Surface immobilisation of the sandwich type Na14[Fe4(Ox)4(H2O)2(SbW9O33)2]·60H2O polyoxometalate

A functionalised Fe-substituted Keggin Na₁₄[Fe₄(C₂O₄)₄(H₂O)₂(SbW₉O₃₃)₂]·60H₂O type POM termed “Fe₄Ox₄” has been successfully immobilised onto carbon electrode surfaces through the employment of conducting polypyrrole films and the layer-by-layer (LBL) technique. For the POM doped polypyrrole films the redox systems associated with the POM's tungsten-oxo framework was not apparent upon redox cycling, however a reversible redox couple associated with the Fe^III/II redox system was clearly seen within the pH range 2–7. Organised multilayer assemblies were constructed by the employment of the layer by layer (LBL) technique through alternating anionic Fe₄Ox₄ layers and cationic Ru^II metallodendrimers with poly(diallyldimethylammonium chloride) (PDDA) employed as an initial base layer. Stable redox couples associated with both the Fe^III/II and tungsten-oxo framework, for the Fe₄Ox₄ POM, and the Ru^III/II for the metallodendrimer, were clearly observed upon layer construction and redox switching within the pH domain of 2–7. The resulting multilayer assembly showed good stability towards redox cycling. Further investigations into the multilayer assembly were undertaken by determining it is charge transfer resistance using AC-impedance voltammetry. The layer also showed catalytic ability towards the reduction of H₂O₂ at pH 6.5.     

Possibility of Initiation of Combustion of CH4–O2 (Air) Mixtures with Laser‐Induced Excitation of O2 Molecules

The possibility of initiation of combustion of CH₄–O₂ mixtures with excitation of O₂ molecules to the states a¹_g and b¹⁺ _g by laser radiation with wavelengths of 1.268 m and 762 nm is considered. It is shown that excitation of O₂ molecules significantly decreases the induction period and ignition temperature because of accelerated formation of active atoms and radicals and intensification of the chain mechanism of the process. Even if the specific energy of laser radiation absorbed by the gas is low ( 0.1 eV per molecule), the ignition temperature of the CH₄–O₂ mixture with a ratio of 1:2 can be reduced from 1000 to 300 K.     

Hydrothermal synthesis, crystal structure and properties of complex [Co (odpa) (phen) 2 ( H2O )] · H2O

以4,4’-氧化二苯四羧酸二酐和1,10-邻菲啰啉为配体在水热条件下合成了标题配合物,并用元素分析、红外光谱、X-射线单晶衍射以及热重分析对配合物进行了表征.晶体结构分析表明配合物为三斜晶系,P-1空间群a=11.190(2)(A),b=12.587(2) (A),c=13.097(3)(A),α=102.688(3)°,β=105.751(2)°,γ =92.615(2)°,V =1721.1(6)A3,Z=2.配合物为单核结构,相邻的单核分子通过氢键的识别作用形成一维超分子双链.π…π堆积作用和C-H…π之间弱相互作用将邻近超分子双链的进一步扩展为三维超分子结构.     

Synthesis,structure and characterization of (NH4)2[Cu2(H2O)4(NH3CH2COO)2(NH2CH2COO)2]H2V10O28·6H2O

The decavanadate with a novel glycine–glycinato complex of copper (II) in the cationic part, (NH₄)₂[Cu₂(H₂O)₄(NH₃CH₂COO)₂(NH₂CH₂COO)₂]H₂V₁₀O₂₈·6H₂O (1), has been prepared and characterized by elemental analysis, infrared and EPR spectroscopies. The triplet X band EPR spectrum of powdered sample evidenced magnetic interaction between the Cu(II) atoms in the dimeric unit which is probably realized through the bridging water molecules in this part of the complex. A single crystal X-ray diffraction study revealed that the structure of 1 contains cationic copper complex with a rare Cu(H₂O)₂Cu double bridge. In this cation, a simultaneous bidentate N, O– and monodentate O– coordination of glycine to the same central atom was observed for the first time.     

