Synthesis and structures of some sterically hindered zinc complexes containing 6-membered and rings

Zinc β-diketiminates containing the N,N′-chelating ligand [{N(SiMe₃)C(Ph)}₂CH]⁻ (≡LL⁻) [Zn(LL)(μ-Cl)]₂ (1) and [ZnEt(LL)thf] (2) were prepared from 2ZnCl₂ + [Li(LL)]₂ and ZnEt₂ + H(LL), respectively. The new phenols 2-(N-R-piperazinyl-N′-methyl)-4,6-di-tert-butylphenol [R = Ph (3a), Me (3b)] and 2,2-[μ-N,N′-piperazindiyldimethyl]-bis(4,6-di-tert-butylphenol) (4) were obtained from 2,4-tBu₂C₆H₃OH, (CH₂O)_n and the appropriate piperazine. Zinc phenoxides 5, 7 and 8 were derived from 2ZnEt₂ with 2(3a), 2(3b) and 4, respectively. Controlled methanolysis of 5 furnished the bis(phenoxo)zinc compound Zn[OC₆H₂tBu₂-2,4-{CH₂N(CH₂CH₂)₂NPh}-6]₂ (6). The X-ray structures of the crystalline zinc compounds 1, 2, 5, 6, 7 and 8, are presented; each of 5-8 contains two six-membered rings. The centrosymmetric molecule 1 has a rhomboidal (ZnCl)₂ core with exceptionally different Zn-Cl and Zn-Cl′ bond lengths of 2.248(1) and 2.509(1) Å, respectively. None of 1, 2 or 5-8 was an effective catalyst for the copolymerisation of an oxirane and CO₂.     

Nickel-aluminum layered double hydroxides prepared via inverse micelles formation

Nickel-aluminum layered double hydroxides have been prepared by conventional coprecipitation and by coprecipitation in the presence of a surfactant. The solids have been characterised by several physicochemical techniques. Calcination leads to formation of homogeneously dispersed mixed oxides, which have been characterised as well. The colour properties (lightness and chromaticity coordinates) of both series of solids (layered precursors and calcined ones) have been measured. It has been found that both the preparation method and the calcination treatment have an important effect on the luminosity (whiteness/darkness) of the solids, although the effect on the precise chromaticity coordinates (green/red and blue/yellow) is less marked.     

Investigation of thermal transformations in aluminium hydroxides subjected to mechanical treatment

The influence of the mechanical activation of hydrargillite Al(OH)₃ on the mechanism of its' thermal dehydration and crystallization in response to treatment with steam was studied. The effects of grinding on the texture, structure and thermal behavior were examined by means of XRD, DTA, TG, DSC, IR spectroscopy and SEM. The mechanical activation of hydrargillite leads to formation of the amorphous state, and also results in a change in the thermal dehydration mechanism in the dynamic mode in the air, with a decrease in the H value of dehydration. The transition of hydrargillite into corundum on treatment with steam is facilitated after mechanical activation. The activated state of hydrargillite was found to be unstable and its reactivity decreases as time elapses.     

Rhodium carbonyl complexes of bulky, anionic nitrogen-based ligands: A comparison of donating ability

Phosphinimine-imine ((C₆H₃i-Pr₂)NC(Me)CH₂PPh₂(NC₆H₃i-Pr₂))Rh(CO)₂ - (1) and β-diketiminate CH(C(Me)(Ni-Pr₂C₆H₃))₂Rh(CO)₂ - (2) rhodium dicarbonyl complexes were prepared as to elucidate any difference among these anionic, nitrogen-based ligands regarding donating ability to the rhodium center. Utilizing infrared spectroscopy and single crystal structural comparisons, differences in electron density donation by the ligands to the rhodium center were not observed. The carbonyl stretching frequencies of the aforementioned rhodium complexes were ν_CO = 2055, 1987 and 2055, 1988 for the phosphinimine-imine (1) and β-diketiminate (2) respectively.     

