of their structures on the electron density distribution over calixarene molecules is investigated

The composition and electronic structure of cadmium sulfide (CdS) nanoparticles formed by the Langmuir-Blodgett (LB) technique on clean silicon wafers and the surface of vertically aligned carbon nanotube (CNT) arrays are studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The samples were annealed in a vacuum at 175 °C and 225 °C to remove the organic matrix of the LB film. From the analysis of the XPS data the increased concentration of sulfate groups on the surface of CdS nanoparticles formed on CNTs and the electron density transfer from CdS to CNTs are determined. An increase in the LB film annealing temperature causes an increase in the degree of crystallinity and the CdS crystallite size and a decrease in the photoluminescence intensity of a CdS-CNT hybrid.

An attempt is made to explain the causes of coloration of LiB₃O₅ crystals after their long-term operation as laser elements. By EPR and optical spectroscopy the impurity and radiation centers are studied in as-grown LiB₃O₅ crystals and in the crystals whose color appeared after the long-term operation as laser elements. In a number of as-grown crystals a copper impurity is detected. EPR spectral parameters and the structural positions of Cu²⁺ ions are found. Defect formation features in electron irradiated as-grown LiB₃O₅ crystals and in the most colored regions of crystals of spent laser elements are analyzed. It is shown that in both growth crystals and crystals after long-term operation as laser elements the same set of radiation defects is observed: oxygen О^- in the interstitial position, an О^- hole center in the crystal structure, and the В²⁺ electron center due to the removal of an oxygen atom near the lithium vacancy. The only distinction is that the concentration of these radiation defects in crystals long used as laser elements is higher than that in growth ones by an order of magnitude. The results obtained enable the conclusion that the cause of coloration of LiB₃O₅ crystals is photo-induced diffusion of lithium atoms and their capture by cation vacancies in the dark part of the crystal, which provides the formation and accumulation of lithium vacancies in the region where the laser beam passes.

Temperature dependences of the electrical conductivity are studied in the range 4.2-300 K and Seebeck coefficient at room temperature of bulk samples of tungsten dichalcogenide polycrystals with niobium substitutions for tungsten and selenium substitutions for sulfur - W_{1- x} Nb _x (S_{1- y} Se _y )₂. The two-dimensionalization of electron transport properties is detected at niobium concentrations x ³ 0.1 in W_{1- x} Nb _x S₂ and x ³ 0.05 in W_{1- x} Nb _x Se₂. In samples with additional partial selenium substitution for sulfur the electron transport remains three-dimensional. At room temperature the Seebeck coefficient (at equal electrical conductivities) is several times higher in the samples with quasi-two- dimensional transport than in the samples with three-dimensional transport. The calculation of the power factor at room temperature shows its nine times increase.

In the paper results of the investigation of the thermal decomposition process of double complex salt [Pt(NH₃)₄][OsCl₆] by x-ray absorption (XAFS) and photoelectron (XPS) spectroscopies have been presented. The data obtained allows a mechanism of the thermal decomposition to be refined. An influence of size effect and nanoalloy formation on chemical shift of Pt and Os is discussed.

The work deals with the establishment of the dependence of the vibrational frequencies of strong O-H^…O and N-H^…O hydrogen bonds for the diagnosing the bonds themselves. To this end, the Raman spectra of a large number of different normal and deutero-substituted crystals characterized by the presence of strong O-H^…O and N-H^…O bonds are measured and the quantum chemical calculation is performed for one of these compounds. The dependence of the O-H stretching frequency on the O^…O distance is constructed differing from that previously known for short O^…O contacts. The mechanisms of significant broadening of the O-H vibration band in strong O-H^…O hydrogen bonds are considered. Different dependences of the N-H vibrational frequencies in N-H^…O bonds are reported and the causes of this diversity are discussed.

