Equilibrium Structure of Beryllium Dibromide from Combined Gas Electron Diffraction and Vibrational Spectroscopy Analysis

The molecular structure of BeBr₂ has been investigated by gas-phase electron diffraction at the temperature 800(10) K. The conventional analysis yielded the following values: r _g(Be–Br) = 1.944(6)Å, l(Be–Br) = 0.068(4)Å, r _g(Br–Br) = 3.848(8)Å, l(Br–Br) = 0.109(3)Å, k(Be–Br) = 1.1(1.1) × 10^–5 ų, (Br–Br) = 2.1(1.0) × 10^–5 ų. Three models of nuclear dynamics were used to simulate the conventional analysis values—infinitesimal vibrations and two models, which take into account the kinematic and dynamic anharmonicity of the bending vibration. All models give similar values of bond angle, amplitudes, and shrinkage, excluding the harmonic model, which yields too low value l(Br–Br). The equilibrium bond distance r _e(Be–Br) = 1.932(11) Å was estimated, taking into account the anharmonicity corrections for stretching and bending vibrations and centrifugal distortion.     

Synthesis, Structure and Properties of Na2Zn(OEt)4(HOEt)5

The synthesis, structure and properties of Na₂Zn(OEt)₄(HOEt)₅, having the right Na:Zn ratio for sol–gel synthesis of the highly Na-ion conducting ceramic Na_1.8Zn_0.9Si_1.1O₄, is described. It was synthesised in high yield by a metathesis reaction of ZnCl₂ and 4NaOEt in ethanol or ethanol/toluene solvent. The structure was determined by single-crystal X-ray methods and consists of two symmetry related polymeric strands with the metal sequence ...–Zn–Na–Na–Zn–.... Extensive hydrogen bonding is present within each chain. Further characterization was made with IR- and Raman-spectroscopy and thermo-calorimetry, showing that the compound is stable to 65°C.     

The improved synthesis and crystal structure of 20-thiocrown-4

An improved synthesis of 20-thiocrown-4 is reported, which exploits the Kellogg method of cesium carbonate in DMF mediated macrocyclization of precondensed synthones which converge at the cycloicosane structure. The crystal structure of 20-thiocrown-4 reveals a rectangular conformation for the free ligand. Each sulfur is in onegauche and oneanti torsion angle. Four carbon positions make up the corners. There are two short sides comprised of –C–C– torsion angle sequencesg ^–ag^– and two long sides (aaa, g ^–ag⁺). The S–C and C–C bond distances average 1.816(2) and 1.523(3) , respectively. Supplementary data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82147 (9 pages)     

Conformational analysis of fluorinated copolymers of tetrafluoroethylene

Conformational analysis of fluorinated copolymers of tetrafluoroethylene (TFE) is performed by taking into account only intramolecular effects (isolated-chain model). In particular, variations of the chain conformation, which are induced by incorporating different side groups, such as –Cl, –CF₃, –OCF₃, –OCF₂CF₃, and –OCF(CF₃)₂, are investigated and discussed with respect to qualitative correlations between conformation, crystal structure, and supramolecular morphology.     

Core level photoemission spectroscopy and chemical bonding in Sr2Ta2O7

Electronic parameters of constituent element core levels of strontium pyrotantalate (Sr₂Ta₂O₇) were measured with X-ray photoelectron spectroscopy (XPS). The Sr₂Ta₂O₇ powder sample was synthesized using standard solid state method. The valence electron transfer on the formation of the Sr–O and Ta–O bonds was characterized by the binding energy differences between the O 1s and cation core levels, Δ(O–Sr) = BE(O 1s) − BE(Sr 3d_5/2) and Δ(O–Ta) = BE(O 1s) − BE(Ta 4f_7/2). The chemical bonding effects were considered on the basis of our XPS results for Sr₂Ta₂O₇ and earlier published structural and XPS data for other Sr- and Ta-containing oxide compounds. The new data point for Sr₂Ta₂O₇ is consistent with the previously derived relationship for a set of Sr-bearing oxides. The binding energy difference Δ(O–Sr) was found to decrease with increasing bond distance L(Sr–O).     

