A one-dimensional barium(II) coordination polymer with a coordinated nitro group of 2-nitrobenzoate

The aqueous reaction of barium carbonate with 2-nitrobenzoic acid (2-nbaH) results in the formation of a one-dimensional coordination polymer, catena-poly[[hexa(aqua)dibarium(II)]bis[(μ ₂-2-nitrobenzoate-O,O,O-NO₂)(μ ₂-2-nitrobenzoate-O,O,O′)]] 1. On heating at 100°C compound 1 is dehydrated to anhydrous barium bis(2-nitrobenzoate) 2. The anhydrous compound can be re-hydrated to 1 on exposure to water vapour. Compounds 1 and 2 were characterized by elemental analysis, IR and UV-Vis spectra, DSC thermograms, weight loss studies and the structure of 1 was determined. 1 and 2 can be thermally decomposed to BaCO₃ by heating at 800°C. The polymer [[Ba(H₂O)₃]₂(μ ₂-2-nba-O,O,O-NO₂)₂ (μ ₂-2-nba-O,O,O′)₂] _n 1 crystallizes in the centrosymmetric triclinic space group Pī and all atoms are located in general positions. The polymeric structure is based on a dimeric unit and consists of three water molecules coordinated to a central Ba(II) and two unique 2-nitrobenzoate (2-nba) anions, one of which (μ ₂-2-nba-O,O,O-NO₂) functions as a tridentate ligand and is linked to a Ba(II) through the oxygen atom of the-NO₂ group and forms a monoatomic μ ₂-carboxylate bridge between two symmetry related Ba(II) ions with a Ba···Ba distance of 4·5726(14) ?. The second unique 2-nba anion (μ ₂-2-nba-O,O,O′) also functions as a tridentate ligand with the carboxylate oxygen atoms linked to a Ba(II) ion in a bidentate fashion and one of the carboxylate oxygen atoms forming a monoatomic bridge between two symmetry related Ba(II) ions resulting in a Ba···Ba separation of 4·5406(15) ?. These differing tridentate 2-nba ligands link {Ba(H₂O)₃} units into a one-dimensional polymeric chain extending along b axis. In the infinite chain each nine coordinated Ba(II) is bonded to three water molecules and further linked to six oxygen atoms of four different 2-nitrobenzoate anions with alternating pairs of Ba(II) ions in the chain bridged by a pair of (μ ₂-2-nba-O,O,O-NO₂) and (μ ₂-2-nba-O,O,O′) ligands resulting in alternating Ba···Ba distances of 4·5406(15) and 4·5726(14) ? across the chain. Dedicated to Prof. S. K. Paknikar on the occasion of his 73rd birthday.     

空气中合成固溶体荧光粉Ba_2(Zn,Mg)Si_2O_7∶Eu~(2+),Eu~(3+),Ce~(3+)及其发光特性

采用高温固相法在空气中合成了Ba1.97-yZn1-xMgxSi2O7∶0.03Eu,y Ce3+系列荧光粉。分别采用X-射线衍射和荧光光谱对所合成荧光粉的物相和发光性质进行了表征。在紫外光330~360 nm激发下,固溶体荧光粉Ba1.97-yZn1-xMgxSi2O7∶0.03Eu的发射光谱在350~725 nm范围内呈现多谱峰发射,360和500 nm处有强的宽带发射属于Eu2+离子的4f 65d1-4f 7跃迁,590~725 nm红光区窄带谱源于Eu3+的5D0-7FJ(J=1,2,3,4)跃迁,这表明,在空气气氛中,部分Eu3+在Ba1.97-yZn1-xMgxSi2O7基质中被还原成了Eu2+;当x=0.1时,荧光粉Ba1.97Zn0.9Mg0.1Si2O7∶0.03Eu的绿色发光最强,表明Eu3+被还原成Eu2+离子的程度最大。当共掺入Ce3+离子后,形成Ba1.97-yZn0.9Mg0.1Si2O7∶0.03Eu,y Ce3+荧光粉体系,其发光随着Ce3+离子浓度的增大由蓝绿区经白光区到达橙红区;发现名义组成为Ba1.96Zn0.9Mg0.1Si2O7∶0.03Eu,0.01Ce3+的荧光粉的色坐标为(0.323,0.311),接近理想白光,是一种有潜在应用价值的白光荧光粉。讨论了稀土离子在Ba2Zn0.9Mg0.1Si2O7基质中的能量传递与发光机理。     

