Fabrication and Characterization of Sol-Gel Derived Potassium Sodium Strontium Barium Niobate

Potassium sodium strontium barium niobate (K_0.2Na_0.2Sr_0.48Ba_0.32Nb₂O₆, KNSBN) powder and thin films dip coated onto Si(100) substrates have been prepared by sol-gel route. The thermal evolution of these sol-gel derived KNSBN was studied by differential thermal analysis (DTA) and thermogravimetry (TG). Their structural changes at different annealing temperatures were examined by X-ray diffraction (XRD) and Raman spectroscopy. Our results suggest that the KNSBN tetragonal tungsten bronze (TTB) phase is formed via an intermediate orthorhombic phase. Pure TTB phase KNSBN was obtained at annealing temperatures of 1200°C and 600°C for powder and films respectively.     

Sulfur Compounds. 164 Thermal Polymerization of the Cyclic Seleniumsulfide 1,2-Se2S5 Studied by DSC,HPLC, Raman Spectroscopy,and X-Ray Diffraction

Solid 1,2-Se₂S₅ polymerizes endothermically at 47°C to give a linear polymer which after stretching and extraction consists of helical molecules similar to those of polymeric sulfur. Heating of the polymer results in slow exothermic depolymerization at 84°C to give a mixture of seven cyclic Se_nS_8–n molecules which melts at 111°C. When the polymeric Se₂S₅ is refluxed with CS₂ the initial depolymerization Products are 1,2-Se₂S₅, SeS₅ and 1,2,3-Se₃S₅ but in addition SeS₇ and 1,2-Se₂S₆ are formed. These results indicate the atomic sequence –Se? S₅? Se– in the polymer. The powder x-ray diffraction pattern and Raman spectrum of the polymer as well as its lattice parameters are reported and the Probable mechanism of its depolymerization is discussed.     

The Glaserite-like Structure of Double Sodium and Iron Phosphate Na3Fe(PO4)2

The double sodium and iron phosphate Na₃Fe(PO₄)₂ was synthesized and studied by the XRD method, the second harmonic generation technique, and Mössbauer and IR spectroscopy. The compound crystallizes into a monoclinic system (space group C2/c) with unit cell parameters a=9.0736(2) Å, b=5.0344(1) Å, c=13.8732(3) Å, β=91.435(2)° and is found to be related to the K₃Na(SO₄)₂ structure type. The crystal structure was determined by Rietveld analysis (R_wp=5.86, R_I=2.03). Iron cations occupy the M (Na) position while sodium cations occupy the X (K) and Y (K) positions of the glaserite-like structure. Mössbauer spectroscopy shows the presence of high-spin Fe³⁺ in octahedral coordination.     

tudy on compatibility of imatinib mesylate with pharmaceutical excipients

Differential scanning calorimetry and thermogravimetric analysis with the support of X-ray powder diffraction and infrared spectroscopy were used as screening techniques for the compatibility testing of imatinib mesylate, with following excipients: magnesium stearate, polyvinylpyrrolidone, microcrystalline cellulose. In order to maximize the probability of interactions 1:1 (by mass) drug: excipient binary mixtures were analysed and compared to individual components. Additionally an influence of storage at temperatures of 25 and 40°C on physico-chemical stability on drug – excipient binary mixtures was investigated. The largest visible changes were observed in the DSC curves of imatinib mesylate – magnesium stearate mixtures.     

The crystal polymorphs of metazachlor

Five crystal polymorphs of the herbicide metazachlor (MTZC) were characterized by means of hot stage microscopy, differential scanning calorimetry, IR- and Raman spectroscopy as well as X-ray powder diffractometry. Modification (mod.) I, II and III° can be crystallized from solvents and the melt, respectively, whereas the unstable mod. IV and V crystallize exclusively from the super-cooled melt. Based on the results of thermal analysis and solvent mediated transformation studies, the thermodynamic relationships among the polymorphic phases of metazachlor were evaluated and displayed in a semi-schematic energy/temperature-diagram. At room temperature, mod. III° (T _fus =76°C, Δ_fus H _III =26.6 kJ mol^-1) is the thermodynamically stable form, followed by mod. II (T _fus =80°C, Δ_fus H _II =23.0 kJ mol^-1) and mod. I (T _fus =83°C, Δ_fus H _II=19.7 kJ mol^-1). These forms are enantiotropically related showing thermodynamic transition points at ~55°C (T _{trs, III/II}), ~60°C (T _{trs, III/I}) and ~63°C (T _{trs, II/I}). Thus mod. I is the thermodynamically stable form above 63°C, mod. III° below 55°C and mod. II in a small window between these temperatures. Mod. IV (T _fus =72-74°C, Δ_fus H _II =18.7 kJ mol^-1) and mod. V (T _fus =65°C) are monotropically related to each other as well as to all other forms. The metastable mod. I and II show a high kinetic stability. They crystallize from solvents, and thus these forms can be present in commercial samples. Since metazachlor is used as an aqueous suspension, the use of the metastable forms is not advisable because of a potential transformation to mod. III°. This may result in problematic formulations, due to caking and aggregation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vibrational study of tamoxifen citrate polymorphism

