Volatile zirconium complexes with sterically hindered β-diketonates: Structure and thermal properties

The structure and thermal properties of a novel zirconium(IV) complex with a methoxy substituted β-diketonate ligand tetrakis-(2-methoxy-2,6,6-trimethylheptane-3,5-dionato)zirconium are described. The complex sublimes without decomposition under low pressure (10^–2 Torr) at 200 °C. The crystal structure of the complex is molecular and is composed of two structural Zr(zis)₄ isomers in a 1:1 ratio. The crystallographic data are as follows: C₈₈H₁₅₂F₂₄O₂₄Zr₂, P-1, a = 12.1350(7) Å, b = 19.7733(10) Å, c = 21.0526(12) Å, α = 83.338(2)°, β = 89.571(2)°, γ = 73.515(2)°, V = 4809.5(5) ų, Z = 2, d = 1.227 g/cm³. The coordination environment of the zirconium atom consists of eight oxygen atoms from four β-diketonate ligands; the coordination polyhedron is a square antiprism. The Zr–O distances are in a range 2.127-2.202 Å. The thermal properties of the complex are studied by TG–DTA. The effect of the crystal structure (molecular packing) on the volatility and thermal properties is compared for the new complex and two other analogous zirconium complexes with β-diketonate ligands containing bulky terminal substituents. The results of the mass spectrometric study of thermal behavior of the complexes on programmed heating of vapor under the conditions similar to those in a hot wall CVD reactor under low pressure, including the decomposition in the presence of oxygen, are discussed.     

New Phosphate-Sulfates with NZP Structure

NaZr_2–xB_x(PO₄)_3–2x(SO₄)_2x (0 ≤ x ≤ 1.25, B = Mg, Co, Ni, Cu, Zn), and NaZr_2–xR_x(PO₄)_3–x(SO₄)_x (0 ≤ x ≤ 1.25, R = Al, Fe) phosphate-sulfates series have been prepared by a sol–gel process. These compounds belong to the NaZr₂(PO₄)₃ (NZP) structure family and crystallize in hexagonal crystal system, space group R\(\bar 3\)c. Limited solid solution series were found to exist; their formation temperatures and thermal stability limits were determined. Particle sizes as determined by microstructure observation were 50–200 nm, and for Cu- and Zn-containing samples, 200–500 nm. The thermal expansion of phosphate-sulfate NaZr_1.25Cu_0.75(PO₄)_1.5(SO₄)_1.5 was studied in the range 25–700°C. Thermal expansion coefficients and thermal expansion anisotropy were found to be α_a =–5.40 × 10^–6 °C^–1, α_с = 18.88 × 10^–6 °C^–1, α_avg = 2.69 × 10^–6 °C^–1, and Δα = 24.28 × 10^–6 °C^–1.     

Thermal stability of chlorophyll <Emphasis Type="Italic">a</Emphasis> derivatives containing hydrophilic groups

Trends in thermal stability of aromatic macroheterocycles based of pheophorbide a and chlorin e ₆ containing hydrophilic groups have been revealed by means of thermogravimetric analysis at 298–1223 K under inert atmosphere. Methylpheophorbide a and 13(1)-N-methylamide of chlorin e ₆ are the most stable, the decomposition onset temperature being t _o 351 and 333°С. Their functional substitution leads t _o the reduction in thermal stability. Depending on the macrocycle structure the decrease in t _o can reach 20–200°С.     

Preparation and thermal reliability of <Emphasis Type="Italic">N</Emphasis>-butyl stearate/methyl palmitate composite phase change material

In this study, a series of binary mixtures of N-butyl stearate (nBS) and methyl palmitate (MP) were used to produce a novel composite phase change material (CPCM) for potential application in the eastern China, and their thermal properties were investigated by differential scanning calorimetry (DSC). The results of DSC indicated that the mixture consisting of 10 mass% nBS and 90 mass% MP is optimum as the CPCM in terms of the phase change temperature ranges (T _f = 19.74–5.59 °C; T _m = 18.34–33.80 °C) and latent heats (ΔH _f = 176.8 J g^?1; ΔH _m = 189.3 J g^?1). On the other hand, the thermal reliability and chemical stability of the CPCM after 120, 180, 240, 300, 360 and 500 accelerated thermal cycling tests were studied by DSC and fourier transform infrared (FTIR) analysis. The results demonstrated that the CPCM had good thermal reliability and chemical stability.     

