Structural investigations in the series of spiro(thia)chromans

A comparative assessment was made of the reactivity of carbonyl-containing spirohydrochromans in their reaction with hydrogen sulfide under the conditions of acid catalysis. The special features of the structure of one of the obtained condensed spiro(thia)chromans are examined on the basis of the results from x-ray crystallographic analysis, the¹³C NMR spectra, and quantum-chemical calculations. N. G. Chernyshevskii Saratov State University, Saratov 410026, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1340–1345, October, 1998.     

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 pyrolysed polycarbosilanes

The combination of combustion analysis, IR-spectroscopy and Raman spectroscopy yields information about the chemical state of carbon in polycarbosilanes or silicon carbide. A stable polycarbosilane can be found where carbon is bonded in a network of silicon, carbon and hydrogen. In the temperature range between 700 and 800°C, the polycarbosilane is transformed into an amorphous silicon carbide with a small excess of carbon. During the crystallisation of the amorphous silicon carbide, which takes place at temperatures above 1100°C, glassy carbon is found by Raman-spectroscopy and combustion analysis. Finally after pyrolysis temperatures above 1500°C only silicon carbide exists; this may be caused by the reaction of free carbon with oxygen impurities in the samples.     

Structural investigations of a lead(IV) tetraacetate-pyridine complex

A 1 : 1 crystalline complex of lead(IV) tetraacetate and pyridine (LTA-py) has been prepared. The single-crystal X-ray structure, at 296 and 150 K, establishes the presence of a relatively short Pb-N bond (2.307 A) within an intriguing seven-coordinate lead inner sphere consisting of the pyridine ligand and two bidentate and two monodentate acetate ligands. The pyridine occupies a surprising amount of the available coordination space and has induced a dramatic change in coordination compared to the four chelating acetate ligands found in lead tetraacetate (LTA). Thermal measurements (TGA/DSC) indicate the de-coordination of pyridine and its loss from the solid between 360 and 380 K. (207)Pb CP/MAS NMR spectroscopy also demonstrates the existence of the Pb-N bond through observation of (1)J((207)Pb,(14)N)= 63 Hz and a (207)Pb-(14)N dipolar coupling constant, of 149 Hz. The solid-state (207)Pb NMR parameters are used to give insight into the coordination environment of Pb(iv) in LTA-py. In solution, ligand exchange is rapid on chemical shift and J-coupling time scales. A (207)Pb NMR study of the titration of an LTA solution by pyridine yields a stability constant for LTA-py of K = 1.5 M(-1) and predicts it to have a (207)Pb NMR chemical shift essentially identical to that observed by CP/MAS NMR in the solid state. This correlation between the solid state and solution indicates that the seven-coordinate LTA-py structure found in the crystalline state does persist in solution, and this could further explain why the addition of pyridine has such profound effects on lead(IV) carboxylate-mediated organic reactions. Simulations of exchange-broadened line shapes of (13)C CP/MAS NMR spectra in the temperature regime above 280 K indicate local motion of the pyridine rings in the form of 180 degrees jumps (activation energy 72.5 kJ mol(-1)); these are first such ring flips reported for a coordinated pyridine ligand.     

Structural and conformational investigations in SmA and different SmC phases of new hockey stick-shaped compounds

New meta -substituted homologous three-ring mesogens, the 4-(3-n-decyloxyphenyliminomethyl) phenyl 4-n-alkyloxybenzoates, have been synthesized, which are non-linear due only to the attachment of one of the alkyloxy groups in a meta -position. The mesophases were studied by optical microscopy, differential scanning calorimetry, NMR spectroscopy, X-ray diffraction, and electro-optical and dielectric measurements. Unusual phase behaviour was observed on varying the length of the terminal chain. The most interesting finding is the occurrence of two polymorphic tilted smectic phases designated as SmC₁ and SmC₂. The existence of these phases was revealed by calorimetric studies and also from the pronounced difference in optical textures. It was shown from NMR measurements that the molecular orientation changes from a synclinic to an anticlinic arrangement in the SmC₁ to SmC₂ phase transition. It has also been shown, using NMR, that the SmC₁ → SmC₂ phase transition in these compounds is accompanied by a conformational change in the molecular fragment containing the aromatic ring with the meta-substituted terminal alkyloxy chain. This conformational change is linked to a change in the shape of the molecules and leads to a different packing of the molecules within the layers of the SmC₂ phase. From dielectric measurements an increase by a factor of two was detected in the molecular mobility at the transition into the low temperature SmC₂ phase. This finding supports a change in the packing as result of conformational changes.     