Iron(II) dicyanamide and isothiocyanate compounds with 2-(2- tert -butyltetrazol-5-yl)pyridine (L) of the composition [FeL₂(C₂N₃)₂]×2H₂O (I) and [FeL₂(NCS)₂]H₂O (II) are synthesized and studied. The compounds are examined using powder and single crystal XRD (for I), electron (diffuse reflectance spectra) and IR spectroscopy, static magnetic susceptibility. The analysis of the dependence m_eff( Т ) indicates that the exchange interactions of antiferromagnetic nature appear between the iron(II) ions at temperatures below 50 K.

The ¹Н NMR spectra in a binary aqueous triethylamine solution are recorded with a lower critical point of the liquid-liquid phase transition. It is found that, above the critical temperature the ¹Н NMR spectra of water and triethylamine molecules in the phase with a predominant content of triethylamine molecules are characterized by an inhomogeneous broadening. It can be supposed that the found broadening is due to the features of the molecular distribution at the interface.

Impurity-free R BaCo₄O_{7+ x} ( R = Y, Lu) crystals are grown and the evolution of their structure with varying oxygen concentration in the range 0 £ x £ 1.3 is studied. The structural features of the studied samples required to develop an extended strategy of the X-ray crystallographic experiment, which made it possible to obtain more accurate data on unit cell parameters and additional information on the features of superstructure modulation and diffuse scattering, along with the phase composition of crystalline samples. A crystal chemical analysis of the known structural models of R BaCo₄O_{7+ x} is performed and suggestions are made about possible structural changes occurring when the oxygen concentration increases up to the limit.

By means of the mechanical-wave concept of crystal state and the crystallographic analysis the universal regularities of the crystal structure formation are determined: presudotranslational ordering of atoms within unit cells; separate ordering of different groups of atoms with the alignment of their sublattice parameters; the principle of coherent assembly a structure from stable building blocks with the local geometry and block symmetry spread on the structure formed, and so on. The crystallization mechanism is illustrated by specific structures.

The crystallogenesis of three groups of structures of fluoride-orthoborates (and their analogs) with large cations is studied from the point of view of the current cation-framework representations. Their cation frameworks are sterically templated by rigid borate anions and are built as antizeolite structures. Cavities of channel or layered types are filled with components different their composition and configuration with the main function as charge compensators. An example of different functionalities of the identical anions are Ba₃(BO₃)₂ and La₃Ca₃(BO₃)₅ structures. In these structures, two (BO₃) types generate a cation framework, and the third type stabilizes it in ready channels (!).

An approach for the substantiated choice of the indexing procedure of a diffraction pattern is described. The technique is based on a combined use of powder X-ray diffraction data in Bragg-Brentano schemes and 2D GIXD of mainly oriented polycrystalline samples.

The tris-chelate complex of vanadium(IV) (Bu₄N)₂[V(dmit)₃] is prepared from VCl₃ and (Bu₄N)₂[Zn(dmit)₂] (dmit = isotrithionedithiolate C₃S₅^2-) and characterized by single crystal XRD and mass spectrometry. The complex crystallizes in the space group Pna 2₁ and has a distorted octahedral environment of vanadium. The complex is paramagnetic and gives a characteristic EPR spectrum in both solution and solid phase. The g factors and hyperfine interaction constants are determined.

A novel volatile Pt(II)b-iminoketonate complex is synthesized. b-Aminovinylketone H(i-ptac) = [CF₃-C(O)-CH=C(NH₂)-C(CH₃)₃] is used as a ligand. The XRD method is used to determine the structures of the ligand and the complex. The crystallographic data for C₁₆H₂₂F₆N₂O₂Pt are as follows: a = 10.0716(4) Å, b = 10.9572(4) Å, c = 9.6322(4) Å, b = 110.9010(10)°, space group С 2/ m , Z = 2, R = 0.011. The platinum atom has a square planar coordination with two oxygen and two nitrogen atoms of two bidentately linked ketoiminate ligands in trans -position; the PtO₂N₂ coordination site is formed.