硫掺杂镍铁层状双氢氧化物的氧析出电催化性能

氧析出反应(OER)是裂解水、二氧化碳还原、以及可充电的锌空电池等许多技术中重要的半反应,但受限于其迟缓的反应动力学,开发高效的氧析出催化剂迫在眉睫.在OER出反应中,性能较好的非贵金属催化剂主要是第四周期过渡金属的一些化合物,如氧化物、氢氧化物、硫化物、硒化物、磷化物等等.在这些材料中,镍铁双金属化合物被认为是最优的氧析出材料,尤其是镍铁层状双氢氧化物(Ni Fe-LDHs)它拥有较大的电化学活性面积以暴露较多活性位点,同时镍铁两种过渡金属元素存在协同效应,使得其具有良好的催化性能.然而,这一类材料的OER性能仍然有优化的空间.研究表明,将硫化物氧化得到的氢氧化物会有少量的硫元素残留,这种硫残留的氢氧化物拥有十分优异的OER性能.为了进一步认识硫的引入对Ni Fe-LDHs的OER行为的影响,本文通过水热法合成了硫掺杂的Ni Fe-LDHs,考察了硫的掺杂量对催化剂性能的影响,验证了微量硫的存在对Ni Fe-LDHs的OER性能的贡献.扫描电镜图片显示,水热合成的催化剂是厚度为几十纳米的薄片,拥有较高的比表面积, X射线荧光光谱分析证明合成的硫掺杂Ni Fe-LDHs中镍铁的元素比例为4:1,而且硫的掺杂量并不影响催化剂的形貌和其中镍铁元素比.X射线光电子能谱分析表明,硫原子的引入使得铁原子结合能降低,即硫与铁的相互作用部分降低了铁的价态,这种硫和铁的相互作用能够优化OER反应中间体OH*与O*在铁活性位点上的吸附自由能,降低氧析出反应的过电势.电化学测试表明,拥有0.43%的硫掺杂Ni Fe-LDHs拥有最好的氧析出性能, 10 m A cm^-1下超电势仅有257 m V, Tafel斜率61.5 m V dec^-1.此后,随着硫掺杂量的提升,其性能先保持稳定,随后有所下降.在稳定测试中,硫掺杂的镍铁层状双氢氧化物在10 m Acm-1电流密度下循环30 h后过电位仅衰减14 m V.在对稳定性测试后的催化剂进行表征表明,催化剂发生了轻微了变形,但这对性能的影响不大.综上,本文提供了一种简便的通过非金属元素掺杂调控过渡金属氧化物的结构和电子态的方法,有望为设计高活性OER电催化剂提供新思路.     

New route to ABCD-porphyrins via bilanes

A new strategy for preparing porphyrins that bear up to four different meso-substituents (ABCD-porphyrins) relies on two key reactions. One key reaction entails a directed synthesis of a 1-protected 19-acylbilane by acid-catalyzed condensation at high concentration (0.5 M) of a 1-acyldipyrromethane and a 9-protected dipyrromethane-1-carbinol (derived from a 9-protected 1-acyldipyrromethane). Three protecting groups (X) were examined, including thiocyanato, ethylthio, and bromo, of which bromo proved most effective. The bilanes were obtained in 72-80% yield, fully characterized, and examined by 15N NMR spectroscopy. The second key reaction entails a one-flask transformation of the 1-protected 19-acylbilane under basic, metal-templating conditions to give the corresponding metalloporphyrin. The reaction parameters investigated for cyclization of the bilane include solvent, metal salt, base, concentration, temperature, atmosphere, and time. The best conditions entailed the 1-bromo-19-acylbilane at 100 mM in toluene containing DBU (10 mol equiv) and MgBr2 (3 mol equiv) at 115 degrees C exposed to air for 2 h, which afforded the magnesium porphyrin in 65% yield. The magnesium porphyrin is readily demetalated to give the free base porphyrin. A stepwise procedure (which entailed treatment of the 1-(ethylthio)-19-acylbilane to oxidation, metal complexation, desulfurization, carbonyl reduction, and acid-catalyzed condensation) was developed but was much less efficient than the one-flask process. The new route to ABCD-porphyrins retains the desirable features of the existing "2 + 2" (dipyrromethane + dipyrromethane-1,9-dicarbinol) method, such as absence of scrambling, yet has significant advantages. The advantages include the absence of acid in the porphyrin-forming step, the use of a metal template for cyclization, the ability to carry out the reaction at high concentration, the lack of a quinone oxidant, avoidance of use of dichloromethane, and the increased yield of macrocycle formation to give the target ABCD-metalloporphyrin.     

