Titanium tetrafluoride complexation with phosphorylated ketone Ph<Subscript>2</Subscript>P(O)(CH<Subscript>2</Subscript>)<Subscript>2</Subscript>C(O)Me in CH<Subscript>2</Subscript>Cl<Subscript>2</Subscript>

The products resulting from the reaction of TiF₄ with Ph₂P(O)(CH₂)₂C(O)Me (L') in CH₂Cl₂ have been studied by ¹⁹F{¹H} and 31P{¹H} NMR spectroscopy. At a twofold excess of L', solution contains cis-TiF₄(L')2 (>90%), trans-TiF₄(L')₂, and fac-[TiF₃L₃']⁺, where L' is coordinated via the P=O group, as well as the dimer [(Ti₂F₇L'₂)₂]+, where L' is coordinated through the P=O and C=O groups. An equimolar solution contains dimeric and polynuclear complexes containing moieties with three terminal cis fluorine ions, while the other coordination sites are occupied by the P=O groups and F^– bridges. At a twofold excess of TiF₄, ligand L' coordinates via the P=O and C=O groups and behaves as a bridge along with F^– ions. Thermodynamic stability of the structures of the TiF₄L'₂ isomers and the structure of [(µ-F)(µ-L')₂(TiF₃)₂]⁺ has been calculated.     

Molecular structure of octachlorotrisilane Si<Subscript>3</Subscript>Cl<Subscript>8</Subscript>

The parameters of the geometrical configuration of octachlorotrisilane Si₃Cl₈ were determined by quantum-chemical and gas-phase electron diffraction methods at 303±2 K. The calculated barrier to the internal rotation of SiCl₃ groups relative to the Si-Si bond was calculated.     

Structure of aqueous dispersions of Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> nanotubes

Behavior of hydrosilicate nanotubes of composition Mg₃Si₂O₅(OH)₄ in aqueous dispersions was studied. Experiments devoted to observation of steady-state and relaxation electro-optical effects demonstrated that, irrespective of their initial concentration in water, nanotubes form stable bulk aggregates with weak anisotropy, rather than a homogeneous system of separate suspended nanosize cylinders.     

Crystal Structure of Tl<Subscript>2</Subscript>[NbCl<Subscript>6</Subscript>] and Tl<Subscript>2</Subscript>[NbBr<Subscript>6</Subscript>]

Single crystals of Tl₂[NbCl₆] (1) and Tl₂ [NbBr₆] (2) are obtained as black needles on heating TlCl, Nb, S₂Cl₂ (1) and Tl, Nb, and Br₂ at 400°C (2). Tl₂NbBr₆ also forms in the reaction of TlBr, Nb, Br₂, and S at 500°C. Both compounds crystallize in the K₂[PtCl₆] structure type to form non-distorted octahedral [NbХ₆]^2– anions (Nb–Cl 2.397(4) Å and Nb–Br 2.516(2) Å). The magnetic properties of Tl₂[NbBr₆] in a range 5-300 K indicate an antiferromagnetic interaction between Nb⁴⁺ ion spins (d¹, S = 1/2). On cooling, the compound becomes a noncollinear ferromagnet with T_c = 23 K.     

Heat capacities and absolute entropies of UTi<Subscript>2</Subscript>O<Subscript>6</Subscript> and CeTi<Subscript>2</Subscript>O<Subscript>6</Subscript>

Summary As part of a larger study of the physical properties of potential ceramic hosts for nuclear wastes, we report the molar heat capacity of brannerite (UTi₂O₆) and its cerium analog (CeTi₂O₆) from 10 to 400 K using an adiabatic calorimeter. At 298.15 K the standard molar heat capacities are (179.46±0.18) J K^-1 mol^-1 for UTi₂O₆ and (172.78±0.17) J K^-1 mol^-1 for CeTi₂O₆. Entropies were calculated from smooth fits of the experimental data and were found to be (175.56±0.35) J K^-1 mol^-1 and (171.63±0.34) J K^-1 mol^-1 for UTi₂O₆ and CeTi₂O₆, respectively. Using these entropies and enthalpy of formation data reported in the literature, Gibb’s free energies of formation from the elements and constituent oxides were calculated. Standard free energies of formation from the elements are (-2814.7±5.6) kJ mol^-1 for UTi₂O₆ and (-2786.3±5.6) kJ mol^-1 for CeTi₂O₆. The free energy of formation from the oxides at T=298.15 K are (-5.31±0.01) kJ mol^-1 and (15.88±0.03) kJ mol^-1 for UTi₂O₆ and CeTi₂O₆, respectively.     

