Structural investigations of alumino-metalloaminocarbene complexes

[Al(NMe₂)₃]₂ combines with Fe(CO)₅ and Mn₂(CO)₁₀ forming bimetallic compounds Fe₂(CO)₈[C(NMe₂)OAl(NMe₂)₂]₂ and Mn₂(CO)₉[C(NMe₂)OAl₂-(NMe₂)₅]. X-ray diffraction analyses reveal the formation of aluminometallocarbene compounds with central connectivities, MC[NMe₂)][OAl(NMe₂)(μ-NMe₂)₂].     

Structural investigations of silicon-rich CVD-SiC

Silicon Carbide (SiC) and Silicon Carbide with free Silicon [SiC(Si)] thin films were prepared by chemical vapor deposition (CVD) using an CH₃SiCl₃-H₂-Ar gas mixture at temperatures of 1173 to 1323 K. The structure of these films were investigated by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The effects of crystallinity, morphology and Si-concentration of the deposits were examinated in some detail.     

Structural investigations of lead-strontium fluoroapatites

Solid solutions in the system Pb_(10−x)Sr_x(PO₄)₆F₂, 0?x?10, were obtained as apatitic phases from aqueous medium. They were investigated by X-ray diffraction, chemical analysis and infrared (IR) spectroscopy. The results of the structural refinements indicated that the substitution of lead by strontium induces a regular decrease of the lattice constant “a” and a preferential strontium distribution in site M(1). A progressive shift of the F⁻ ion position along the apatitic channel was detected and confirmed by IR evidence. The different character of the M-F and M-O interactions was invoked to justify the structural differences observed as a function of composition.     

Structural investigations on 'smectic D' and related mesophases

We have performed time resolved diffraction experiments in order to obtain a better insight upon the metastable phases surrounding some thermotropic mesophases of cubic Ia 3 d and Im 3 m symmetries. These metastable phases are columnar hexagonal, smectic or tetragonal, depending on the nature of the mesogenic molecule. Moreover, it appears that the structure of the cubic phase of the 4-alkyloxybiphenyl-4-carboxylic acids previously labelled smectic D varies with the lateral group substituted on the biphenyl core.     

Structural investigations of enterosorbents based on natural silk

Features of an enterosorbent based on the fibroin of natural silk hydrolyzed in acid and alkaline solutions have been investigated by x-radiographic, electron-microscopic, and sorption methods. It has been shown that, regardless of the pH of the solution, a longitudinal-transverse cleavage of the fibroin of natural silk takes placed on hydrolysis, although in the presence of alkali this process is more intensive than in an acid solution of the same normality.Institute of the Chemistry and Physics of Polymers, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2. pp. 229–233, March–April, 1999.     

Structural investigations on zirconium phosphate-phosphite and on itsn-butylamine intercalate

Zirconium phosphate-phosphite have various structure belonging to the drying heat of the sample. While sample dried above sat. NaCl solution had interlayer distance of 1.30 nm (result fromd ₁=0.74 nm andd ₂=0.56 nm for phosphite layer), the sample dried under IR lamp on air having interlayer spacingd=0.74 nm charactderistic for -Zr(HPO₄)₂·H₂O containing little amount of phosphite groups. The composition of the first sample can be characterized by chemical formula, as Zr(HPO₄)_0.7(HPO₃)_1.3· ·0.5H₂O. The X-ray powder diffraction data ofn-butylamine intercalate suggest that in the process take place only the phosphate region of zirconium phosphate-phosphite (ZrPP).     

Structural investigations under high pressure conditions

Because of its extremely high yield strength, hardness and relatively high transparency to high-energy x-ray radiation, the diamond anvil cell has become a favored device in high pressure research. This includes structural investigations where pressure induced phase transitions can be studied using x-ray diffraction techniques up to several Mbars when combined with a high-brilliance synchrotron source. In this paper several structural studies under high pressure are presented to show general trends. High pressure instrumentation has reached the stage at which hydrogen, according to theoretical calculations, can be metallized and thermodynamic conditions, (i.e. pressure and temperature) exceed those at the center of the earth.     

Structural investigations on polymer latices by small-angle x-ray scattering

An overview is given on recent studies of latices by small-angle x-ray scattering (SAXS). It is demonstrated that SAXS-studies performed at different contrast (contrast variation) allows the full elucidation of the fine structure of the particles down to a size-scale of a few nanometers. Examples are given including studies on core-shell latices composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA) as well as of carboxylated latices.     