Temperature-dependent AC electrical conductivity,thermal stability and different DC conductivity modelling of novel poly(vinyl cinnamate)/zinc oxide nanocomposites

Thermal analysis on organically modified Ca²⁺-montmorillonite (OMON) and its source materials—octadecylamine (ODA) and Ca²⁺-montmorillonite (Ca²⁺-Mon)—was studied using thermally stimulated current (TSC) technique. The appearance of ρ _MON peak with the T _max = 75 °C shows the ability of the developed TSC system to demonstrate the relaxation effects of dehydration in Ca²⁺-Mon. It appeared within the temperature range of DSC endothermic peak (30–100 °C) where the T _mMON = 58 °C. Segmental motions of ODA chains and structural disruptions in the modifier agent compound produced TSC α _ODA, ρ _ODA and ρ _1ODA peaks that are comparable to thermal transition and endothermic peaks in DSC profile (T _gODA, T _m1ODA and T _m2ODA). The effect of localized motion in ODA chains as revealed by the TSC β_OMON peak (T _max = ?23 °C), however, is absent in the DSC profile of OMON. It shows TSC technique has high sensitivity in detecting various relaxation behaviors at molecular level. More evidences are demonstrated by the ρ _OMON (T _max = 86 °C) and ρ _1OMON (T _max = 105 °C) peak originated from the ODA chains structures. These peaks also confirm the intercalation of the modifier cations inside the Ca²⁺-Mon gallery.     

Kinetics of thermal decomposition of sulfur-containing amino acids

Rates of thermal decomposition of sulfur-containing amino acids such as D,L-methionine, L-cysteine, and L-cystine are studied. It is established that the amino acids decompose at 190–240°C to give the gaseous and liquid decomposition products in the polyphasic system formed. The rate of summary process is described by the first order kinetic equation up to 30–50% conversion. In spite of close values of the effective activation energies of thermal decomposition of D,L-methionine, L-cysteine, and L-cystine (195, 193, and 184 kJ mol^?1 respectively) the effective rate constants at one and the the same temperature differ by one or two orders of magnitude in the above-mentioned series. Sulfur-containing compounds prevail in the gaseous decomposition products, while in the liquid phase the nitrogen-containing ones are accumulated.     

Synthesis and study of high-temperature heat capacity of erbium orthovanadate

Orthovanadate ErVO₄ has been prepared by solid-phase synthesis from a stoichiometric mixture of high pure V₂O₅ and chemically pure Er₂O₃ by multistage calcination in air in the temperature range 873–1273 K. The effect of temperature (380–1000 K) on the heat capacity of orthovanadate ErVO₄ was studied by hightemperature calorimetry. Thermodynamic properties of erbium orthovanadate (enthalpy change H°(T)–H°(380 K), entropy change S°(T)–S°(380 K), and reduced Gibbs energy Φ°(T)) have been calculated from the experimental C_p = f(T) data. It has been shown that the specific heat varies in a row of oxides and orthovanadates of Gd-Lu naturally depending on the radius of the R³⁺ ion within the third and fourth tetrads.     

Heat capacities and thermodynamic functions of new nanosized ferro-chromo-manganites LaM<Subscript>0.5</Subscript><Superscript>II</Superscript>FeCrMnO<Subscript>6.5</Subscript> (M<Superscript>II</Superscript>–Mg,Ca, Sr,Ba)

The heat capacities of nanosized ferro-chromo-manganites LaM_0.5 ^IIFeCrMnO_6.5 (M^II–Mg, Ca, Sr, Ba) are measured via dynamic calorimetry in the temperature range of 298.15–673 K using an IT-S-400 instrument. It is established that the C°_p~f(T) function of LaM_0.5 ^IIFeCrMnO_6.5 (M^II–Mg, Ca, Sr, Ba) has λ-type effects, due probably to phase transitions of the second order. Considering the temperatures of the phase transitions, equations of the heat capacity of ferro-chromo-manganites LaM_0.5 ^IIFeCrMnO_6.5 (M^II–Mg, Ca, Sr, Ba) as a function of temperature are derived on the basis of experimental data. Thermodynamic functions Н°(Т)–Н°(298.15), S°(Т), and Ф ^хх(Т) are calculated in the temperature range of 298.15–675 K.     