Structural and conformational investigations in SmA and different SmC phases of new hockey stick-shaped compounds

New meta -substituted homologous three-ring mesogens, the 4-(3- n -decyloxyphenyliminomethyl) phenyl 4- n -alkyloxybenzoates, have been synthesized, which are non-linear due only to the attachment of one of the alkyloxy groups in a meta -position. The mesophases were studied by optical microscopy, differential scanning calorimetry, NMR spectroscopy, X-ray diffraction, and electro-optical and dielectric measurements. Unusual phase behaviour was observed on varying the length of the terminal chain. The most interesting finding is the occurrence of two polymorphic tilted smectic phases designated as SmC 1 and SmC 2 . The existence of these phases was revealed by calorimetric studies and also from the pronounced difference in optical textures. It was shown from NMR measurements that the molecular orientation changes from a synclinic to an anticlinic arrangement in the SmC 1 to SmC 2 phase transition. It has also been shown, using NMR, that the SmC 1 →SmC 2 phase transition in these compounds is accompanied by a conformational change in the molecular fragment containing the aromatic ring with the meta -substituted terminal alkyloxy chain. This conformational change is linked to a change in the shape of the molecules and leads to a different packing of the molecules within the layers of the SmC 2 phase. From dielectric measurements an increase by a factor of two was detected in the molecular mobility at the transition into the low temperature SmC 2 phase. This finding supports a change in the packing as result of conformational changes.     

Structural properties of a series of photochromic fluorinated indolylfulgides

Fluorinated indolyl­fulgides are a class of photochromic organic compounds that meet many of the requirements for use as optical memory media and optical switches. The X‐ray crystal structures of a series of five photochromic fluorinated indolyl­fulgides have been determined, namely (3Z)‐3‐[1‐(1,2‐di­methyl‐1H‐indol‐3‐yl)‐2,2,2‐tri­fluoro­ethyl­idene]‐4‐(1‐methyl­ethyl­idene)­dihydrofuran‐2,5‐dione (tri­fluoro­methyl­iso­propyl­idene­indolyl­fulgide), C₁₉H₁₆F₃NO₃, (I), (3Z)‐3‐[1‐(1,2‐dimethyl‐1H‐indol‐3‐yl)‐2,2,3,3,3‐penta­fluoro­propyl­idene]‐4‐(1‐methyl­ethyl­idene)­dihydrofuran‐2,5‐dione (penta­fluoro­ethyl­iso­propyl­idene­indolyl­fulgide), C₂₀H₁₆F₅NO₃, (II), (3Z)‐3‐[1‐(1,2‐di­methyl‐1H‐indol‐3‐yl)‐2,2,3,3,4,4,4‐hepta­fluoro­butyl­idene]‐4‐(1‐methyl­ethyl­idene)­dihydrofuran‐2,5‐dione (hepta­fluoro­propyl­iso­propyl­idene­indolyl­fulgide), C₂₁H₁₆F₇NO₃, (III), (3Z)‐3‐[1‐(1,2‐di­methyl‐1H‐indol‐3‐yl)‐2,2,2‐tri­fluoro­ethyl­idene]‐4‐(tri­cyclo­[3.3.1.1^3,7]­decyl­idene­)dihydrofuran‐2,5‐dione (tri­fluoro­methyl­adamantyl­idene­indolyl­fulgide), C₂₆H₂₄F₃NO₃, (IV), and (3Z)‐3‐[1‐(1,2‐di­methyl‐1H‐indol‐3‐yl)‐2,2,3,3,4,4,4‐hepta­fluoro­butyl­idene]‐4‐(tri­cyclo­[3.3.1.1^3,7]­decyl­idene­)dihydrofuran‐2,5‐dione (hepta­fluoro­propyl­adamantylidenein­dolyl­fulgide), C₂₈H₂₄F₇NO₃, (V). The photochromic property of fulgides is based on the photochemically allowed electrocyclic ring closure of a hexatriene system to form a cyclo­hexa­diene. For each fulgide examined, the bond lengths within the hexatriene system alternate between short and long, as expected. Comparing the structures of the five fulgides with each other demonstrates no significant difference in bond lengths, bond angles or dihedral angles within the hexatriene systems. The distance between the bond‐forming C atoms at each end of the hexatriene system does vary. Correlations of structural properties with optical properties are addressed.     