Synthesis of an osmafuran from photochemical hydrolysis of OsCl2(CHC(PPh3)C(O)-η2-CHCH2)(PPh3)2

The η²-alkene coordinated α,β-unsaturated ketone complex Os(CHC(PPh₃)C(O)-η²-CHCH₂)Cl₂(PPh₃)₂ (3) is very stable even at elevated temperature due to the strong steric hindrance effect of PPh₃ ligands. However, compound 3 in a chloroform solution can be almost quantitatively converted into the corresponding osmafuran [OsCl(CO)(PPh₃)₂(CHC(PPh₃)C(CH₃)O)]Cl (6) via hydrolysis of the η²-coordinated olefin under photochemical conditions. Osmafuran 6 has been characterized by single crystal X-ray diffraction analysis, NMR spectroscopy and elemental analysis data. The UV-induced reaction provides a new highly efficient method for preparation of osmafurans by hydrolysis of η²-α,β-unsaturated ketone complexes.     

Terbium-oxalate-pyridinedicarboxylate coordination polymers suggesting the reductive coupling of carbon dioxide (CO2) to oxalate (C2O42−):[Tb2 (3,5-PDC)2(H2O)4(C2O4)]·2H2O and [Tb(2,4-PDC)(H2O)(C2O4)0.5] (PDC = pyridinedicarboxylate)

Under hydrothermal conditions, Tb(NO₃)₃·5H₂O reacted with 3,5-pyridinedicarboxylic acid (3,5-PDCH₂) to give a 3-D coordination polymer with the empirical formula of [Tb₂ (3,5-PDC)₂(H₂O)₄(C₂O₄)]·2H₂O (1). Tb(NO₃)₃·5H₂O also reacted with 2,4-pyridinedicarboxylic acid (2,4-PDCH₂) to give another 3-D coordination polymer [Tb₂ (2,4-PDC)₂(H₂O)₂(C₂O₄)] (2). The structures of both polymers have been determined by X-ray diffraction. X-ray structure analyses show that both polymers contain bridging oxalate (C₂O₄²⁻) ligands, which might have been formed by the reductive coupling of CO₂ molecules released from the PDC²⁻ ligands through the C–C bond cleavage.     

氯化钡(BaCl_2·2H_2O)

正1)性质。无色单斜晶系结晶。冷结晶为扁平菱形,热结晶为无定形。工业品为白色片状或粉状结晶。结晶水在空气中稳定,加热到113℃时失去结晶水。易溶于水,溶解度随温度的升高而增大。有乙醇及氯离子(如氯化钙)存在时,溶解度显著降低。在乙醇及酸中的溶解度比在水中的溶解度小。在无水乙醇中失去结晶水,但并不溶解。不溶于丙酮。氯化钡的水溶液具苦咸味,并且因含氯离子而具有较强的腐蚀性。工业氯化钡有毒、不易燃、不易爆。     

Electrical,structural and thermal properties of nanoceramic (Bi2O3)1−x−y(Ho2O3)x(Tm2O3)y ternary system

Ho₂O₃ and Tm₂O₃ doped Bi₂O₃ composite electrolyte type materials for solid oxide fuel cells (SOFCs) operating at intermediate-temperature were investigated. The bismuth-based ceramic powders were produced by using conventional solid-state synthesis techniques. The products were characterized by means of scanning electron microscopy (SEM), X-ray powder diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG), and the four-point probe technique (4PPT). XRD and DTA/TG measurements indicate that all of the samples have the stable fluorite type face centered cubic (fcc) δ-phase. 4PPT measurements were performed in the temperature range 150–1000 °C in air and these measurements showed that the electrical conductivity of the samples decrease with increasing amount of Tm₂O₃. This increase in the electrical conductivity of the samples could be attributed to the increase in the numbers of highly polarizable cations and oxide ion vacancies. The highest conductivity value was found as 5.31×10^?1 Ω cm^?1 for the (Bi₂O₃)_1?x?y(Ho₂O₃)_x(Tm₂O₃)_y ternary system (for x=20 and y=5 mol%) at 1000 °C. The activation energies of the samples were calculated from log σ graphics versus 1000/T. These calculated results showed that the translation motion of the charge carriers, oxygen vacancies, and space charge polarizations are responsible for the change in activation energy as a function of temperature.     