Synthesis of Block Copolymers of Styrene with <Emphasis Type="Italic">D</Emphasis>,<Emphasis Type="Italic">L</Emphasis>-Lactide by the Sequential Controlled Cationic Polymerization and Ring-Opening Anionic Polymerization

The cationic polymerization of styrene initiated by the system 2-chloro-2-phenylpropane–TiCl₄–pyridine is studied in a mixture CH₂Cl₂–n-hexane at a temperature of –80°С. It is shown that under these conditions polymerization occurs via the living mechanism at [monomer]: [initiator] ≤ 100. The method of preparing polystyrenes with terminal primary hydroxyl groups (M_n = 4000–10000 g/mol) by the sequential controlled cationic polymerization of styrene and the in situ alkylation of 4-phenoxy-1-butanol by polystyrene macrocations is proposed. The resulting functionalized polystyrenes are used as macroinitiators of anionic-coordination ring-opening polymerization of D,L-lactide in the presence of tin bis(2-ethyl hexanoate) [Sn(Oct)₂] in toluene at 80°С. Copolymers polystyrene-block-poly(D,L-lactide) with the controlled length of the poly(D,L-lactide) block (M_n = 10000–17000 g/mol) and a relatively low molecular-weight distribution (M_w/M_n = 1.6–1.8) are synthesized. Formation of the block copolymers is confirmed by ¹Н NMR spectroscopy, gel-permeation chromatography, and atomic force microscopy.     

Evaporation of Plasticizer from NEPE Type Propellant

Using the method of dynamic thermogravimetry and differential scanning calorimetry in the heating rate range 0.46–10.0 deg^–1 min^–1, evaporation of the plasticizer from propellant samples of the NEPE type was investigated. The experiments were carried out in an open system in a flow of pure argon at atmospheric pressure. Nitroglycerin is the main mass fraction of the plasticizer. The activation energy E of the gross evaporation–diffusion process is determined by various methods. Heat of evaporation of the plasticizer ΔH_v is estimated. It is shown that in the early stage of evaporation the values of E and ΔH_v practically coincide. At a temperature of 298.15 K ΔH_v = 89 ± 4 kJ mol^–1, which is in satisfactory agreement with the literature data for heat of evaporation of pure nitroglycerin. With any way of preventing free removal of the plasticizer from the surface of the samples on the DSC thermograms successive exothermic peaks of the thermal decomposition of the plasticizer and the octogen are observed, which are not realized in the open system for the indicated heating rates at T < 190°C.     

Synthesis and characterization of crystallizable aliphatic thermoplastic poly(ester urethane) elastomers through a non-isocyanate route

A simple non-isocyanate route is developed for synthesizing crystallizable aliphatic thermoplastic poly(ester urethane) elastomers(TPEURs) with good thermal and mechanical properties. Three prepolymers of1,6-bis(hydroxyethyloxycarbonylamino) hexane(BHCH), i.e. Pre PBHCHs, were prepared through the self-transurethane polycondensation of BHCH. A poly(butylene adipate) prepolymer(Pre PBA) with terminal HO― groups was prepared and used as a polyester glycol. A series of TPEURs were prepared by the co-polycondensation of the Pre PBHCHs with Pre PBA at 170 ℃ under a reduced pressure of 399 Pa. The TPEURs were characterized by gel permeation chromatography, FTIR,1H-NMR, differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray diffraction, atomic force microscopy, and tensile test. The TPEURs exhibited M_n up to 23300 g/mol, M_w up to 51100 g/mol, Tg ranging from-33.8 ℃ to-3.1 ℃, T_m from 94.3 ℃ to 111.9 ℃, initial decomposition temperature over 274.7 ℃, tensile strength up to18.8 MPa with a strain at break of 450.0%, and resilience up to 77.5%. TPU elastomers with good crystallization and mechanical properties were obtained through a non-isocyanate route.     