A study of YBa2(Cu1?xMex)3O6 + δ (Me = Al, Co, Fe) electrophysical and electrochemical properties

The structure, thermal expansion coefficient, and electroconductivity of YBa₂(Cu_1−x Al _x )₃O_6+δ (x = 0.0–0.9) were studied at 20 to 900°C in air. The most conducting compositions of YBa₂(Cu_1−x Me _x )₃O_6+δ (Me = Al, Co, Fe) were determined. The electrochemical activity of electrodes with the most conducting compositions of YBa₂(Cu_1−x Me _x )₃O_6+δ (Me = Al, Co, Fe) was studied in a wide polarization range in the contact with 0.9ZrO₂ + 0.1Y₂O₃ solid electrolyte in air at the temperatures of 700 to 900°C. Original Russian Text ? V.K. Gil’derman, I.D. Remez, 2009, published in Elektrokhimiya, 2009, Vol. 45, No. 5, pp. 612–615. Published by report at IX Conference “Fundamental Problems of Solid State Ionics”, Chernogolovka, 2008.     

Ti3C2Tx/MnO2正极在水系锌电池中的电化学性能

二氧化锰(MnO₂)材料具有比容量大、电极电位高、储量丰富以及价格低廉等优势,成为水系锌电池正极最受关注的一类材料,然而其仍然存在着结构稳定性差和电化学储存机理复杂的问题。因此,我们通过两步合成法制备了一种花苞状结构的MnO₂负载在Ti₃C₂T_x表面形成Ti₃C₂T_x/MnO₂复合材料,通过X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)对复合样品的结构、成分和形貌进行表征。通过将Ti₃C₂T_x/MnO₂复合材料作为正极,与锌负极匹配组装成水系锌电池,研究了其分别在2 mol·L^-1 ZnSO₄、2 mol·L^-1 ZnSO₄+0.1 mol·L^-1 MnSO₄、30 mol·L^-1三氟甲基磺酸四乙基铵(TEAOTf)+1 mol·L^-1三氟甲烷磺酸锌(ZnOTf)和3 mol·L^-1 ZnOTf四种电解液中的电化学性能。结果表明,Ti₃C₂T_x/MnO₂在2 mol·L^-1 ZnSO₄中的比容量较高,但循环稳定性很差。将TEAOTf盐和ZnOTf盐共溶于水中,设计了一种新型的含惰性阳离子的超高浓度盐包水电解液(30 mol·L^-1 TEAOTf+1 mol·L^-1 ZnOTf),不仅提高了Ti₃C₂T_x/MnO₂材料的可逆性,而且有效抑制了电极材料在循环过程中的溶解。     

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。     

Structural and spectroscopic characterization of Al2−x Cr x O3 powders obtained by polymeric precursor method

Al₂O₃ and Al_2−x Cr _x O₃ (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL^*a^*b^* color data). The obtained results allow to identify the γ-Al₂O₃ to α-Al₂O₃ phase transition. The single-phase α-Al₂O₃ powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al_2−x Cr _x O₃ are related to the γ to α-Al₂O₃ phase transition and the temperature and time range for such transition depends on the chromium content.     

二维层状Ti3C2Tx-MXene@VS2用于高性能锂离子电池负极

为探索一种高性能的锂离子电池负极材料,采用酸刻蚀法制备了高导电性、高稳定性的二维层状Ti₃C₂T_x,通过溶剂热法制备了具有高理论比容量的花瓣状VS₂纳米片,再经过简单的液相混合得到了二维层状Ti₃C₂T_x-MXene@VS₂复合物。通过扫描电子显微镜、透射电子显微镜、X射线光电子能谱、X射线衍射和能谱分析对复合材料的形貌和结构进行了表征,采用循环伏安、恒流充放电、长循环和交流阻抗谱对复合材料的电化学性能进行了研究。结果表明：VS₂纳米片均匀地分布在Ti₃C₂T_x的层间及表面,该复合物具有高的可逆容量(电流密度为0.1A·g^-1时,比容量为610.5mAh·g^-1)、良好的倍率性能(电流密度为2A·g^-1时,比容量为197.1mAh·g^-1)和良好的循环稳定性(电流密度为0.2 A·g^-1时,循环600圈后比容量为874.9 mAh·g^-1;电流密度为2 A·g^-1时,循环1 500圈后比容量为115.9mAh·g^-1)。     