Formation of YAG from coprecipitated yttrium aluminium hydroxides

Thermal decomposition of the amorphous coprecipitate of yttrium and aluminium hydroxides forming yttrium aluminium garnet has been investigated employing thermal analyses, X-ray diffraction and IR spectroscopy. On heating, the coprecipitate progressively loses water forming a stable but highly disordered hydroxy garnet which crystallizes at 1180 K and decomposes to YAG at 1290 K. Nucleation of the crystalline phase appears to begin at 800 K.The authors thank Dr. P. V. Ravindran of the Analytical Chemistry and Shri N. K. Kulkarni of the Fuel Chemistry Divisions of BARC for their assistance in the thermoanalytical experiments.     

Synthesis and intracrystalline oxidation of nitrite-intercalated layered double hydroxides

Nitrite-intercalated LDHs could be prepared by a two-stage process that involves coprecipitation in the presence of nitrite ions followed by stirring the product with excess of nitrite ions. The nitrite ion lies flat in these LDHs with its c₂-axis lying approximately perpendicular to the crystallographic c-axis. The interlayer nitrite ions in these LDHs could be quantitatively oxidized to nitrate ions using H₂O₂ solution. In the LDHs thus obtained the nitrate ion lies flat with its c₃-axis parallel to the crystallographic c-axis (D_3h symmetry) in the interlayer region resulting in lower basal spacing.     

Direct decarbonation of micrometer-scale layered double hydroxides without morphology damage

A direct decarbonation route without obvious morphology damage was developed for large micrometer-scale layered double hydroxides（LDHs）.First,we synthesized pure,hexagonal-shaped LDHs with lateral dimension of micrometer-size by the recently reported urea hydrolysis method.Then,using HNO₃-NaNO₃ mixed solution,the obtained LDH with carbonate anions in the interlayer（LDH_CO₃） was directly decarbonated to its nitrate form,LDH_NO₃,its morphology and particle size were still unchanged.Compared with the recently published two-step decarbonation method,the direct decarbonation reported herein is very convenient.     

Synthesis and characterization of a β-diketiminate-supported aluminum dication

A base-stabilized mononuclear aluminum dication has been prepared by extrusion of two triflate anions from a precursor β-diketiminate-supported aluminum bis(triflate) using the tris(2-aminoethyl)amine (tren) ligand.     

A study on the thermal decomposition of iron-cobalt mixed hydroxides

Thermal decomposition of pure Fe(OH)₃ and mixed with Co(OH)₂ were studied using TG, DTA, kinetics of isothermal decomposition and electrical conductivity measurements. The thermal products were characterized by X-ray diffraction and IR spectroscopy. The TG and DTA analysis revealed the presence of Co²⁺ retards the decomposition of ferric hydroxide and the formation of -Fe₂O₃. The kinetics of decomposition showed that the mixed samples need higher energy to achieve thermolysis. The investigation of thermal products of mixed samples indicated the formation of cobalt ferrite on addition ofx=1 or 1.5 cobalt hydroxide. The electrical conductivity accompanying the thermal decomposition decreases in presence of low ratio of Co²⁺ (x=0.2) via the consumption of holes created during thermal analysis. The continuous increase in values on increasing of Co²⁺ concentration corresponded to the electron hopping between Fe²⁺ and Co³⁺.

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Zusammenfassung Mittels TG, DTA und der Kinetik von Messungen der isothermen Zersetzung und der elektrischen Leitfähigkeit wurde die Zersetzung von Fe(OH)₃ in reinem Zustand und vermengt mit Co(OH)₂ untersucht. Die thermischen Produkte wurden mittels Röntgendiffraktion und IR-Spektroskopie charakterisiert. TG und DTA zeigen, daß die Zersetzung von Eisen(III)-hydroxid und die Bildung von -Fe₂O₃ durch Gegenwart von Co²⁺ verzögert wird. Die Zersetzungskinetik zeigt, daß die Mischproben mehr Energie für die Thermolyse benötigen. Die Untersuchung der thermischen Produkte zeigt die Bildung von Cobaltferrit bei Zusatz vonx=1 oder 1,5 Cobalthydroxid. Die elektrische Leitfähigkeit nimmt bei der thermischen Zersetzung in Gegenwart von niedrigen Co²⁺-Konzentrationen (x=0.2) durch Verbrauch der bei der Thermoanalyse geschaffenen Löcher ab. Das monotone Ansteigen der -Werte bei steigender Co²⁺-Konzentration stimmt mit dem Überspringen von Elektronen zwischen Fe²⁺ und Co³⁺ überein.