Enthalpy of formation of talc Mg<Subscript>3</Subscript>[Si<Subscript>4</Subscript>O<Subscript>10</Subscript>](OH)<Subscript>2</Subscript> according to dissolution calorimetry

A thermochemical study of natural talc was performed by high-temperature melt dissolution calorimetry on a Tian-Calvet calorimeter. Based on the total values of the increment in enthalpy upon heating the sample from room temperature to 973 K, and of the dissolution enthalpy at 973 K measured in this work for talc and gibbsite (along with those determined for tremolite, brucite, and their corresponding oxides), the enthalpy of formation was calculated for talc composed of elements, Mg₃[Si₄O₁₀](OH)₂, at 298.15 K: Δ_f H _el^o(298.15 K) = −5900.6 ± 4.7 kJ/mol.     

Characteristics of CuAl<Subscript>2</Subscript>-Cu<Subscript>9</Subscript>Al<Subscript>4</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites synthesized by mechanical treatment

Summary Reactive milling of Cu-hydroxycarbonate - powder aluminium mixture brings many complex chemical reactions such as decomposition, aluminothermic reduction and mechanical alloying resulting in the formation of nanometer size composites that contain intermetallic phases, -Cu₉Al₄ and -CuAl₂, with aluminium oxide.     

Crystallization kinetics and thermal stability of an amorphous Fe<Subscript>77</Subscript>C<Subscript>5</Subscript>B<Subscript>4</Subscript>Al<Subscript>2</Subscript>GaP<Subscript>9</Subscript>Si<Subscript>2</Subscript> bulk metallic glass

The thermal stability, kinetics and glass forming ability of an Fe₇₇C₅B₄Al₂GaP₉Si₂ bulk amorphous alloy have been studied by differential scanning calorimetry. The activation energy, frequency factor and rate constant corresponding to the multiple crystallization steps were determined by the Kissinger method. X-ray diffraction and transmission electron microscopy studies revealed that the crystallization starts with the primary precipitation of α-Fe from the amorphous matrix. The kinetics of nucleation of the α-Fe nanoparticles was investigated by two different methods, i.e. isothermal annealing and continuous heating after partial annealing.     

Sb<Subscript>2</Subscript>S<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> nanocomposite layers synthesized using the layer-by-layer technique

Possibility of layer-by-layer synthesis by colloidal layering of Sb₂S₃-SiO₂ nanocomposite layers from colloid solutions of {[H _x Sb₂S₅] ^m ?}mNa⁺ and SiO₂ was studied. The composition of the layers synthesized was examined by Raman spectroscopy, transmission spectroscopy in the UV and visible spectral ranges, energy-dispersion micro analysis, and scanning electron microscopy.     

Relative Raman Intensities in C<Subscript>6</Subscript>H<Subscript>6</Subscript>, C<Subscript>6</Subscript>D<Subscript>6</Subscript>, and C<Subscript>6</Subscript>F<Subscript>6</Subscript>: A Comparison of Different Computational Methods

The accuracy of various computational methods (Hartree–Fock, MP2, CCSD, CAS-SCF, and several types of DFT) for predicting relative intensities in Raman spectra for C₆H₆, C₆D₆, and C₆F₆ was compared. The predicted relative intensities for ν₁ and ν₂ were compared with relative intensities measured by an FT-Raman spectrometer. While none of these methods excelled at this prediction, Hartree–Fock with a large basis set was most successful for C₆H₆ and C₆D₆, while PW91PW91 was the most successful for C₆F₆.     

