Stretching vibrations and structure of (HF) n (n=4–8) clusters

IR spectra of 24 structural isomers of (HF) _n (n=4–8) clusters were calculated in the framework of semiempirical theory of polyatomic molecule vibrations. Based on the results obtained and available experimental data it is proposed that (HF) _n associates comprising 3–5-membered cycles with attached monomeric HF units are present in molecular beams and gas phase.Ab initio calculations performed by the SCF method show the existence of local minima corresponding to such structures on the potential energy surface of (HF) _n clusters (n=4–6). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 435–443, March, 1997.     

Microstructure and surface composition of corn starch cryogels with sorbed organic flavoring agents

The surface composition and surface microtopography of corn starch cryogels obtained from a 3% starch sol containing organic flavoring agents were studied by X-ray photoelectron spectroscopy and scanning electron microscopy. The cryogels withn-octanol,n-octyl methyl ketone, andn-octyl acetate have a well-developed microtopography and their surface layer (5–20 nm) is enriched in sorbed compounds.n-Octyl acetate, unliken-butyl acetate, influences the composition and microstructure of the cryogel surface. The sorbedn-octyl acetate occupies 20–25% of the surface, which has a well-developed topography and a porous structure. Drying and evacuation do not change the concentration of the organic sorbates having a C₈ alkyl group in the surface layer. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 312–314, February 2000.     

Effect of the nature of zeolite and modifying additives on the activity of zeolite-containing catalysts inn-butane isomerization

Isomerization ofn-butane on various types of zeolites (ZVM, ZVK, mordenite, and Y) modified with transition metals and cationic and anionic additives was investigated. Under the conditions studied, H-forms of zeolites are inactive. Pt-containing systems based on the H-form of ZVM (HZVM) are the most efficient catalysts forn-butane isomerization, and the yield of isobutane reaches 20–26 wt.% at a selectivity of 40–45%. Modification of this catalyst with Ga and Fe compounds or with an aqueous solution of HCl increases the selectivity with respect to isobutane up to 70–90%. Introduction of Zn²⁺ cations or F⁻ and SO₄ ²⁻ anions into the Pt-containing HZVM system decreases the selectivity and yield of isobutane due to the formation of very strong acidic centers on which disproportionation and hydrocracking ofn-butane mainly occur. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1281–1285, July, 1999.     

Kinetics of heat release during the reaction ofn-decane with nitrogen dioxide in the liquid phase

The rates of heat release in the nitrogen dioxide—n-decane system at a molar ratio of nitrogen oxides ton-decane (β) from 2.4·10⁻³ to 3.1 and gaseous volumes per mole ofn-decane (V(g)) equal to 0.05–4.5 were studied in the 55.2–92.8 °C temperature range. The initial rate of the process is determined by the interaction of NO₂ withn-decane. The equilibrium constants of dissociation of N₂O₄ inn-decane and Henry's constants of NO₂ and N₂O₄ in ann-decane solution were determined by complex analysis of the thermodynamic equilibrium in the NO₂—n-decane system and dependences of the initial rates onV(g) and β. The experimentally observed self-acceleration of the process in the region of high β and lowT values was suggested to be due to the reaction of N₂O₄ with intermediate oxidation products. The rate constants of the reaction of NO₂ withn-decane were compared with analogous values determined in its mixtures with HNO₃ solutions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1789–1794, October, 1997.     

Structural studies of five layer Aurivillius oxides: A2Bi4Ti5O18 (A=Ca, Sr, Ba and Pb)

The room temperature structures of the five layer Aurivillius phases A₂Bi₄Ti₅O₁₈ (A=Ca, Sr, Ba and Pb) have been refined from powder neutron diffraction data using the Rietveld method. The structures consist of [Bi₂O₂]²⁺ layers interleaved with perovskite-like [A₂Bi₂Ti₅O₁₆]²⁻ blocks. The structures were refined in the orthorhombic space group B2eb (SG. No. 41), Z=4, and the unit cell parameters of the oxides are a=5.4251(2), b=5.4034(1), c=48.486(1); a=5.4650(2), b=5.4625(3), c=48.852(1); a=5.4988(3), b=5.4980(4), c=50.352(1); a=5.4701(2), b=5.4577(2), c=49.643(1) for A=Ca, Sr, Ba and Pb, respectively. The structural features of the compounds were found similar to n=2-4 layers bismuth oxides. The strain caused by mismatch of cell parameter requirements for the [Bi₂O₂]²⁺ layers and perovskite-like [A₂Bi₂Ti₅O₁₆]²⁻ blocks were relieved by tilting of the TiO₆ octahedra. Variable temperature synchrotron X-ray studies for Ca and Pb compounds showed that the orthorhombic structure persisted up to 675 and 475 K, respectively. Raman spectra of the compounds are also presented.     