Molecular Layer Deposition and Thermal Transformations of Titanium(Aluminum)-Vanadium Hybrid Organic-Inorganic Films

In this work Molecular layer deposition (MLD) technique used to synthesize titanium-vanadium (TiV _x C _y O _z ) and aluminum-vanadium (AlV _x C _y O _z ) hybrid organic-inorganic films via alternating surface reactions of titanium tetrachloride (or trimethylaluminum), vanadium oxochloride, and ethylene glycol. Using in situ monitoring it was found that the surface reactions were self-limiting at temperatures of 90 and 115°C. The coating thickness per molecular layer deposition cycle (growth rate) at 115°C on a silicon substrate varied from 5.8 to 11.4 Å/cycle, and the film densities, from 1.7 to 2.0 g cm^–3. An analysis of the samples obtained at 115°C revealed their amorphous structure. A thermal treatment of titanium-vanadium films at 450°C in air resulted in formation of highly structured coatings. These coatings were composed of nanowires of single-crystal vanadium oxide (V₂O₅) and mixed nanostructures of titanium and vanadium oxides. Increase in thermal treatment temperature to 500°C resulted in elongation of the V₂O₅ nanowires up to tens of micrometers and in their separation from the substrate. A thermal treatment of aluminum-vanadium films in air resulted in formation of a low-density film. Pyrolysis of the films in an inert gas yielded composite coatings containing domains of graphitized carbon. These films can be potentially useful in modern devices for energy storage, electronics, medicine and other promising fields of technology.     

Thermal deformation thermodynamics of a smectite mineral

A method has been purposed to calculate some of the thermodynamic quantities for the thermal deformation of a smectite without using any basic thermodynamic data. The Hanç?l? (Keskin, Ankara, Turkey) bentonite containing a smectite of 88% by volume was taken as material. Thermogravimetric (TG) and differential thermal analysis (DTA) curves of the sample were obtained. Bentonite samples were heated at various temperatures between 25–900°C for the sufficient time (2 h) until to establish the thermal deformation equilibrium.Cation-exchange capacity (CEC) of heated samples was determined by using the methylene blue standard method. The CEC was used as a variable of the equilibrium. An arbitrary equilibrium constant (K _a) was defined similar to chemical equilibrium constant and calculated for each temperature by using the corresponding CEC-value. The arbitrary changes in Gibbs energy (ΔG _a ⁰ ) were calculated from K _a-values. The real change in enthalpy (ΔH ⁰) and entropy (ΔS ⁰) was calculated from the slopes of the lnK vs. 1/T and ΔG vs. T plots, respectively. The real changes in Gibbs energy (ΔG ⁰) and real equilibrium constant (K) were calculated by using the ΔH ⁰ and ΔS ⁰ values. The results at the two different temperature intervals are summarized as below: ΔG ₁ ⁰ =ΔH ₁ ⁰ ?ΔS ₁ ⁰ T=?RTlnK ₁=47000?53t, (200–450°C), and ΔG ₂ ⁰ =ΔH ₂ ⁰ -ΔS ₂ ⁰ T=?RTlnK ₂=132000?164T, (500–800°C).     

Polymeric lithium(I) diaquabarbiturate: Crystal structure

The lithium(I) catena-diaquabarbiturate complex [Li(H₂O)₂(HBA–O,O′)] _n (I), where Н₂ВА is barbituric acid, has been structurally characterized by X-ray diffraction (CIF file CCDC no. 1447689), and its thermal decomposition and IR spectrum have been studied. Crystals of complex I are monoclinic, a = 6.4306(7) Å, b = 16.720(1) Å, c = 7.1732(8) Å, β = 108.253(4)°, V = 732.5(1) ų, space group P2₁/c, and Z = 4. One independent μ₂-bridging HBA^– ligand is coordinated to two Li(I) ions via the two oxygen atoms of C₄₍₆₎=O carbonyl groups. Each Li⁺ ion is linked with two μ₂-HBA^– ions and two terminal water molecules at tetrahedron vertices. μ₂-HBA^– ions link tetrahedra into a chain. The structure is stabilized by multiple hydrogen bonds and π–π-interaction between HBA^–. The shift of ν(C=O) vibration bands in the IR spectrum of complex I in comparison with Н₂ВА towards lower frequencies agrees with the coordination of HBA^– via oxygen atoms. The dehydration of complex I occurs in two stages in the regions of 100–150 and 150–240°C.     