Isomorphism in the KTaWO<Subscript>6</Subscript>-RbTaWO<Subscript>6</Subscript>-CsTaWO<Subscript>6</Subscript> system

Synthetic procedures have been developed and compounds of composition K _x Rb _y Cs _z TaWO₆ (x + y + z = 1) have been obtained. Their structure has been investigated by X-ray diffractometry. It has been shown that a continuous series of solid solutions is formed in the ternary system under study. Thermal decomposition of A^ITaWO₆ compounds (A^I = K, Rb, Cs) has been investigated by high-temperature X-ray diffractometry.     

The synthesis and thermochemical study of (Mg,Fe)<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> nanotubes

Nanotubular (Mg,Fe²⁺,Fe³⁺)₃Si₂O₅(OH)₄ hydrosilicates with a chrysotile structure were synthesized under hydrothermal conditions. The phases prepared were studied thermochemically on a high-temperature Tian-Calvet microcalorimeter by solution calorimetry. The standard enthalpies of formation of magnesium-iron nanotubular hydrosilicates were determined. The formation of iron-containing nanotubes was shown to be lass favorable energetically than the formation of magnesium nanotubes.     

Effect of heat treatment on structural-chemical transformations in magnesium hydrosilicate [Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript>] nanotubes

The structural-chemical transformations in nanotubular magnesium hydrosilicate of composition Mg₃Si₂O₅(OH)₄ (chrysotile) obtained by hydrothermal synthesis were studied in heating to 1200°C.     

Synthesis and characterization of a new monophosphate (C<Subscript>6</Subscript>H<Subscript>16</Subscript>N<Subscript>2</Subscript>)(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Chemical preparation, crystal structure, and NMR spectroscopy of a new trans-2,5-dimethylpiperazinium monophosphate are given. This new compound crystallizes in the triclinic system, with the space group P-1 and the following parameters: a = 6.5033(3), b = 7.6942(4), c = 8.1473(5) Å, α = 114.997(3), β = 92.341(3), γ = 113.136(3), V = 329.14(3) ų, Z = 1, and D_x = 1.565 g cm^?3. The crystal structure has been determined and refined to R = 0.030 and R _w(F ²) = 0.032 using 1558 independent reflections. The structure can be described as infinite [H₂PO₄] _n ^n? chains with (C₆H₁₆N₂)²⁺ organic cations anchored between adjacent polyanions to form columns of anions and cations running along the b axis. This compound has also been investigated by IR, thermal, and solid-state, ¹³C and ³¹P MAS NMR spectroscopies and Ab initio calculations.     

Preparation and characterization of luminescent cellulose–Y<Subscript>4</Subscript>Si<Subscript>2</Subscript>O<Subscript>7</Subscript>N<Subscript>2</Subscript>:Ce<Superscript>4+</Superscript> hybrid hydrogels

Novel luminescent bio-based hydrogels comprising cellulose and Y₄Si₂O₇N₂:Ce⁴⁺ (YC) were prepared in an alkali/urea aqueous system using epichlorohydrin as a cross-linker. The structure, characteristics and properties of the hydrogels were investigated by various techniques, including FTIR spectroscopy, wideangle X-ray diffraction, scanning electron microscopy, etc. The results showed that when the content of YC was less than 0.05 g, the YC particles were tightly embedded in the macro porous of cellulose matrix, which not only supplied cavities for YC immobilization, but also supplied the pore wall to protect the structure and character of YC. Hence, the cellulose–YC hybrid hydrogels exhibited strong cyan fluorescence under a UV lamp. However, excess of YC particles were enshrouded in the cellulose matrix resulted in smaller pores, weaker fluorescence intensity, lower swelling ratio and higher mechanical properties.     