     

Kinetics and mechanisms of hydrolysis of tetraphenylporphyrins tethered to silicate glass via a primary or tertiary alcohol linker

Tetraphenylporphyrins carrying primary or tertiary alcohols in a phenyl group were bonded to silicate glass by heat treatment. The rate of base catalyzed hydrolysis of tertiary ester was 20 times slower than that of primary ester, while the rate of acid catalyzed hydrolysis of tertiary ester was only 2.5 times slower than that of primary ester. Hydrolysis of tertiary alcohol bonded silica in HCl/H₂¹⁸O${{\text{H}}_2}^{18}\text{O}$ displayed that there is a covalent bond between alcohol oxygen and silicon, and the C–O bond is cleaved under acidic conditions, while the Si–O bond is cleaved under basic conditions.     

A green route to 1,2-cyclohexanediol via the hydrolysis of cyclohexene oxide catalyzed by water

Effective hydrolysis of cyclohexene oxide (CHO) was conducted by heating in water between 100 and 140?°C without another catalyst. It provided 100?% purity and 100?% yield of trans-1,2-cyclohexanediol (1,2-CHD) with five times of H₂O to CHO at 120?°C for 6?h. These intermediates of polyether polyols could be totally decomposed to 1,2-CHD (monomer) by hot water under the same condition. The improved process eliminates the purification and markedly reduces the cost of 1,2-CHD in the follow-up industrial production. The main factors, such as reaction temperature, time, and water volume, were investigated. It was proposed that water acted as a modest acid catalyst, reactant, and solvent in the hydrolysis of CHO and polymers.     

Preparation and thermal decomposition study of pyridinedicarboxylate intercalated layered double hydroxides

Supramolecular 2,3- and 2,5-pyridinedicarboxylate (PDC) intercalated ZnAl-layered double hydroxides (2,3- and 2,5-PDC–ZnAl–LDHs) have been prepared by ion exchange method. The structure and composition of the intercalated materials have been studied by X-ray diffraction (XRD) and inductively coupled plasma emission spectroscopy (ICP). The study indicates that the 2,3-PDC and 2,5-PDC anions are accommodated as interdigitated bilayer and monolayer arrangement respectively between the sheets of LDHs. Furthermore, their thermal decomposition processes were studied by the use of in situ high temperature X-ray diffraction (HT-XRD), and the combined technique of thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS) under N2 atmosphere. Based on the comparison study on the temperatures of both decarboxylation and complete decomposition of interlayer PDC, it can be concluded that 2,5-PDC–ZnAl–LDHs has higher thermal stability than that of 2,3-PDC–ZnAl–LDHs.     

Synthesis and characterization of sulfate and dodecylbenzenesulfonate intercalated zinc-iron layered double hydroxides by one-step coprecipitation route

Inorganic sulfate- and organic dodecylbenzenesulfonate (DBS)-intercalated zinc-iron layered double hydroxides (LDHs) materials were prepared by one-step coprecipitation method from a mixed salt solutions containing Zn(II), Fe(II) and Fe(III) salts. The as-prepared samples have been characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), low-temperature nitrogen adsorption, scanning electron microscopy (SEM), inductively coupled plasma emission spectroscopy (ICP), and Mössbauer spectroscopy (MS). The XRD analyses demonstrate the typical LDH-like layered structural characteristics of both products. The room temperature MS results reveal the characteristics of both the Fe(II) and Fe(III) species for SO₄²⁻-containing product, while only the Fe(III) characteristic for DBS-containing one. The combination characterization results and Rietveld analysis illustrate that the SO₄²⁻-containing product possesses the Green Rust two (GR2)-like crystal structure with an approximate chemical composition of [Zn_0.435·Fe^II_0.094·Fe^III_0.470·(OH)₂]·(SO₄²⁻)_0.235·1.0H₂O, while the DBS-containing one exhibits the common LDH compound-like structure. The contact angle measurement indicates the evident hydrophobic properties of DBS-containing nanocomposite, compared with SO₄²⁻-containing product, due to the modification of the internal and external surface of LDHs by the organic hydrophobic chain of DBS.     

Stabilization of Co in layered double hydroxides (LDHs) by microwave-assisted ageing

Co-containing layered double hydroxides at different pH have been prepared, and aged following different routes. The solids prepared have been characterized by element chemical analysis, powder X-ray diffraction, thermogravimetric and differential thermal analyses (both in nitrogen and in oxygen), FT-IR and Vis-UV spectroscopies, temperature-programmed reduction and surface area assessment by nitrogen adsorption at −196 °C. The best conditions found to preserve the cobalt species in the divalent oxidation state are preparing the samples at controlled pH, and then submit them to ageing under microwave irradiation.     