Synthesis of functional substituted polycarbosilanes based on silyltriflate derivatives

Polycarbosilanes obtained by the Wurtz method or Grignard synthesis were converted by protodesilylation with trifluoromethanesulfonic acid to triflate-substituted derivatives. Reactions of these polymers with nucleophiles led to novel functionally substituted polycarbosilanes. Polycarbosilanes with a regular alternating arrangement of silicon and carbon atoms, however, could not be obtained by this procedure. Such polymers were prepared by reactions of bis(trifluoromethylsulfonyioxysilyl)methanes with dinucleophiles. All syntheses are characterized by a high regioselectivity and high yields at low temperatures in short reaction times. The structures of the polymers were proven by NMR spectroscopy (²⁹Si, ¹³C, ¹H). © 1995 John Wiley & Sons, Inc.     

Structural investigations of metal clusters by HREM

Silver clusters grown by the inert gas aggregation technique have been investigated by HREM. Undistorted cuboctahedra and icosahedra together with twinned particles have been observed. Three types of nucleation and growth mechanisms are proposed which can explain the observed particle structures. The untwinned large particles are created by the coalescence of liquid- like small clusters. The twins are produced by the coalescence of solid subunits.     

Structural investigations on sodium-lead borophosphate glasses doped with vanadyl ions

Electron paramagnetic resonance (EPR), optical absorption, and FT-IR spectra of vanadyl ions in the sodium-lead borophosphate (Na(2)O-PbO-B(2)O(3)-P(2)O(5)) (SLBP) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO(2+) ions. The spin Hamiltonian parameters g and A are found to be independent of the V(2)O(5) content and temperature. The values of the spin Hamiltonian parameters indicate that the VO(2+) ions in SLBP glasses are present in octahedral sites with tetragonal compression. The population difference between Zeeman levels (N) is calculated as a function of temperature for an SLBP glass sample containing 1.0 mol % VO(2+) ions. From the EPR data, the paramagnetic susceptibility (χ) is calculated at different temperatures, and the Curie constant (C) is calculated from the 1/χ versus T graph. The optical absorption spectra of the glass samples show two absorption bands, and they are attributed to V(3+) and V(4+) ions. The optical band gap energy (E(opt)) and Urbach energy (ΔE) are calculated from their ultraviolet absorption edges. It is observed that, as the vanadium ion concentration increases, E(opt) decreases and ΔE increases. The study of the IR absorption spectrum depicts the presence of BO(3), BO(4), PO(3), PO(4), and VO(5) structural units.     

Structural landscape investigations on bendable plastic crystals of isonicotinamide polymorphs

Three polymorphs (forms I, II and V) of isonicotinamide (INA) were mechanically flexible and exhibited one-dimensional (1D) plasticity. Anisotropic intermolecular interactions contribute to the plasticity of single crystals: weak dispersive interactions between slip planes such as 1D columns in forms I and II or 2D layers in form V were stabilized by strong hydrogen bonds, allowing the layer or column's surface to glide smoothly without hindrance. The disparity of intermolecular interactions on plastic properties of INA polymorphic crystals was confirmed by energy framework analysis, nanoindentation tests and micro-Raman spectroscopy. The crystal which exhibits plastic property provides a promising application in pharmaceuticals and material sciences.     

Structural investigations of isomeric 2,4-diphenyl-7,8-benzohexahydrothiochromenes

Structural investigations were carried out by means of PMR spectroscopy and x-ray diffraction analysis, and the type of fusion of the heterorings and alicyclic rings in isomeric 2,4-diphenyl-7,8-benzohexahydrothiochromenes previously obtained by the disproportionation and ionic and catalytic hydrogenation of 2,4-diphenyl-7,8-benzo-5, 6-dihydrothiochromene was established. The predominant realization of a diastereomer with trans-fused heterorings and alicyclic rings in all of the reactions mentioned above was demonstrated; the possibility of the formation of the eis isomer in the catalytic reduction of benzodihydrothiochromene was confirmed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1060–1063, August, 1980.     