Theoretical study on H2 elimination pathways of silylenoid H2SiLiF with CH4, NH3, H2O, HF, SiH4, PH3, H2S, and HCl

Ab initio molecular orbital calculations have been performed to explore the reaction potential energy surfaces of silylenoid H₂SiLiF with XH _n hydrides, where XH _n = CH₄, NH₃, H₂O, HF, SiH₄, PH₃, H₂S, and HCl. We have identified a previously unreported reaction pathway on each reaction surface, H₂SiLiF + H-XH _{n − 1} → H _n XSiLiF + H₂, which involves H₂ elimination following the initial formation of an association complex via a four-membered ring transition state to form the substituted three-membered ring silylenoid H _n XSiLiF and a H₂ molecule. This theoretical calculations suggest that (i) for H₂ eliminations there is a very clear trend toward lower activation barriers and more exothermic interactions on going from left to right along a given row in periodic table, and (ii) for the second-row hydrides, the H₂ elimination reactions are less exothermic than for the first-row hydrides and the reaction barriers are lower for X–S and Cl. Compared to the insertions of H₂SiLiF into XH _n , the H₂ elimination pathways should be unfavorable with higher barrier and lower exothermic.     

Sodium and silver phosphate glasses doped with chlorides of Fe,Mn and Zn

A number of samples of sodium and silver phosphate glasses doped with various compositions of some transition metals viz. iron, manganese and zinc chlorides alongwith undoped samples of sodium and silver phosphate glasses were synthesized and characterized by X-ray diffraction, IR spectral, electrical conductivity and differential scanning calorimetry (DSC). The glass transition temperature (T _g) and crystallization temperature (T _c) values obtained from DSC curves were found to increase with increasing concentration of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses and the following sequence is observed: T _g(–FeCl₃)>T _g(–MnCl₂)>T _g(–ZnCl₂) T _c(–FeCl₃)>T _c(–MnCl₂)>T _c(–ZnCl₂) The increase in T _g and T _c values indicate enhanced chemical durability of the doped glasses. The electrical conductivity values and the results of FTIR spectral studies have been correlated with the structural changes in the glass matrix by the addition of different transition metal cations as dopants.     

Study of the selectivity of a V2O5?ZrO2 catalyst for partial oxidation ofo-xylene at high temperatures

It has been established that at high temperatures (above 450°C) the V₂O₅−ZrO₂ catalyst exhibits a higher selectivity in the oxidation ofo-xylene to phthalic anhydride than does the conventional V₂O₅−TiO₂(a) catalyst. The catalyst selectivity is found to increase with respect to partial oxidation ofo-xylene, the valuable by-product maleic anhydride being obtained. Studies by different physicochemical methods have shown that V₂O₅−ZrO₂ undergoes no significant phase and structural changes under high-temperature conditions.     

Electrochemical reduction of NO on La2-x Sr x NiO4 based electrodes

The series La_2 − x Sr _x NiO₄ (x = 0.0, 0.05, 0.15, 0.25, 0.35, and 1.0) was tested for functionality as electrode materials for direct electrochemical reduction of NO. The materials were tested using cyclic voltammetry in 1% NO and 10% O₂ in Ar on a cone-shaped electrode. The best materials for the electrochemical reduction of NO are La₂NiO₄ and LaSrNiO₄, which have current densities for NO reduction 1.82 and 7.09 times higher, respectively, than for O₂ at 400 °C. Increasing the temperature decreased the ability to reduce NO before O₂ while the activity increased. The adsorbed species during direct decomposition was attempted, clarified using X-ray absorption near-edge structure experiments and thermogravimetry, but no conclusive results were obtained.     

Comparative study of structural stability in [NH4−n (CH3) n ]2HgCl4 and in related compounds

The structural instability of the [NH_4−n (CH₃) _n ]₂HgCl₄ group has been investigated. Consideration of different crystals of this family shows that the H-bonds, obviously, hinder the appearance of incommensurate modulation. The dependence of phase transition sequence on the sizes of cation and anion may be obtained only for crystals with simple cation. The appearance of H-bonds complicates the situation and, leads to gradual disappearance of IC phase in the A₂BX₄ family.     