不同硅铝比Cu-ZSM-5纳米片上N2O催化分解

以双季铵盐表面活性剂为模板剂,水热条件下合成了硅铝比(nSi/nAl)为18、26和95的ZSM-5沸石纳米片,采用离子交换方法制备了铜改性的ZSM-5纳米片样品,并测试了其催化分解N_2O性能。结合X射线衍射(XRD)、N_2吸附/脱附、X射线荧光光谱(XRF)、扫描电镜(SEM)、透射电镜(TEM)、氢气程序升温还原(H_2-TPR)、氧气程序升温脱附(O_2-TPD)和原位红外漫反射光谱(CODRIFT)等表征结果 ,探讨了沸石硅铝比对于催化剂N_2O分解性能的影响及其原因。结果表明,ZSM-5纳米片硅铝比越低,CuZSM-5纳米片催化剂的活性越高。催化活性的提高归因于低硅铝比催化剂上Cu~+活性物种可还原性的增强和吸附氧脱附能力的提高。     

螺桨烷型分子BX[(CH_2)_n]_3和BX(CH_2)[CH(CH_2)_nCH](X=N,P)的结构和性质

采用密度泛函理论(DFT)研究了螺桨烷型分子BX[(CH2)n]3和BX(CH2)[CH(CH2)n CH](X=N,P;n=1-6)的结构、稳定性、化学键和电子光谱性质.计算结果表明这些分子都是稳定的.BX[(CH2)n]3(X=N,P;n=1-6)的最高占据分子轨道(HOMO)和最低空分子轨道(LUMO)之间的能隙均大于5.20 eV,其中BN[CH2]3和BP[CH2]3的能隙超过7.0 eV,与C5H6的能隙(7.27 eV)很接近,BX(CH2)[CH(CH2)n CH](X=N,P;n=1-6)的能隙在6.80 eV左右.所研究分子能量的二阶差分表明BN[(CH2)3]3、BP[(CH2)4]3及BX(CH2)[CH(CH2)2CH](X=N,P)是最稳定的.BX[(CH2)n]3的Wiberg键级表明除了BN[(CH2)n]3(n=2和6)中不存在B―N键,其它化合物中B和N均形成了化学键,BP[(CH2)n]3中除了BP[(CH2)2]3不存在B―P键,其它的均存在.电子密度的拓扑分析表明N―B键属于离子键,而P―B键具有共价键特征.BX[(CH2)n]3(X=N,P)的第一垂直激发能分别在191.1-284.8 nm和191.8-270.1 nm之间,BX(CH2)[CH(CH2)n CH](X=N,P)的第一垂直激发能分别在190.5-199.7 nm和209.0-221.3 nm之间.     

N-(n-Alkyl)-N′-diphenylphosphorylureas as a new type of extractants for preconcentration of actinides and lanthanides

N-(n-Alkyl)-N′-diphenylphosphorylureas Ph₂P(O)NHC(O)NHC _n H_2n+1 (n = 6–10) were synthesized by the reaction of diphenylphosphoryl isocyanate with primary n-alkylamines C _n H_2n+1NH₂. The products (especially N-diphenylphosphoryl-N′-n-octylurea) are efficient extractants capable of extracting actinides and lanthanides from nitric acid solutions with high distribution coefficients. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 374–379, February, 2008.     

Chemistry of superacids

Superelectrophilic nitration of deactivated aromatics with NO₂Cl−3MX _n complexes in aprotic nonpolar solvents such as CH₂Cl₂ makes it possible to obtain the corresponding nitro derivatives in good to almost quantitative yields under mild conditions. For part 34, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 953–956, May, 1998.     

Theoretical Investigations of the Effect of a Homologous Series of Anionic Surfactants on the Metabolism Bioactivity of Chromobacterium violaceum

Theoretical calculations were performed to obtain physicochemical properties associated with the effect of homologous anionic n-alkylsulfate surfactants on the metabolism of Chromobacterium violaceum. The quantitative experimental effects on the respiration process were those obtained from calorimetric data and were used to correlate the Structure–Activity–Relationship (SAR) of these compounds. Semiempirical AM1 and ab initio DFT levels, employing the set CEP-31G, were used for the theoretical calculations and were parameterized using the continuum-solvation model COSMO for solvent contributions. Chemometric analyses (HCA: hierarchical cluster analysis and PCA: principal component analysis) were used to correlate the physicochemical properties of these compounds and their biological activities. The results indicate that the biological activities of these compounds increase as the hydrocarbon chain length, volume, molar volume and exothermic enthalpy of formation (Δ_f H ^∘) increase; in contrast they decrease with decreases of the solvent effect (SE), ionization enthalpy (IE) and HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies.     