The trans isomer of (Z)-2-[p-(1,2-diphenyl-butenyl)phenoxy]-N,N-dimethyletylamine (tamoxifen) is well known for its endocrine activity as an antiestrogenic agent. Its citrate salt, a widely used pharmaceutical agent, appears in three main polymorphic forms, two of which are well known (I and II) and another form not yet well evidenced.

A vibrational study has been conducted for identifying the two known polymorphic forms of tamoxifen citrate (I and II) and for characterising the other form (form III) examined in this study.

Other techniques for the characterization of the different polymorphs, such as XRDP, have been used.     

Understanding the Origins of Nucleophilic Hydride Reactivity of a Sodium Hydride–Iodide Composite

Sodium hydride (NaH) has been commonly used as a Brønsted base in chemical syntheses, while it has rarely been employed to add hydride (H^?) to unsaturated electrophiles. We previously developed a procedure to activate NaH through the addition of a soluble iodide source and found that the new NaH–NaI composite can effect even stereoselective nucleophilic hydride reductions of nitriles, imines, and carbonyl compounds. In this work, we report that mixing NaH with NaI or LiI in tetrahydrofuran (THF) as a solvent provides a new inorganic composite, which consists of NaI interspersed with activated NaH, as revealed by powder X‐ray diffraction, and both solid‐state NMR and X‐ray photoelectron spectroscopies. DFT calculations imply that this remarkably simple inorganic composite, which is comprised of NaH and NaI, gains nucleophilic hydridic character similar to covalent hydrides, resulting in unprecedented and unique hydride donor chemical reactivity.     

Synthesis,crystal structure,vibrational and dielectric properties of di-benzyl-ammonium selenite monohydrate

The new hybrid compound [C₆H₅CH₂NH₃]_2·SeO_3·H₂O was synthesized and found to crystallize in the triclinic space group P$\overline{1}$. This structure can be described as an alternation between organic and inorganic chains connected by two types of N−HO and O−HO hydrogen bonds. The two and antiparallel cations [C₆H₅CH₂NH₃]⁺are arranged in a face-to-face pattern with a distance of 3.911(10)Å between them, indicating the existence of π-π interaction. The thermal properties show that the mass losses take place in three steps, which correspond to dehydration and degradation of the title compound. The IR and Raman spectra prove the existence and independence of the organic and inorganic groups as well as a water molecule. The equivalent circuit is modeled by a combination series of two parallel R–CPE circuits. Dielectric studies show that this material is ionic-protonic conductor at low temperature and becomes electronic one at high temperature.     

Order-disorder transition in Nd2−yGdyZr2O7 pyrochlore solid solution: An X-ray diffraction and Raman spectroscopic study

Powder X-ray diffraction (XRD) and Raman spectroscopic study of order-disorder-phase transition with increase in the content of Gd in Nd_2−yGd_yZr₂O₇ solid solution is being reported. It has been observed from Rietveld analysis that with increase in concentration of Gd in Nd_2−yGd_yZr₂O₇, the value of the x parameter of the 48f oxygen changes from 0.332(1) to 0.343(1) with a sudden change in the slope for y=1.8, which indicates that the structure is transforming from ordered pyrochlore to disordered pyrochlore. In addition to that a sudden and drastic change in the Raman spectra including changes in the position and width of several Raman modes beyond y?1.8 has also been observed which has been correlated with increasing disorder. Based on these studies, it is suggested that there is a discontinuous order-disorder transition from ‘perfect pyrochlore’ to ‘defect pyrochlore’ phase in Nd_2−yGd_yZr₂O₇ solid solution.     

Crystal structure, spectroscopy and thermodynamic properties of MVWO6(M – Li, Na)

In the present work lithium (sodium) vanadium tungsten oxides with brannerite structure is refined by the Rietveld method (space group C2/m, Z=2). IR and Raman spectroscopy was used to assign vibrational bands and determine structural particularities. The diffuse reflectance spectra allow to calculate bandgap for M^IVWO₆(M^I – Li, Na). The temperature dependences of heat capacity have been measured first in the range from 7 to 350 K for these compounds and then between 330 and 640 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity C_p^o(T), enthalpy H^o(T)−H^o(0), entropy S^o(T)−S^o(0) and Gibbs function G^o(T)−H^o(0), for the range from T→0 to 640 K. The differential scanning calorimetry was applied to measure decomposition temperature of compounds under study.     