Aqueous uranyl complexes. 3. Potentiometric measurements of the hydrolysis of uranyl(VI) ion at 25°C

Potentiometric titrations of uranyl(VI) solutions were conducted using a standard glasslcalomel electrode combination over the pH range 3 to 12 at 0.1 molkg^–1 ionic strength with tetramethylammonium trifluoromethanesulfonate as the supporting electrolyte. The electrodes were calibrated directly on the hydrogen ion concentration scale during the initial stage of each titration. The species, UO ₂ ²⁺ , (UO₂)₂(OH) ₂ ²⁺ , (UO₂)₃(OH) ₅ ⁺ , (UO₂)₃(OH) ₇ ^– , (UO₂)₃(OH) ₈ ^2– , and (UO₂)₃(OH) ₁₀ ^4– identified in an earlier Raman study were compatible with the analysis of the titration data. Based on this analysis and application of the extended Debye-Hückel treatment, the polynuclear species indicated above were assigned overall formation constants at 25°C and at infinite dilution of –5.51±0.04, –15.3±0.1, –27.77±0.09, –37.65±0.14, and –62.4±0.3, respectively. The results are discussed in reference to hydrolysis quotients reported in the literature for the first three species. Formation quotients for the last two species have not been reported previously.     

Nanostructured ultra-low-κ porous fluoropolymer composite films via plasma co-polymerization of hydrophobic and hydrophilic monomers and subsequent hydrolysis treatment

A new approach to fabricate porous nanostructured fluoropolymer composite films with a low dielectric constant (κ) was put forward at the first time. Initially, a film (pp-HDFD-PEGMA film) composed of dense, uniform, and well-defined nanospheres was controllably deposited on hydrogen-terminated silicon substrates by simultaneous plasma polymerization and deposition of a fluorine-containing hydrophobic monomer, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluoro-1-decene (HDFD), and a hydrophilic monomer poly(ethylene glycol) methacrylate (PEGMA), using a pulsed plasma polymerization technique. Then, by hydrolysing the plasma co-deposited film in aqueous hydrochloric acid solution to effectively remove the soluble nanospheres or fragments which mainly derived from PEGMA, a nanoporous fluorocarbon film was achieved. Subsequently, a top poly(tetrafluoroethylene) layer was deposited via the magnetron sputtering process to cap and complete an encapsulated structure. The resulting bilayer composite film consisting of a layer of nanostructured fluorocarbon porous film and a layer of encapsulation fluorocarbon polymer has a κ value of 1.8. The morphology investigation of the plasma co-deposited film prior and after acid-treatment by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) confirmed the form of the nanospheres and nanoporous structure, while the chemical composition and structure analysis by X-ray photoelectron spectroscopy (XPS) revealed that after the acid-treatment, the porous nanostructured film are composed predominantly of mainly fluorocarbon polymer.     

Thermal evolution of V(III)-containing layered double hydroxides

A study is reported on the thermal evolution of Mg, V layered double hydroxides with interlayer carbonate anions and different Mg/V molar ratios (from 1 to 4). Decomposition in O₂ occurs at lower temperature than that in N₂; the stability of the layered structure decreases as the V content increases. Oxidation of layer V³⁺ cations occurs in the same temperature range as dehydroxylation and decarbonation. The nature of the crystalline phases formed upon calcination at high temperatures strongly depends on the Mg/V molar ratio in the initial solid.     

Synthesis pretreatment and characterization of a magnetic layered double hydroxides fluorescent probe

Using magnetic layered double hydroxide （MLDH） as carrier of fluorescein （FLU）, a fluorescent composite of MLDH-FLU was prepared via intercalation reaction of ion change. The crystal properties of MLDH-FLU were investigated through XRD, IR, TEM and TG-DSC characterization. It is shown that the crystal type of MLDH-FLU composite matched well with R-hexagonal crystal system of MLDH, with crystal cell parameters of a, c and channel height h equal to 0.3199, 2.411 and 0.3267 nm respectively. The superabundant pigment adsorbed outside the composite should be cleared before interference with cells, but excessive wash would decrease stability and cause crystal phase transformation of MLDH.