Non Aqueous Titration and Catalytic Conversion of Cyclohexanol as a Test of Surface Acidity

Summary. The textural characteristics, including surface area, mean pore diameters, and total pore volume of Cr₂O₃–CuO/Al₂O₃ solid catalysts were determined from the low temperature adsorption of N₂ at 77 K. The structural properties were investigated using XRD. The surface acidity of calcined samples was determined using two comparable methods, including the non-aqueous titration of acidic groups with n-butylamine and dehydration/dehydrogenation activity of cyclohexanol. XRD patterns assigned a crystalline CuO and γ-Al₂O₃ for 723 K calcinations products of lower Cr₂O₃ content. The gradual increase of calcinations temperature promoted the crystallinity of Cr₂O₃ and resulted in solid–solid interaction of CuO and Cr₂O₃ forming CuCr₂O₄. The textural parameters varied with both calcinations temperature and catalyst composition. The surface acid density (DAS) increased with the increase of chromia content up to 0.132 mole% Cr₂O₃, while the rise of calcinations temperature led to a decrease of surface acidity. The dehydration/dehydrogenation of cyclohexanol as well as n-butylamine titration succeeded in characterizing of surface acidity. Present address: Chemistry Department, College of Science, King Faisal University, Al-Hofuf 31982, Saudi Arabia     

Synthesis and characterization of n=5, 6 members of the La4Srn−4TinO3n+2 series with layered structure based upon perovskite

Layered compounds have been synthesized and structurally characterized for the n=5 and 6 members of the perovskite-related family La₄Sr_n−4Ti_nO_3n+2 by combining X-ray diffraction and transmission electron microscopy. Their structure can be regarded as comprising [(La,Sr)₅Ti₅O₁₇] and [(La,Sr)₆Ti₆O₂₀] perovskite blocks joined by crystallographic shears along the a-axis, with consecutive blocks shifted by 1/2 [100]_p. The n=5 member is similar to the previously reported n=5 member of other A_nB_nO_3n+2-related series. The n=6 member, which has only been briefly reported in other systems previously, is also a well-behaved member of this A_nB_nO_3n+2 series.     

Hydrosilylation of fullerence C60

The hydrosilylation of C₆₀ by diphenylsilane was studied. Silicon-containing derivatives C₆₀H _n (HSiPh₂) _n (n=2, 4, 6) were obtained. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1697–1699, September, 1997.     

Gas-chromatographic method of evaluation ofn-alkanol ability for self-association in pure liquid

The values of the gas-chromatographic indicator reflecting the capacity of analytes for self-association in pure liquids, δT _b.p., were estimated for C₁–C₉ and C₁₁ n-alkanols by capillary gas chromatography on a nonpolar stationary phase under isothermal conditions. The δT _b.p. values ofn-alkanols, found as the difference between the boiling points measured directly and those calculated from GC data, are correlated with thermodynamic characteristics of the formation ofn-alkanol associates in pure liquids. Usingn-alkanols as analytes with insignificant temperature increments of the retention indices, it was shown that the δT _b.p. values can be determined under conditions used in gas chromatography with temperature programming. In this way a single chromatographic run can be used to compare the capacities for self-association of analytes boiling over a wide temperature range. The C₂–C₉ n-alkanethiols, which are not associated in neat liquids, have negative δT _b.p. values. An interpretation of this finding is proposed. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 315–318 February, 2000.     

Phase Transformations in Formation of Layered Perovskites from Coprecipitated Components

We have determined the characteristic features of formation of layered perovskite-like compounds of the type A _n B _n O_3n+2 (n = 5, 6) from systems of coprecipitated hydroxides or hydroxocarbonates. We have established that the process of formation of the crystalline five-layer or six-layer perovskite-like structure of compounds of the A _n B _n O_3n+2 type occurs only according to a two-step mechanism.     

Formation and Characterization of Large (Ar) n , (N2) n , and Mixed (Ar) n (N2) m van der Waals Clusters Produced by Supersonic Expansion

This paper reports the formation and characterization of large (Ar) _n , (N₂) _n , and mixed binary (Ar) _n (N₂) _m van der Waals clusters produced at room temperature in the process of supersonic expansion. The average cluster size is determined by the buffer gas induced beam-broadening technique. For both Ar and N₂ clusters, power variations of the average cluster size with the gas stagnation pressure P ₀ give size scaling as . The average cluster sizes of argon vary from 2950 to more than 30900 atoms per cluster with the argon gas stagnation pressures ranging from 4 to 14 bars, and of nitrogen vary from 600 to more than 10400 molecules per cluster with the nitrogen gas stagnation pressures ranging from 8 to 38 bars. The mixed binary (Ar) _n (N₂) _m cluster is produced by supersonic expansion of an Ar–N₂ mixture. The large mixed binary (Ar) _n (N₂) _m clusters with the average sizes n + m between 1000 and 16000 are obtained. In coexpansion of Ar–N₂ mixture, we find that the argon concentration becomes higher in the beam than before the expansion. This finding is discussed and may be helpful for further insight into the phenomenon of clustering.     