Thermal analysis on C<Subscript>6</Subscript>H<Subscript>10</Subscript>Ge<Subscript>2</Subscript>O<Subscript>7</Subscript>-doped MgB<Subscript>2</Subscript>

Additives to MgB₂ can improve the superconducting functional characteristics, such as critical current density (J _c) and irreversibility field (H _irr). Recently, we have shown that repagermanium (C₆H₁₀Ge₂O₇) is an effective additive, enhancing both J _c and H _irr. To look into details of the processes taking place during the reactive sintering, a thermal analysis study (0.167 K s^?1, in Ar) is reported. We used differential scanning calorimetry between 298 and 863 K and simultaneous thermogravimetric—differential thermal analysis between 298 and 1233 K. Samples were mixtures of powders with composition 97 mol% MgB₂ and 3 mol% C₆H₁₀Ge₂O₇. Up to 863 K, repagermanium decomposes by multiple steps and forms amorphous phases. A reaction with MgB₂ is not observed. Above this temperature, partial decomposition of MgB₂ occurs. Crystalline Ge and MgO are detected before formation of Mg₂Ge and MgB₄, when temperature approaches the melting point of Ge (1211 K). Carbon substitution for boron in the crystal lattice of MgB₂ is observed for samples heated above 863 K. The amount of substitutional C does not significantly change with temperature.     

Thermochemical properties of MnNb<Subscript>2</Subscript>O<Subscript>6</Subscript>

Homogeneous manganocolumbite (MnNb₂O₆) was synthesized from Nb₂O₅ and MnO oxides. Powder sample was orthorhombic with unit cell parameters: α = 0.5766 nm, b = 1.4439 nm, c = 0.5085 nm and V = 0.4234 nm³. Heat capacity over the temperature range of 313–1253 K was measured in an inert atmosphere with combined thermogravimetry and calorimetry using NETZSCH STA 449C Jupiter thermoanalyzer. Melting point was 1767 ± 3 K, enthalpy of melting was 144 ± 4 kJ mol⁻¹. Experimental heat capacity of MnNb₂O₆ is fitted to polynomial C _pm = 221.46 + 3.03 · 10⁻³ T + −39.79 · 10⁵ T ⁻² + 40.59 · 10⁻⁶ T ².     

Preparation and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> submicron-belts synthesized by a sol–gel H<Subscript>2</Subscript>O<Subscript>2</Subscript> route

One-dimensional (1D) submicron-belts of V₂O₅ have been prepared by a sol–gel route using V₂O_5, H₂O₂ and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement and cyclic voltammeter. The results showed that the synthesized V₂O₅ appeared to be submicron-belts and orthorhombic structure. The V₂O₅ submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge rate in the potential region 1.8–4.0 V.     

The Role of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgO Additives on the Photoluminescence Properties of Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Nanoparticles

The current research addressed synthesizing and studying photoluminescence studies of β-Si₃N₄ nanoparticles. The effect of MgO and Y₂O₃ as the typical additives on photoluminescence behaviour was evaluated. The β-Si₃N₄ with MgO and Y₂O₃ additive specimens were fabricated by a solid state technique (ball-milled method). The as-prepared products were characterized by X-ray diffraction technique, transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman analysis. The results showed that after ball-milled process, hexagonal β-Si₃N₄ with MgO or Y₂O₃ as the additives with the size distribution of 45–50 nm was obtained. The optical properties of the as-synthesized product were also investigated by photoluminescence and diffuse reflection spectroscopy. The obtained results confirmed that employing MgO as an additive, in comparison to the Y₂O₃, could enhance emission properties in the synthesized silicon nitride nanoparticles. The obtained results also showed that MgO–Si₃N₄ pair acted as FRET system to enhance the emission intensity of β-Si₃N₄ nanoparticles.     

Characterization of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles synthesized by various methods

Microwave-induced combustion with glycine, CTAB-assisted hydrothermal process with NaOH and NH3, EDTA assisted-hydrothermal methods have been applied to prepare NiFe₂O₄ nanoparticles for the first time. Structural and magnetic properties of the products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmison electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and electron spin resonance spectrometry (EPR). TEM measurements showed that morphology of the product depends on the synthesis method employed. The average cystallite size of NiFe₂O₄ nanoparticles was in the range of 14–59 nm as measured by XRD. The uncoated sample (Method A) had an EPR linewidth of 1973 Oe, the coated samples reached lower values. The magnetic dipolar interactions existing among the Ni ferrite nanoparticles are reduced by the coatings, which could cause the decrease in the linewidth of the EPR signals. Additionally, the linewidth increases with an increase in the size and the size distribution of nanoparticles.