Thermal properties of dimethylgold(III) 8-hydroxyquinolinate and 8-mercaptoquinolinate

Dimethylgold(III) complexes with 8-hydroxyquinoline Me₂Au(Ox) (I) and 8-mercaptoquinoline Me₂Au(Tox) (II) were synthesized and studied. Complex II obtained for the first time was identified from the elemental analysis, IR, ¹H NMR, and mass spectrometry data. The thermal properties of complexes I, II in condensed state were investigated by thermography. The temperature dependences of the saturated vapor pressure over crystals were measured by the Knudsen effusion method with mass spectrometric recording of the gas phase composition and the thermodynamic characteristics of the sublimation process were determined: for I, log P[Torr] = (14.6 ± 0.3) ? (6.34 ± 0.10) × 10³/(T, K), Δ H _subl ^o = 121.2 ± 1.9 kJ^?1, Δ S _subl ^o = 224.1 ± 4.6 J mol^?1 K^?1 (the temperature interval under study 80–115°C); for II, log P [Torr] = (13.3 ± 0.2) ? (6.30 ± 0.09) × 10³/(T, K), Δ H _subl ^o = 120.5 ± 1.7 kJmol^?1, ΔS _subl ^o = 199.3 ± 3.0 J mol^?1 K^?1 (86–145°C).     

Standard Thermodynamic Functions of Crystalline Arsenate Mg<Subscript>0.5</Subscript>Zr<Subscript>2</Subscript>(AsO<Subscript>4</Subscript>)<Subscript>3</Subscript> in the Range from <Emphasis Type="Italic">T</Emphasis> → 0 to 670 K

The temperature dependence of heat capacity C^° _p = f(T) of crystalline arsenate Mg_0.5Zr₂(AsO₄)₃ was studied by precision adiabatic vacuum and differential scanning calorimetry in the temperature range 8?670 K. The standard thermodynamic functions C^° _p (T), H°(T)–H°(0), S°(T), and G°(T)–H°(0) of the arsenate for the range from Т → 0 to 670 K and the standard formation entropy at Т = 298.15 K were calculated from the obtained experimental data. Based on the low-temperature capacity data (30–50 K) the fractal dimension D of the arsenate was determined, and the topology of its structure was characterized. The results were compared with the thermodynamic data for the structurally related crystalline phosphates M_0.5Zr₂(PO₄)₃ (M = Mg, Ca, Sr, Ba, Ni) and arsenate NaZr₂(AsO₄)₃.     

Molecular structure and conformation of nitrobenzene reinvestigated by combined analysis of gas-phase electron diffraction,rotational constants,and theoretical calculations

The molecular structure and conformation of nitrobenzene has been reinvestigated by gas-phase electron diffraction (GED), combined analysis of GED and microwave (MW) spectroscopic data, and quantum chemical calculations. The equilibrium r _e structure of nitrobenzene was determined by a joint analysis of the GED data and rotational constants taken from the literature. The necessary anharmonic vibrational corrections to the internuclear distances (r _e ? r _a) and to rotational constants (B _e ⁽ⁱ⁾  ? B ₀ ⁽ⁱ⁾ ) were calculated from the B3LYP/cc-pVTZ quadratic and cubic force fields. A combined analysis of GED and MW data led to following structural parameters (r _e) of planar nitrobenzene (the total estimated uncertainties are in parentheses): r(C–C)_av = 1.391(3) Å, r(C–N) = 1.468(4) Å, r(N–O) = 1.223(2) Å, r(C–H)_av = 1.071(3) Å, \({\angle}\)C2–C1–C6 = 123.5(6)°, \({\angle}\)C1–C2–C3 = 117.8(3)°, \({\angle}\)C2–C3–C4 = 120.3(3)°, \({\angle}\)C3–C4–C5 = 120.5(6)°, \({\angle}\)C–C–N = 118.2(3)°, \({\angle}\)C–N–O = 117.9(2)°, \({\angle}\)O–N–O = 124.2(4)°, \({\angle}\)(C–C–H)_av = 120.6(20)°. These structural parameters reproduce the experimental B ₀ ⁽ⁱ⁾ values within 0.05 MHz. The experimental results are in good agreement with the theoretical calculations. The barrier height to internal rotation of nitro group, 4.1±1.0 kcal/mol, was estimated from the GED analysis using a dynamic model. The equilibrium structure was also calculated using the experimental rotational constants for nitrobenzene isotopomers and theoretical rotation–vibration interaction constants.     