Structural investigations and modeling of cavities in clathrates

Summary A molecular-graphics study has been performed in order to build and visualize the shape of cavities within different clathrates from X-ray diffraction data [e.g. Dianin's compound, Werner complexes Ni(SCN)₂(3-methylpyridine)₄, Fe(acetylacetonate)₃ and Ni(ethylxanthate)₂(4,4-dimethyl-2,2-bipyridyl) complexes]. The algorithm of the solvent-accessible surfaces representation has been applied to a part of the whole crystal structure rather than to isolated host molecules, by using the MOLCAD molecular modeling package. This type of modelization has been found very efficient both to study the shape properties of the host cavities (cage or channel types) and to approach the structural features of the host/guest interactions.     

Structural investigations of the phospholipids of the sunflower

Summary Investigations of the phospholipids of sunflower seeds have been performed which have confirmed the known structures of the phosphatidylcholines and phosphatidylethanolamines. It has been established that the inositophosphatides have the structure of monophosphoinositides. The fatty acid compositions of the individual groups of phospholipids have been studied: they consist mainly of the same selection of acids as the phospholipid complex with the glycerides of the sunflower. The phospholipids form a sequence with respect to increasing saturation: phosphatidylcholines, phosphatidylethanolamines, bis-phosphatidic acids, monophosphoinositides.A solvent system for the identification of the water-soluble products of the acid hydrolysis of phospholipids by chromatography in a thin layer of silica gel has been proposed.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 3–7, January, 1971.     

Analysis of mesophase formation in side-chain liquid crystalline polycarbosilanes

This paper is concerned with an analysis of the thermodynamics and kinetics of mesophase formation by cooling from the isotropic state of side-chain liquid crystalline polycarbosilanes containing spacers in the range from 3 to 11 CH₂-groups. The polymers are characterized by their thermotropic behaviour as far as temperature, enthalpy and entropy of the transitions are concerned. The kinetics was followed by optical and calorimetric methods. Longer spacer length leads to more perfect ordering in the mesophase, higher isotropization temperatures, and lower glass transition temperatures. The Avrami and Ozawa formalism to describe the transition kinetics to the mesophase from the isotropic state cannot be interpreted as the nucleation and growth mechanism known from crystallization.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthday     

Structural and spectroscopic investigations on Eu3+-doped alkali fluoroborate glasses

Eu³⁺-doped alkali fluoroborate glasses B₂O₃–XCO₃–NaF–Eu₂O₃ (where X = Li₂, Na₂, K₂, and Ca, Mg) have been prepared using the conventional melting technique and their structural and optical properties have been evaluated. The XRD pattern of the glasses confirmed the amorphous nature and the FTIR spectra reveal the presence of BO₃ and BO₄ units as their local structures along with the strong OH^? groups. From the absorption spectra the bonding parameters have been calculated and confirmed that the Eu–O bonds in the studied glasses are of covalent nature. Judd–Ofelt (JO) analysis has been carried out from the emission spectra. The JO parameters have been used to calculate transition probabilities (A), lifetime (τ_R) and branching ratios (β_R) and peak stimulated emission cross-section (σ_P^E) for the ⁵D₀ → ⁷F_J (J = 1, 2, 3 and 4) transitions of the Eu³⁺ ions. The decay from the ⁵D₀ level of Eu³⁺ ions in the title glasses has been measured and analysed. The lifetime of the ⁵D₀ level is found to be shorter than the reported glasses which may be due to the presence of OH^? groups.     

Structural investigations on Quinone Methides for understanding their properties in confined media

Encapsulation of 4−[(4′-hydroxy−3′,5′-dimethylphenyl)(aryl)-methylene]−2,6−dimethyl-cyclohexa−2,5−dienones (when aryl=4−hydroxyphenyl 1, 4−methoxyphenyl 2, 2,3,4-trimethoxy phenyl 3) by β-cyclodextrin is studied. The compound 2 is selectively encapsulated by β-cyclodextrin. The result is rationalised by analysing the structural parameters from the crystal structure of 1–3. The visible spectra of the compounds 2 and 3 at pH 9.0 show red shifts on the absorption maxima upon addition of cetyltrimethylammonium bromide (CTAB). For example, addition of a solution of CTAB to aqueous ethanolic solution of 2 at pH 9 causes shift of the absorption at 578–593 nm (Δλ_max=15 nm). The advantage of this observation is taken to use 2 and 3 to determine the critical micelle concentration of CTAB in basic medium.Graphical Abstract Structural investigations on quinone methides for understanding their properties in confined media Rupam J. Sarma, Andrei S. Batsanov, Ritu Kataky, Jubaraj B. Baruah