Single crystal X-ray diffraction is used to study the nitrosoruthenium mer- trinitrato complex [RuNO(NH₃)₂(NO₃)₃]. The crystallographic data for H₆N₆O₁₀Ru are as follows: a = 7.6477(1) Å, b = 10.8404(2) Å, c = 24.0168(6) Å, a = b = g = 90°, V = 1991.09(7) ų, Z = 8, d _calc = 2/338 g/cm³, space group Р 2₁2₁2₁. The structure is formed of two structurally non-equivalent uncharged mer- [RuNO(NH₃)₂(NO₃)₃] complexes. The complex crystallizes as yellow needles or orange powder belonging to the orthorhombic system. The substance is poorly soluble in water, ethanol, and acetone, stable in dark storage. The comparisons with the EXAFS data for this complex and the theoretical DFT calculations with different functionals are performed.

Volatile iridium(I) complexes [Ir(cod)Cp^x] (Cp^x = pentamethylcyclopentadienyl Cp*, ethylcyclopentadienyl Cp^Et, cod = 1,5-cyclooctadiene) are synthesized and characterized by IR and NMR spectroscopy. The [Ir(cod)Cp*] complex is a solid and the [Ir(cod)Cp^Et] complex is a liquid (SATP). The XRD method is used to determine the structure of the [Ir(cod)Cp*] complex: chemical formula C₁₈H₂₇Ir, space group P2₁/ с , a = 8,4418(2) Å, b = 9,4764(3) Å, c = 19.2682(5) Å, β = 96.128(1) °, V = 1532.61(7) ų, Z = 4, d _calc = 1.888 g/cm³, m = 8.697 mm^-1. The cyclopentadienyl ligand is h⁵-type coordinated; 1,5-cyclooctadiene have a cis - cis conformation and is h⁴-type coordinated. The thermal properties of the complexes are studied by thermogravimetry.

A cluster complex of the composition [CsK₂(m₃-DMF)₂(m-DMF)₃(DMF)₄][{Re₆(m₃-Se)₈}Br₆] is obtained by the reaction of K₄[{Re₆(m₃-Se)₈}(OH)₆]×8H₂O with hydrobromic acid in the presence of CsBr and its subsequent crystallization by diethyl ether diffusion in a dimethylformamide solution. The compound crystallizes in the triclinic space group P , with the following unit cell parameters: a = 13.6169(3) Å, b = 14.7584(4) Å, c = 18.1573(4) Å, a = 103.332(1)°, b = 108.250(1)°, g = 97.371(1)°, V = 3286.55(14) ų, Z = 2, d _calc = 3.130 g/cm³. The crystal structure is built of [{Re₆Se₈}Br₆]^3- anionic cluster complexes and complex [CsK₂(m₃-DMF)₂(m-DMF)₃(DMF)₄]³⁺ cations.

Complexes ZnLCl₂ (I) and [CdLCl₂] _n (IV), where L is chiral bis -pyridine containing fragments of natural monoterpenoide (-)-a-pinene are synthesized. Single crystals of [ZnLCl₂]×CH₂Cl₂ (II), [ZnLCl₂]× i -PrOH (III), and IV compounds are grown. The crystal structures of II and III are composed of mononuclear ZnLCl₂ complex molecules and solvate CH₂Cl₂ and i -PrOH molecules; the coordination polyhedron of the zinc atom Cl₂N₂ is a distorted tetrahedron. According to the single crystal XRD data, complex IV is a 1D coordination polymer; the coordination core CdN₂Cl₄ is a distorted octahedron and Cl atoms are bridging ligands. In the structures of II, III, and IV the L molecule functions as a bidentate chelate ligand. In the solid phase, complexes I and IV exhibit photoluminescence in the visible range (l_max 505 nm and 460 nm respectively). The band intensity in the photoluminescence spectra of I and IV complexes considerably exceeds the band intensity in the spectrum of free L.

Palladium(II) and copper(II) complexes with 2-(2,2-dimethylhydrazone) pentanone-4 are synthesized for the first time. The compounds are characterized by IR and NMR spectroscopy, elemental and single crystal X-ray diffraction analyses. The palladium complex crystallizes in the space group I 4₁/ a ; the copper complex crystallizes in the space group P . Both compounds are molecular; the palladium chelate core has a distorted square geometry and that of copper has a distorted tetrahedral geometry. The average M-O and M-N bond lengths are respectively 1.9808(15) Å and 2.0427(17) Å for M = Pd, 1.915(8) Å and 1.97(1) Å for M = Cu. The chelate O-M-N angles are 88.32(7)-91.67(7)° for M = Pd, 93.37(4)-99.02(5)° for M = Cu.