A theoretical study of explosive sensitizers

Quantum chemical calculations at the HF/6-31G^* and B3LYP/6-31G^* levels have been performed on five explosive sensitizers, ethyl nitrate (EN), n-propyl nitrate (NPN), isopropyl nitrate (IPN), 2-ethylhexyl nitrate (EHN) and tetraethylene glycol dinitrate (TEGDN). Theoretical study has made a detailed molecular-level investigation of the title compounds. Based on the Mulliken populations and bond lengths, the fission of the O₂–N₃ can be acceptable reasonably. Charge distribution analysis indicates that the five nitrates produce NO₂ gas during the dissociation of the O₂–N₃ weak bond. We also order the relative thermal stability of five nitrates on the basis of frontier orbital energy (E _HOMO, E _LUMO) and energy gap (ΔE = E _HOMO − E _LUMO).     

Synthesis and characterization of spinel-type CuAl<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocrystalline by modified sol–gel method

Nanocrystalline Copper aluminate (CuAl₂O₄) was prepared by sol–gel technique using aluminum nitrate, copper nitrate, diethylene glycol monoethyl ether and citric acid were used as precursor materials. This method starts from of the precursor complex, and involves formation of homogeneous solid intermediates, reducing atomic diffusion processes during thermal treatment. The formation of pure crystallized CuAl₂O₄ nanocrystals occurred when the precursor was heat-treated at 600 °C in air for 2 h. The stages of the formation of CuAl₂O₄, as well as the characterization of the resulting compounds were done using thermo–gravimetric analysis, X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The products were analyzed by transmission electron microscopy and ultraviolet–visible (UV–Vis) spectroscopy to be round, about 17–26 nm in size and E _g = 2.10 eV.     

Thick Fe2O3, Fe3O4 films prepared by the chemical solution deposition method

Fe₂O₃, Fe₃O₄ films have been prepared from Fe(OCH₂CH(CH₃)₂)₃–(CH₃)₂CHCH₂OH–2.2′-diethanola- mine (DEA)–poly(vinylpyrrolidone) (PVP) solutions by the spin-(SC) and dip-coating (DC) technique on SiO₂ and Si substrates. The maximum film thickness achieved without crack formation has been increased by incorporation of PVP (relative molecular weights 40000 and 360000) into the precursor solution. The stability of the precursor solutions was remarkably increased by addition of DEA. Compact, dense, and crack-free Fe₂O₃ films with thicknesses 900 nm (DC), 450 nm (SC), have been obtained via single-step deposition cycle. Higher-molecular-weight PVP has been more effective in increasing the thickness. The minimum concentration of DEA, which results in pronounced increase of solutions stability, is about R _P (n(DEA)/n(Fe) = 0.1). The high content of carboneous residue in the pyrolysed Fe₂O₃ films promotes the formation of Fe₃O₄ films via reduction in a gas flow of H₂/N₂ gas mixture. Microstructure, surface morphology, and magnetic properties of the films have been also investigated using SEM, AFM, and SQUID, respectively.     

Thermotropic Liquid Crystals of Double-Chain Zwit-terionic Surfactants (C16)2NCnS

A series of double-chain sulfobetain zwitterionic surfactants with varying carbon number of the intercharge group (spacer), (C₁₆H₃₃)₂NCH₃(CH₂)_nSO₃, where n=2, 3, 4, and 6, referred to as (C₁₆)₂NC_nS, were synthesized. The influence of the spacer length on the thermal behaviors of (C₁₆)₂NC_nS in their pure state was studied using thermogravimetry (TG), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD). Thermogravimetric analysis (TGA) showed that the thermal stability of (C₁₆)₂NC_nS lowered with increasing the spacer length. All compounds showed a complex polymorphism. Only for (C₁₆)₂NC₄S and (C₁₆)₂NC₆S, thermotropic liquid crystals were observed using POM. The former exhibited a smectic A (SmA) phase, whereas the latter formed a hexagonal columnar phase. These liquid crystals obtained both in the cooling and the second heating scans provided compelling evidence for the thermal stability of these compounds.