Molecular and crystalline structure of 2-methyl-4,4-diphenyl-5-phenylazo-2-thia-3-aza-4-phosphahepta-2,4-diene-6-one-2-oxide

The molecular structure of 2-methyl-4,4-diphenyl-5-phenylazo-2-thia-3-aza-4-phosphahepta-2,4-diene-6-one-2-oxide has been determined by x-ray crystallography. The sulfur and phosphorus atoms exhibited distorted tetrahedral coordination. The P-N and P=C bond lengths are intnermediate between single and double bond lengths. Delocalization of -electron density was observed in the flattened molecular fragment Ph–N=N–C(=P)–C(=O)–CH₃.Institute of Physiologically Active Substances, Russian Academy of Sciences, 142432 Chernogolovka. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2737–2741, December, 1992.     

Structural studies on molecular complexes of polyethers. 4 Deoxycholic acid-polyether complexes

Complexes of deoxycholic acid with polyethers, [–(CH₂) _m–1CHR–O–] _n (R=H,m=2–4, 6 andR=CH₃,m=2), were prepared. The crystals are orthorhombic and similar to those most commonly observed for complexes with low molecular weight molecules. Dimensiona in the poly(propylene oxide) complex is about 1 Å longer than those in other polyether complexes, whileb andc do not differ much in these DCA-polyether complexes.     

A screened hybrid density functional study on energetic complexes: Alkaline-earth metal carbohydrazide perchlorates

The molecular geometries, electronic structures and stabilities of a series of alkaline-earth metal carbohydrazide perchlorates were investigated using the Heyd–Scuseria–Ernzerhof (HSE) screened hybrid density functional. The results show that Be and Mg complexes have six-coordinated octahedron features, as previously reported for the transition metal complexes. However, Ca, Sr and Ba complexes have additional coordinated oxygen atoms from the perchlorate ion. Detailed NBO analyses indicate that the metal–ligand interactions are essentially ionic and play an important role in the stabilities of these energetic complexes. The donor–acceptor interactions result in a reduction of occupancies of σ_C=O and σ_N–H bond orbitals, and also their subsequent impact on bond length and bond order.     

Thermally induced early events of ribonuclease A under reducing conditions: Evidenced by principal component analysis and two-dimensional correlation infrared spectroscopy

The thermally induced unfolding of ribonuclease A in the presence of 2-mercaptoethanol has been followed by fluorescence spectroscopy and Fourier transform infrared (FTIR) spectroscopy. Principal component analysis (PCA) in combination with two-dimensional (2D) infrared correlation spectroscopy has been employed as an attractive method for the investigation of subtle pretransitional conformational changes in the protein. Separate analyses of different stages indicated that, in stage I the change of β1(43–49) and α2(24–34) might be the main process; in stage II, β1 was further unfolded, changes of α1(3–13) and another species of β2(61–63) and β4(79–87) involved. Furthermore, quantitative analysis of the power spectra extracted from the synchronous 2D contour maps revealed that the intensity variations from pretransitional stages (below 47 °C) were 5% less than that for the main unfolding. Meanwhile, under reducing conditions the early subtle structural changes occurred in a non-cooperative manner, in contrast to what was found under non-reducing conditions.     

Sol-Gel Synthesis and Structure of Borosilicon Oxycarbide Glasses

Existing sol-gel polymerisation/pyrolysis routes employing two separate boron containing metal alkoxide precursors have been applied to form multi-component silicon oxycarbide glasses based on a borosilicon oxycarbide (B–Si–O–C) system. 29Si, and 11B magic angle spinning nuclear magnetic resonance (MAS-NMR) was used to characterize the atomic structure of the gels, glasses and glass ceramics. Structural changes such as glass formation and crystal nucleation were identified by X-ray diffraction (XRD). Transmission electron microscopy (TEM) provided images of crystal nucleation and growth.     

Rotaxane Type Complexation Behavior of Cyclodextrins with a Series of Donor–Acceptor Covarently Linked Compounds

The complexation behavior of a series of electron donor–accepter (D–A) covalently linked compounds with cyclodextrins (CyDs) has been reviewed. The structure of these complexes showed rotaxane type conformations, which were investigated by means of ¹ H NMR spectrometry. The complex formations induced a fixation of a conformation of guest D–A molecules, and D–A distances were enlarged. Thus, accurate photo-induced charge transfer behaviors can be discussed.     