A gradient chemical structure of micron-sized crystals of CuCrS₂ and CuCr_{1- x} V _x S₂ powders is established by the differential dissolution technique. It is shown that their surface region coherently conjugated with planar faces of CuCrS₂ crystals is enriched with copper whereas the bulk is depleted of copper and the copper sublattice is disordered. A possible mechanism of the formation of surface regions due to a high bulk mobility of copper atoms in the defect copper sublattice is proposed. It is shown that for solid solutions the disordering process involves copper and vanadium atoms and vacancy complexes. The phenomena found are discussed together with the structural and magnetic data.

A low-temperature plasma enhanced chemical vapor deposition procedure is developed for hexagonalого boron nitride nanowalls that are an array of sheets vertically aligned relative to the Si(100) substrate. A triethylaminoborane and ammonia gas phase was used for the first time to form h-BN nanowalls. Nanowall sizes are 50-250 nm long and 10-25 nm thick. Grazing incidence X-ray diffraction and high-resolution transmission electron microscopy techniques are employed to study the structures of boron nitrideх nanowalls. The effect of synthesis parameters (film deposition temperature and growth time) on the chemical and phase compositions, surface morphology, film structure, and their optical properties are analyzed.

FTIR spectroscopy is used to study the distribution of bulk (free) and hydration (bound) water during the extraction of Au(III) and Pt(IV) from acid sulfate-chloride media by reverse micelles consisting of non-ionic (Triton N-42) and anionic (AOT) surfactants. It is shown that the bulk water fraction increases with an increase in the anionic AOT concentration and that of hydration water increases with an increase in the non-ionic Triton N-42 concentration. A decrease in the bulk water fraction and an increase in the hydration water content enhance the extraction capacity of mixed micelles.

Stable colloidal dispersions with a 2 mM TiS₃ concentration (300 mg/l) are obtained by ultrasonic treatment of TiS₃ in acetonitrile and isopropyl alcohol and characterized by physicochemical methods. The electrical double layers for the particles in dispersions are estimated from the measured z-potentials, and the energies of interparticle interactions are calculated based on the Derjaguin-Landau-Verwey-Overbeek theory. The structural and spectroscopic identity of the particles and crystalline TiS₃ is demonstrated for the solid phases obtained from the dispersions.

A comparative study of the structural features of zinc 2,9,16,23-tetra- tert -butylphthalocyanine films (ZnPc( ^t Bu)₄) obtained by vacuum thermal deposition and spin coating techniques is performed. By powder X-ray diffraction, 2D GIXD, and optical absorption spectroscopy it is shown that ZnPc( ^t Bu)₄ films obtained by the spin coating technique consist of a disordered a-phase with small crystallites. After annealing at 200 °C for 3 h the films transform into the b-phase, with crystallite sizes increasing, however, they remain disordered relative to the substrate surface. On heating under the same conditions, the ZnPc( ^t Bu)₄ films obtained by thermal vacuum sublimation transform from the weakly oriented low-temperature a-phase into the oriented b-phase. Dependences of a chemiresistive sensor response of the ZnPc( ^t Bu)₄ films to ammonia (10-50 ppm) are investigated depending on the preparation and annealing methods of the films.

Three new metal-organic coordination polymers (H₂NMe₂)₂[Li₃(btc)(Hbtc)(DMF)₄] (1), [Li₅(DMF)₆(btc)(Hbtc)]×2DMF (2), and [Li₆(DMF)₈(bdc)(Hbtc)] (3) (H₃btc is trimesic acid, H₂bdc is terephthalic acid) are prepared by heating LiOH with different aromatic carboxylic acids in dimethyl formamide (or its mixture with water). The crystal structures and composition of the compounds are determined by single crystal X-ray diffraction. Compound 1 has a layered structure; compounds 2 and 3 have a framework structure.