Structural diversity in a series of alkyl-substituted cesium aryloxides

A family of cesium aryloxides [Cs(OAr)](n) were synthesized and structurally characterized from the reaction of 1:1 or 1:excess stoichiometry of Cs(0) and the appropriate alkyl-substituted phenol: 2-alkylphenol [alkyl = methyl (H-oMP), isopropyl (H-oPP), and tert-butyl (H-oBP)] and 2,6-dialkylphenol [alkyl = methyl (H-DMP), isopropyl (H-DIP), tert-butyl (H-DBP), and phenyl (H-DPhP)]. The products were structurally identified as [Cs(oMP)(H-oMP)(2)](n) (1), [Cs(5)(oPP)(5)](n) (2), [Cs(4)(oBP)(4)(H-oBP)(6)](n) (3x, shown), [Cs(3)(DMP)(3)](n) (4), [Cs(2)(DIP)(2)](n) (5), [Cs(DIP)(H-DIP)](n) (5x), and [Cs(DPhP)](n) (7). Compounds 1-7 were found to adopt complex polymeric structures employing π interactions from the neighboring pendant phenoxide ligands. The solution behavior of these compounds was studied using solution (133)Cs NMR spectroscopy, and for each compound, a single (133)Cs NMR resonance was observed, with chemical shift values found to be strongly solvent-dependent. This implies that monomeric cesium salt species involving solvent interactions exist in solution.     

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 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 landscape on a series of rhein: Berberine cocrystal salt solvates: The formation,dissolution elucidation from experimental and theoretical investigations

The specific crystalline form of a compound remarkably affects its physicochemical properties. Therefore,a detailed analysis of the structural features and intermolecular interactions of a multi-component crystal is feasible to understand the relationships among the structure, physicochemical properties and the formation mechanism. In the present study, three novel cocrystal salt solvates of rhein and berberine were reported for the first time. Various solid characterizations and theoretical com...     

Structural study of a series of layered rare-earth hydroxide sulfates

We report structure analysis of a new family of rare-earth hydroxides Ln(2)(OH)(4)SO(4)·2H(2)O (Ln = Pr, Nd, Sm, Eu, Gd, Tb) from synchrotron X-ray and electron diffraction data. Rietveld profile analysis revealed that all members were isostructural and crystallized in a face-centered monoclinic system A2/m (No. 12), in which the monoclinic angles were approximately equal to the right angle, varying from 90.387(1)° for Pr sample to 90.0718(3)° for Tb sample. The structure consisted of LnO(9) polyhedra connected by μ(3)-hydroxyl groups and μ(2)-water molecules, forming a corrugated two-dimensional layer, which was pillared by bidentated sulfate ions. This series of compounds had a supercell a' = 2a, b' = 2b because of the local orientation ordering of SO(4)(2-). Structural features along the series, such as unit-cell parameters and average Ln-O distances, represented a progressive contraction associated with the shrinking radius of the lanthanide cations from Pr to Tb.     

Structural and dielectric investigations of a binary system of a bi-swallow-tailed and a terminally-polar compound

Induced smectic A phases in binary mixtures of a bi-swallow-tailed component and a second component are described as 'filled smectic A phases', since the second rod-like component is considered to occupy spaces between the terminal branches of the bi-swallow-tailed molecules. A new system of this kind is now described where the second rod-like component has a terminal dipole, thereby enabling dielectric studies of the mixtures. These measurements coupled with calorimetric and X-ray measurements give information about the packing and dynamics of the mixed phases.     

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.     

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.