Microwave dielectric characteristics of 0.75(Al1/2Ta1/2)O2–0.25(Ti1−xSnx)O2 ceramics

The microwave dielectric characteristics of 0.75(Al_1/2Ta_1/2)O₂–0.25(Ti_1−xSn_x)O₂ ceramics were investigated. The microwave dielectric properties of 0.75(Al_1/2Ta_1/2)O₂–0.25TiO₂ sintered at 1450 °C exhibited a dielectric constant (ϵ_r) of 31.2, a Q·f₀ of 54,590 GHz, and the temperature coefficient of resonant frequency (τ_f) of +12.8 ppm/°C. To control of the τ_f and enhance the Q·f₀ for 0.75(Al_1/2Ta_1/2)O₂–0.25TiO₂, Sn⁴⁺ was substituted for Ti⁴⁺. With an increase of Sn content from 5 to 50 mol%, the ε_r slightly decreased, the Q·f₀ increased and the τ_f shifted from positive to negative value. The τ_f within ±10 ppm/°C of zero was realized for the Sn content below 30 mol% and the microwave dielectric properties had the ε_r value of 31.2–26.3, the Q·f₀ of 54,600–70,700 GHz, and τ_f of +12.8–−9.3 ppm/°C for this compositions. The relationship between microstructure and microwave dielectric characteristics was investigated.     

Synthesis,characterization and sorption properties of a porous coordination polymer: Co3(citrate)2(4,4′-bipyridine)4(H2O)2·4(H2O)

A porous coordination polymer, Co₃(citrate)₂(4,4^′-bipyridine)₄(H₂O)₂·4(H₂O) has been synthesized and characterized. It adopts a 3-D framework, built up by parallel [Co₃(citrate)₂]_n chains cross-linked by 4,4^′-bipyridine ligands. The connection leads to hydrophilic cavities filled with water molecules, which interact with the citrate ligands through hydrogen bonds. Dangling 4,4^′-bipyridine ligands are observed in the structure, pointing to cavities. Two equivalents of coordination water and four equivalents of crystallization water molecules can be removed reversibly based on TGA studies.     

Adsorption of Cr (VI) on synthetic hematite (α-Fe2O3) nanoparticles of different morphologies

The adsorption of Cr (VI) from aqueous solution onto nanoparticles hematite (α-Fe₂O₃) of different morphologies synthesized by acid hydrolysis, transformation of ferrihydrite, sol gel methods has been investigated. The hematite particle sizes were in the range 15.69-85.84 nm and exhibiting different morphologies such as hexagonal, plate-like, nano-cubes, sub-rounded and spherical. The maximum adsorption capacity of Cr (VI) was found to be in the range 6.33–200 mgg^?1 for all hematite samples. The kinetics of sorption was rapid, reaching equilibrium at 45–240 minutes. Sorption kinetics and equilibria followed pseudo-second order and Langmuir adsorption isotherm models. The rate constants were in the range 0.996–2.37×10^?2 g/mg/min for all samples. The maximum adsorption was attained at pH 3.0, while adsorption decreased as the pH increased from pH 3.0 to 10.0. The study revealed that the hematite with plate-like morphology has the highest adsorption capacity. The sorption process has been found to be feasible following a chemisorption process, and adsorption of Cr (VI) onto hematite nanoparticles was by inner sphere surface complexation due to low desorption efficiency in the range 9.54–53.4%. However, the result of ionic strength revealed that the reaction was by outer sphere complexation. This study showed that morphologies play a vital role in the adsorption capacities of samples of hematite in the removal of Cr (VI) from aqueous solution.     

A tetranuclear oxomolybdenum(V) complex with bridging squarate ligands, [MoV4O8(OH)2(H2O)2(C4O4)2]2−

The new tetranuclear polyoxomolybdate(V) ion [Mo^V₄O₈(OH)₂(H₂O)₂(C₄O₄)₂]²⁻ has been obtained in one step by the reaction of sodium molybdate, hydrazine and squaric acid in water and crystallized as a potassium salt. The structure has been solved by single-crystal X-ray diffraction showing the location of the hydroxo and water molecule ligands.     