Molecular structure,quantum chemical investigation,and thermal behavior of (DNAZ-CO)<Subscript>2</Subscript>

Bis-(3,3-dinitroazetidinyl)-oxamide ((DNAZ-CO)₂) is an acyl derivative of 3,3-dinitroazetidine (DNAZ). It is prepared and its crystal structure is determined. The crystal is orthorhombic, Fdd2 space group, a = 13.136(14) Å, b = 19.48(3) Å, c = 10.326(14) Å, V = 2642 (6) ų, Z = 8. A density functional theory (DFT) method of the Amsterdam Density Functional (ADF) package is used to calculate the geometry, frequencies, and properties. The optimized geometry, frontier orbital energy, and main atomic orbital percentage are obtained. The thermal behavior is studied under a non-isothermal condition by DSC and TG/DTG methods. The apparent activation energy (E _a) and pre-exponential factor (A) of the exothermic decomposition reaction of (DNAZ-CO)₂ are 164.10 kJmol^?1 and 10^13.38 s^?1 respectively. The critical temperature of thermal explosion is 272.20°C. The values of ΔS ^≠, ΔH ^≠, and ΔG ^≠ of this reaction are 6.44 Jmol^?1·K^?1, 163.76 kJmol^?1 and 160.34 kJmol^?1 respectively.     

Metathesis polymer based on 5-trimethylsilylbicyclo[2.2.2]oct-2-ene: Synthesis and gas-transport properties

A new silicon-containing bicyclic monomer 5-trimethylsilylbicyclo[2.2.2]oct-2-ene has been synthesized, and its metathesis polymerization and gas transport properties of the polymer based on it have been studied. The monomer is synthesized by the two-step scheme using the Diels–Alder reaction from 1,3-cyclohexadiene and vinyltrichlorosilane followed by methylation with a Grignard reagent. The resulting 5-trimethylsilylbicyclo[ 2.2.2]oct-2-ene is inactive in metathesis homopolymerization in the presence of first- and second- generation Grubbs catalysts and a Hoveyda–Grubbs catalyst, but it slowly polymerizes when norbornene is present in the reaction mixture. The high-molecular-mass copolymer (M _w = 3.0 × 10⁵, M _w/M _n = 2.8) of 5-trimethylsilylbicyclo[2.2.2]oct-2-ene and norbornene possesses good film-forming properties, and its glass transition temperature is 126°C. The gas-transport properties of the copolymer have been studied.     

Crystal structure and some properties of europium(III) <Emphasis Type="Italic">Catena</Emphasis>-{tris(1,3-diethyl-2-thiobarbiturate)}

The [Eu(HDTBA)₃]_n complex (I), HDTBA is 1,3-diethyl-2-thiobarbituric acid (C₈H₁₂N₂O₂S) is synthesized and its structure is determined by X-ray crystallography. The crystals of I are triclinic: a = 11.0205(2) Å, b = 11.8811(3) Å, c = 12.7312(2) Å, α = 100.933(1)°, β = 109.704(1)°, γ = 101.161(1)°, V = 1479.88(5) ų, space group P-1, Z = 2. Each of three independent DETBA^– ions is a bridging μ2-O,O′-coordinated ligand. The coordination polyhedron of Eu(III) is a distorted octahedron. Bridging DETBA^– organize the octahedra into an infinite two-dimensional layer. The structure contains intramolecular hydrogen bonds but intermolecular hydrogen bonds and the π–π interaction are absent. The results of IR spectroscopy and photoluminescence agree with the single crystal X-ray diffraction data. The main product of the thermal decomposition of I at 900°С is oxysulfate Eu₂O₂SO₄.