Synthesis of Layered Sodium Manganese Phosphate via Low-heating Solid State Reaction and Its Properties

The layered nanocrystalline sodium manganese phosphate was synthesized by low‐heating solid state reaction using MnSO₄·H₂O and Na₃PO₄·12H₂O as raw materials. The resulting sodium manganese phosphate and its calcined products were characterized using element analysis, thermogravimetry and differential thermal analyses (TG/DTA), Fourier transform IR (FT‐IR), X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), ultraviolet‐visible (UV‐Vis) absorption spectroscopy, and magnetic susceptibility. The results showed that the product obtained at 70°C for 3 h, NaMnPO₄·3H₂O, was a layered compound, and its crystallite size and interlayer distance were 27 nm and 1.124 nm, respectively. The thermal process of NaMnPO₄·3H₂O between room temperature and 700°C experienced three steps, the dehydration of the one adsorption water at first, and then dehydration of the two crystal waters, at last crystallization of NaMnPO₄. Magnetic susceptibility measurements of NaMnPO₄· 3H₂O from room temperature to 2.5 K point to ferrimagnetic ordering at T_N‐35 K.     

Spectroscopic and thermal properties of FeHg(SCN)4

The preparation and characterization of iron mercury thiocyanate, FeHg(SCN)₄ (abbreviated as FMTC) are described. The spectroscopic properties were characterized by X-ray powder diffraction (XRPD), infrared, Raman and UV-Vis-NIR transmission spectra. The thermal stability and thermal decomposition of FMTC were investigated by means of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The intermediates and final products of the thermal decomposition were identified by X-ray powder diffraction at room temperature.     

三氧化二硼和五硼酸钠水合物非晶结构

X射线衍射法测量了三氧化二硼及五硼酸钠水合物的非晶结构, 通过非晶衍射实验数据处理, 得到了它们的径向分布函数(RDF). 模型定量计算, 得到了其短程有序结构, 三氧化二硼水合物非晶中75%的硼参与形成平面硼氧六元环(boroxol), 给出了环内ortho-B-O, meta-O-O, meta-B-B和para-B-O相互作用的距离和作用数, 支链与硼氧六元环之间的夹角为125°±15°; 五硼酸钠水合物非晶中, 由两个硼氧三角形(B_△)和一个硼氧四面体(B_□)构成的两个变形六元环通过公共顶点(B_□)相连而形成五硼酸阴离子, 高度有序的离子内相互作用占绝对优势. 六配位Na^＋与五硼酸阴离子中一端氧相连, Na-B特征距离为0.330 nm.     

Stability of poly(l‐lactic acid) in textile applications

The present paper is focused on the use of promising bio‐based thermoplastic—poly(l ‐lactic acid)—in textile applications and with possible limits related to its enhanced sensitivity to (bio)degradation. Linear and planar fabrics made of staple were exposed to standard washing cycles imitating the maintenance of textile materials. The effect of temperature and pH of the washing bath on the degradation rate of poly(l ‐lactic acid) was monitored by the abiotic hydrolysis test. The properties of the fabrics after carrying out the tests were evaluated from the changes of mass per areal weight, strength, and morphology of the fabrics. The changes of the structure of the polymer chains were assessed by differential scanning calorimetry, by the decrease of molar masses (determined using size exclusion chromatography) and of the viscosity of the polymer solutions, and by infrared spectroscopy. Poly(l ‐lactic acid) fabric finds application for various kinds of garments, and untreated fabric reliably tolerates 60 standard washing cycles. Copyright © 2014 John Wiley & Sons, Ltd.     

Light-induced structural changes in (HgBr2)3(As4S4)2: An X-ray single-crystal diffraction,Raman spectroscopy and ab initio study