Use of HPLC in the identification of cis and trans-diaquabis(2,2′-bipyridine)ruthenium(II) complexes: crystal structure of cis-[Ru(H2O)2(bpy)2](PF6)2

[Ru(H₂O)₂(bpy)₂](PF₆)₂ complex was obtained by reacting HPF₆ in a [Ru(CO₃)(bpy)₂] aqueous solution. The complex can exist as cis and trans isomers and usually has been used in the preparation of several ruthenium–bipyridine species. Despite the possibility to have contamination of a specie in another, there is no analytical control involving the characterization of both complexes. Based on this we have proposed the use of high-performance liquid chromatography (HPLC) as an analytical technique to control the purity of cis and trans isomers. The separation was performed using a CLC-ODS column. The cis isomer eluted at 9.4 min while trans isomer eluted at 4.3 min. In aqueous solution the trans and cis isomer configurations were confirmed by NMR spectra (¹H). The attribution of cis isomer was also made based on the X-ray crystal structure (monoclinic, P2_1/c, a=12.320(2), b=13.852(2), c=34.220(3) Å, β=91.89(1)°, Z=8) which is reported. The six-coordinated ruthenium atom is chelated by two bipyridines and two molecules of H₂O.     

(en)Mn2(V2O7): A 3D manganese vanadate built by Mn–O layers and two types of pillars of V2O7 and en bridges

An unexpected 3D manganese vanadate (en)Mn₂(V₂O₇) (1) (en = ethylenediamine) has been hydrothermally obtained by H₂E₂Ge₂O₃ (E = ? CH₂CH₂COO^?) ligands and well-prepared mixture of V–Mn-amine and characterized by IR spectroscopy, elemental analysis, thermal stability and powder X-ray diffraction. Single-crystal X-ray diffraction analysis reveals that the structure is a novel pillared-layer, in which MnO₅N octahedra are corner-linked to form an infinite sheet with 4-membered rings (MRs) and further condensed to the 3D framework. The most prominent feature of 1 is the connection between the sheets via double bridges, namely, inorganic V₂O₇ dimeric units and organic en molecules. It is noteworthy that inorganic and organic double bridges between sheets have not been seen in manganese vanadates.     

Suppressing fire hazard of poly(vinyl alcohol) based on (NH4)2[VO(HPO4)]2(C2O4)·5H2O with layered structure

Two-dimensional layered ammonium vanadium oxalate-phosphates (AVOPh) with the structural formula of (NH₄)₂[VO(HPO₄)]₂(C₂O₄)·5H₂O are synthesized though a hydro-thermal method, which is dispersed into poly(vinyl alcohol) (PVA) matrix to prepare PVA/AVOPh composites. The results of thermal analysis indicate that AVOPh and PVA have similar decomposition temperature from 280 to 500°C, which is critical for choosing flame retardant. The incorporation of AVOPh significantly improves the thermal stability and flame retardancy of PVA/AVOPh composites that the T_5% value of PVA/2 wt% AVOPh composites is up to 215°C, and the residue of PVA/8 wt% AVOPh composites is enhanced to 16.9%, while those of pure PVA are only 178°C and 2.4%. PVA/4 wt% AVOPh composites can pass V-0 level, and its limiting oxygen index value is up to 32.0%. Furthermore, the peak heat release rate (PHRR) and total heat release (THR) of PVA/AVOPh composites are obviously decreased, which reduced by 43.4% and 43.8% with the addition of 4 wt% AVOPh, compared with those of pure PVA. The excellent thermal stability and flame retardancy are mainly attributed to the uniform dispersion and barrier effect of 2D layered AVOPh, the release of crystal water, ammonia and phosphorus free radicals and the two-phase flame retardant catalytic mechanism of vanadium and phosphorus.     

Low temperature Mössbauer spectroscopic study of CaO(Fe2O3)1−x(Al2O3)x system

Low temperature ⁵⁷Fe Mössbauer spectroscopic studies on CaO(Fe₂O₃)_1−x(Al₂O₃)_x, written as CF_1−xA_x, have been carried out. In view of the earlier findings based on room temperature data, the spectra have been analysed by assuming three Fe sites: two belonging to CF phase and the third site for the Fe atoms distributed in the CA phase. The Fe sites pertaining to the CF phase experience hyperfine field of about 49T and 47T, respectively, at 20K; whereas the third site is paramagnetic at this temperature.