Nitrite formation in aerated aqueous azide solutions: A radiation chemical study

Gamma radiolysis of oxygenated 1–10 mM azide solutions was carried out at various pH values. In oxygenated 10 mM azide solutions, H₂O₂ and NO ₂ ⁻ were observed as radiolytic products while NH3 was not. The concentration of H₂O₂ reached its maximum level at a dose of 1 kGy, whereas NO ₂ ⁻ yield increased non-linearly beyond 2 kGy in this system. Both in aerated and oxygenated systems, G(NO ₂ ⁻ ) and G(H₂O₂) were found to vary with N ₃ ⁻ concentration. The yield of NO ₂ ⁻ was found to be dependent on both dose rate and pH. On pulse radiolysis, NO ₂ ⁻ was found as a radiolytic product in aerated 1 mM azide solution at pH 6.8. In this system the intermediate generated exhibits absorbance around 250 nm. The overall results obtained during the present study reveal that in presence of both reducing radical (mainly e _aq ⁻ ) and oxygen, N ₃ ⁻ produced an intermediate possibly NH₂O ₂ ^• radical, which is the prime source for NO ₂ ⁻ generation.     

The group-theoretical structure of the atomic g shell: connection with the alternating group <Emphasis Type="Italic">A</Emphasis><Subscript>6</Subscript> as <Emphasis Type="Italic">L</Emphasis><Subscript>2</Subscript>(9)

The special projective linear groups PSL(2ℓ + 1) or L ₂(2ℓ + 1) of order 2ℓ(2ℓ + 1)(ℓ + 1) can be used to study atomic shells of electrons with angular momentum quantum number ℓ corresponding to the atomic p, d, f, and g shells for ℓ = 1, 2, 3, 4, respectively. For the atomic g shell the group L ₂(9) is isomorphic with the alternating group A ₆ on six objects of order 360 or the symmetry group of the 5-dimensional simplex, a 5-dimensional analogue of the tetrahedron with 6 vertices and 15 edges. This leads to the subgroup chain SO(9) ⊃ SO(5) ⊃ L ₂(9) for the atomic g shell analogous to the subgroup chain SO(7) ⊃ G ₂ ⊃ L ₂(7) ≈⁷ O for the atomic f shell. In the L ₂(9) group only the representations of spherical harmonics or sums thereof, Γ(Y_ℓ), with dimensions dim Γ(Y_ℓ) or dim Γ(Y_ℓ) ± 1 divisible by 9 are found to be individually reducible to irreducible representations (irreps) or sums of irreps of L ₂(9). This leads to term groupings such as S, PD, G, PF, DH, L, PK, DI, FH, M, FI, PO, DN, HK, R, etc., of increasing total dimension for the irreps of SO(9) for various g ⁿ configurations in the atomic g shell.     

Etude des systemes CaHPO4−MHPO4−H2O (M=Sr,Ba) A 50°C

The systems CaHPO₄−MHPO₄−H₂O (M=Sr, Ba) were studied at 50°C. ForM=Sr, the series of single phases, Ca_1−xSr_xHPO₄ for 0.95<X<0.75 and Ca_xSr_1−xHPO₄ for 0.4<X<1 have been prepared. These solid solution were caracterized by their infrared spectra and their crystallographic unit cell parameters. ForM=Ba a new phase Ca₂Ba(HPO₄)₃ has been determined. It was characterized by DRX, IR, ATD and chemical analyses.

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Zusammenfassung Bei 50°C wurde das System CaHPO₄−MHPO₄−H₂O (mitM=Sr, Ba) untersucht. FürM=Sr wurden Serien von Einzelphasen erhalten: Ca_1−xSr_xHPO₄ für 0.95<X< 0.75 und Ca_xSr_1−xHPO₄ für 0.4<X<1. Diese Mischkristalle wurden anhand ihrer Infrarotspektren und ihrer kristallographischen Elementarzellenparameter charakterisiert. FürM=Ba wurde die neue Phase Ca₂Ba(HPO₄)₃ ermittelt. Sie wurde mittels DRX, IR, ATD und chemischer Analyse charakterisiert.