To investigate the behaviour of the As₄S₄ molecule within a crystal-chemical environment differing from realgar, α-As₄S₄, and its high-temperature polymorph, β-As₄S₄, the effects of the light exposure on the structure of the (HgBr₂)₃(As₄S₄)₂ adduct have been studied. Differently from the cases previously studied, the action of the light filtered using a 550 nm long-wavelength pass filter did not produce any evident effect on the unit-cell. On the other hand, employing the 440 nm long-wavelength pass filter, remarkable variations of the unit-cell parameters were observed. In particular, an increase of the a, c, and β, and a decrease of the b parameter, producing on the whole an expansion of the unit-cell volume, is observed as a function of the light exposure times. Structure refinements indicated that the increase of the unit-cell volume is to ascribe to the formation of an increasing fraction (up to 20%) of pararealgar-type replacing the realgar-type molecule. Further light-exposure did not cause any further increase of the lattice parameters. On the contrary, a decrease of the unit-cell volume occurred by keeping the crystal in the dark (46 days): due to the loss of the crystallinity, only the core of the crystal, less altered and with smaller unit-cell volume, contributes to the diffraction effects. Micro-Raman spectra were collected on crystals exposed to the above mentioned wavelength light for increasing times. The peak at 275(±1) cm⁻¹ whose intensity increases as a function of the exposure time confirms the transition from a realgar- to a pararealgar-type molecule in the (HgBr₂)₃(As₄S₄)₂ adduct. Relativistic DFT-GGA ab initio band structure calculations reveal a direct band gap of 2.04 eV and quite flat valence and conduction bands around the Fermi level. According to analyses of the atomic orbital contributions to the electronic band structures the highest occupied states are attributed to non-bonding p-states of As.     

Cuprophilic Interactions in and between Molecular Entities

Despite being weak attractive forces, closed-shell metallophilic interactions play important roles in the Group 11 metal complexes on their diverse structural and physical features. A plethora of experimental and computational studies has thus been dedicated to such weak attractive d¹⁰–d¹⁰ interactions, particularly aurophilic and argentophilic interactions. Although d¹⁰–d¹⁰ Cu^I–Cu^I forces had been recognized for four decades, cuprophilic interactions are less explored and they are best evidenced by single-crystal X-ray crystallographic analysis on Cu^I complexes and aggregates thereof, by which precise information about the Cu⋅⋅⋅Cu contacts, shorter than the sum of two van der Waals radii (3.92 Å) between the copper centers concerned can be obtained. Based on recently compelling experimental and spectroscopic evidence for intra- and intermolecular cuprophilic interactions in copper chemistry, the present Minireview summarizes recent progress in the past three decades in the synthesis and structures of multinuclear homometallic copper complexes, whereby supported and unsupported d¹⁰–d¹⁰ Cu^I–Cu^I interactions are at work.     

DSC Monitoring of the Spin Crossover in Fe(II) Complexes

Heat flow to [Fe(bzimpy)²](ClO₄)₂⋅0.25H₂O complex (bzimpy=2,6-bis(benzimidazol-2-yl)pyridine) (I) was measured between 300 and 460 K by differential scanning calorimetry. This exhibits a well-developed peak characteristic of the first-order phase transitions at temperature 403 K. The enthalpy and entropy of transition from low-spin to high-spin state has been determined to be ΔH=17 kJ mol⁻¹ and ΔS=43.0 Jmol⁻¹ K⁻¹. Heat flow to [Fe(bzimpy_−1H)₂]⋅H₂O complex (bzimpy _−1H=deprotonated bzimpy) (II) was measured between 300 and 580 K. The spin crossover in this system is accompanied with liberation of crystal water on the first heating. To monitor the structural changes during the spin crossover, powder diffraction data have been collected as a function of temperature. This revised version was published online in August 2006 with corrections to the Cover Date.     

The influence of storage conditions on the polymorphic stability of zolpidem tartrate hydrate

The polymorphic stability of a drug substance is a very important topic in the pharmaceutical industry. Differential scanning calorimetry, thermogravimetric analysis with the support of X-ray powder diffraction and infrared spectroscopy were used as screening techniques for testing structural changes of zolpidem tartrate hydrate stored under different conditions. Obtained data suggested that first structural changes occurred at the temperature of 25°C after 2 months of storage. DSC analysis showed that there was a two-step process of water elimination and lack of a phase transition in the temperature range from 130 to 170°C in comparison with an initial sample.     

Pressure-induced transition in Tl2MoO4

Tl₂MoO₄ has been studied under high-pressure by X-ray diffraction, Raman spectroscopy, and optical absorption measurements. A first-order phase transition is observed at 3.5±0.5 GPa. The nature (ordered vs. disordered) of the high-pressure phase strongly depends on the local hydrostatic conditions. Optical absorption measurements tend to show that this transition is concomitant with an electronic structure transformation. Prior to the transition, single crystal X-ray diffraction shows that pressure induces interactions between MoO₄ fragments and the Mo coordination number tends to increase. In addition, the stereoactivity of the lone-pair electrons on the three symmetrically independent Tl-sites is not uniform; while for two sites the stereoactivity decreases with increasing pressures for the third site the stereoactivity increases.