Elasticity of the crystal-like,amorphous solid-like,and liquid-like structures in deionized suspensions of colloidal silica spheres

Elastic moduli (G) of deionized suspensions of colloidal silica spheres (diameters=45–192 nm; standard deviations of sphere size divided by the mean diameter=0.05–0.21; surface charge densities=0.33–0.94 C/cm²; volume fractions of sphere ()=0.019–0.21) have been determined by the reflection spectrum measurements in a sedimentation equilibrium and the rotatory viscometry. TheG-values are 56–460 Pa (=0.019–0.051), 330–890 Pa (0.06–0.09), and 100 Pa (0.025) for the crystal-like, amorphous solid-like, and liquid-like structures, respectively. TheG-values seem to be in the order amorphous solid-like > crystal-like > liquid-like at the same sphere concentration. The suspension structures and their elastic moduli are highly influenced by the sizes and their monodispersities of the spheres. These results support that the electrostatic intersphere repulsion and the long Debye-screening length around the spheres are important for the appearance of the suspension structures.     

Evolution of the Texture and Structure of SiO2–Al2O3 Xerogels and Aerogels as a Function of the Si to Al Molar Ratio

SiO₂–Al₂O₃ aerogels and xerogels with a Si to Al molar ratio r _Si/Al varying from 0.25 to 20, were made by sol-gel process in acidic conditions at pH 2 and respectively dried by the CO₂ supercritical method and by solvent evaporation. The Al precursor was also chelated with ethylacetoacetate, which made it possible to study the structure and texture of such gels in conditions favorable to the formation of mixed Al–O–Si bonds. Nitrogen adsorption isotherms according to the Brunauer, Emmett and Teller method (BET), ²⁷Al magic angle spinning nuclear magnetic resonance (²⁷Al MAS-NMR), Fourier Transformed Infrared Spectroscopy (FTIR) and Infrared absorbance spectra after Temperature Programmed Desorption (TPD) of pyridine, showed that the Si–O infrared asymmetric stretching vibration and the Bronsted acidity relative to the Lewis acidity, depended on the ratio of Al^IV to Si atoms.     

Arcutin — A new type of diterpene alkaloids

The structure of the diterpene alkaloid arcutin, which is isolated fromAconitum arcuatum Maxim. (Ranunculaceae), is solved by x-ray methods. Arcutin represents a new type of diterpene alkaloids containing a C5–C20 bond instead of the traditional C10–C20 bond in the carbon backbone.Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 62–65, January–February, 2000.     

Effect of Hydration–Dehydration Processes on the Structure and Porosity of Detemplated Silica Fibers

A study was carried out on the conditions of template removal (calcination or extraction by solvents) and hydration–dehydration processes on the hexagonal structure and porosity of detemplated fibers. The hydration–dehydration cycle leads to a decrease in fiber porosity, especially in fiber detemplation by extraction with surfactant solvents such as ethanol and acetic acid.     

Nb28Ni33.5Sb12.5, a New Representative of the X-phase

The first ternary compound in the Nb–Ni–Sb system, Nb₂₈Ni_33.5Sb_12.5, has been synthesized and its structure has been determined by single-crystal X-ray diffraction methods. Nb₂₈Ni_33.5(2)Sb_12.5(2) adopts the X-phase structure type (orthorhombic, space group Pnnm, Z=1, a=13.2334(5) Å, b=16.5065(7) Å, c=5.0337(2) Å), which belongs to the set of tetrahedrally close-packed (TCP) structures adopted by many intermetallic compounds. Typical of such TCP structures, the atoms reside in sites of high coordination number, with Ni and Sb in CN12 and Nb in CN14, -15, and -16 sites. The relative importance of various metal–metal bonding interactions is discussed on the basis of extended Hückel band structure calculations. Nb₂₈Ni_33.5Sb_12.5 displays metallic behavior with a room-temperature resistivity of 2.3×10⁻⁴ Ω cm.     