     

Electrochemical reduction of NO and O2 on La2−x Sr x CuO4-based electrodes

A series of La_2 − x Sr _x CuO₄ (x = 0.0, 0.05, 0.15, 0.25 and 0.35) compounds was investigated for the use of direct electrochemical reduction of NO in an all-solid-state electrochemical cell. The materials were investigated using cyclic voltammetry in 1% NO in Ar and 10% O₂ in Ar. The most selective electrode material was La₂CuO₄, which had an activity of NO reduction that was 6.8 times higher than that of O₂ at 400 °C. With increasing temperature, activity increased while selectivity decreased. Additionally, conductivity measurements were carried out, and the materials show metallic conductivity behavior which follows an adiabatic small polaron hopping mechanism.     

The NiFe2O4 - MgFe2O4 series as electrode materials for electrochemical reduction of NO x

Solid solutions of spinel-type oxides with the composition (x = 0.0, 0.3, 0.5, 0.6, 1.0) were prepared with the glycine-nitrate combustion synthesis (x = 0.0, 0.3, 0.5, 0.6) and the citric-acid combustion synthesis (x = 1.0). The oxides were used as electrode materials in a pseudo-three-electrode setup in the temperature range of 400–600 °C. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the electrochemical behavior in 1% NO and 10% O₂. Measurements show that NiFe₂O₄ has relatively high cathodic activity in both NO and O₂, whereas MgFe₂O₄ shows much higher activity in NO compared to O₂. MgFe₂O₄ was also measured with cyclic voltammetry in 1% NO₂ and different gas mixtures of NO and O₂ at 300 and 400 °C. Results show that the cathodic activities (−0.6 V) are relatively high with current ratios, , ranging from 10.1–167.7 and with a maximum at 400 °C. Dilatometry measurements were performed on the materials in air up to 1,000 °C, and they showed that the Curie temperature could be detected for all samples. Four-point DC resistivity measurements at elevated temperatures show that Ni_0.4Mg_0.6Fe₂O₄ has the highest conductivity, whereas Ni_0.7Mg_0.3Fe₂O₄ and NiFe₂O₄ have the highest conductivity at lower temperatures.     

Chemistry of ruthenium in N2P2X2 (X = Cl, Br) coordination sphere: Synthesis, characterization and reactivities

Reaction of 2-(phenylazo)pyridine (pap) with [Ru(PPh₃)₃X₂] (X = Cl, Br) in dichloromethane solution affords [Ru(PPh₃)₂(pap)X₂]. These diamagnetic complexes exhibit a weakdd transition and two intense MLCT transitions in the visible region. In dichloromethane solution they display a one-electron reduction of pap near − 0.90 V vs SCE and a reversible ruthenium(II)-ruthenium(III) oxidation near 0.70 V vs SCE. The [Ru^III(PPh₃)₂(pap)Cl₂]⁺ complex cation, generated by coulometric oxidation of [Ru(PPh₃)₂(pap)Cl₂], shows two intense LMCT transitions in the visible region. It oxidizes N,N-dimethylaniline and [Ru^II(bpy)₂Cl₂] (bpy = 2,2′-bipyridine) to produce N,N,N′,N′-tetramethylbenzidine and [Ru^III(bpy)₂Cl₂]⁺ respectively. Reaction of [Ru(PPh₃)₂(pap)X₂] with Ag⁺ in ethanol produces [Ru(PPh₃)₂(pap)(EtOH)₂]²⁺ which upon further reaction with L (L = pap, bpy, acetylacetonate ion(acac⁻) and oxalate ion (ox²⁻)) gives complexes of type [Ru(PPh₃)₂(pap)(L)]ⁿ⁺ (n = 0, 1, 2). All these diamagnetic complexes show a weakdd transition and several intense MLCT transitions in the visible region. The ruthenium(II)-ruthenium(III) oxidation potential decreases in the order (of L): pap > bpy > acac⁻ > ox²⁻. Reductions of the coordinated pap and bpy are also observed.     

Voltammetric determination of the trace amounts of bromate in drinking water after pre-concentration on hydrous γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

A differential pulse voltammetric (DPV) method for the determination of bromate in drinking water, after pre-concentration on γ-Al₂O₃, is proposed. The reduction peak of bromate has been observed at the potential E _p -−1.6 V in an ammonia buffer as a supporting electrolyte. The method has been successfully applied to determine a bromate concentration of 2.5 μg·l⁻¹ in drinking water (RSD=6.1%, n=7). A sample pre-treatment with a column filled with mixed cation-exchange resin in Ag, Ba and H forms was needed before pre-concentration of bromate on alumina.