Structures of Concentrated Sulfuric Acid Determined from Density, Conductivity, Viscosity, and Raman Spectroscopic Data

Addition of water to stoichiometric 100% sulfuric acid increases the density untila maximum results near 87 mole% H₂SO₄. The density and conductivity maximaand viscosity minimum, the latter two near 75 mole%, are direct macroscopicresponses to microscopic quantum mechanical properties of H₃O⁺ and of nearlysymmetric H-bond double-well potentials, as follows: (1) lack of H bonding tothe O atom of H₃O⁺; (2) short, 2.4–2.6 A, O—O distances of nearly symmetricH bonds; and, (3) increased mobility of protons in such short H bonds, give riseto the density maximum via (1) and (2); (1) produces the viscosity minimum;and the conductivity maximum results from (2) and (3). A pronounced minimumnear 1030 cm^–1 in the symmetric SO₃ stretching Raman frequency of HSO₄ ^–,observed near 45 mole% also results from double-well effects involving the shortH bonds of direct hydronium ion—bisulfate ion pair interactions. Estimates of theconcentrations of the (H₃O⁺)(HSO₄ ^–) and (H₂SO₄)(HSO₄ ^–) pair interactions weredetermined from Raman intensity data and are given for compositions between42–100 mole%     

Toward the Experimental Structure Determination of Larger Molecular Clusters: Application and Limitations of the Weak Interaction Model to the (C6H6)13B2u ← A1g00 0 Spectrum

The experimental B_2u A_1g0⁰ ₀ spectrum of (C₆H₆)₁₃ was analyzed within the weak-interaction model using minimum energy structures calculated from six different potential energy surfaces. The coexistence of two isomers—both of C₃ symmetry and with nearly equal populations—is supported. Structures predicted by two of the six potential energy surfaces are strongly favored. The transition dipole of benzene moieties within the cluster has a magnitude of 0.23 Debye. Weak transition dipole–dipole interactions fall between –1.95 and +2.24cm^–1 and site shifts of ligand molecules range from –160.3 to –153.8cm^–1. Although the weak-interaction transition dipole–dipole model falls short of unambiguously determining isomeric structures of benzene-13, it establishes a solid foundation on which modeling can be based for determining structures of larger, high-symmetry, molecular clusters.     

Vibrational spectra of 2-biphenylmethanol. Spectrum simulation and molecular structure

The vibrational spectra of a solid crystalline sample of 2-biphenylmethanol have been measured at room temperature. The IR absorption spectra were recorded in the range 400 cm^–1–3600 cm^–1; Raman spectra were measured in the range 10 cm^–1–1640 cm^–1. The direct mechanical and optoelectronic problems were solved using the fragment method realized as Lev-100 software; the intensity distribution in the IR spectrum of 2-biphenylmethanol was obtained by the same method. The experimental Raman and IR absorption spectra were interpreted by analyzing the calculated data on the frequencies and forms of normal vibrations and their intensities in the IR spectra. IR absorption spectra were simulated for several models of 2-biphenylmethanol conformers that differ in the mutual orientation of fragments. Based on the results of simulation and comparison of the calculated and experimental spectra of conformers we suggested a model for the conformer realized in the solid phase under normal conditions.Original Russian Text Copyright © 2004 by L. M. Babkov, J. Baran, N. A. Davydova, J. I. Kukielskii, and S. V. TrukhachevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 624–631, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Effect of nanobubbles on friction forces between hydrophobic surfaces in water

Micro- and nanoscale combined hierarchical polymer structures were fabricated by UV-assisted capillary force lithography. The method is based on the sequential application of engraved polymer molds with a UV-curable resin of polyurethane acrylate (PUA) followed by surface treatment with a trichloro(1H,1H,2H,2H-perfluorooctyl) silane in vapor phase. Two distinct wetting states were observed on these dual-roughness structures. One is “Cassie–Wenzel state” where a water droplet forms heterogeneous contact with microstructures and homogeneous contact with nanostructures. The other is “Cassie–Cassie state” where a droplet makes heterogeneous contact both with micro- and nanostructures. A simple thermodynamic model was developed to explain static contact angle, hysteresis, and wetting transition on dual-roughness structures.