Octacyanidorhenate(V) Ion as an Efficient Linker for Hysteretic Two-Step Iron(II) Spin Crossover Switchable by Temperature,Light, and Pressure

A two-step hysteretic Fe^II spin crossover (SCO) effect was achieved in programmed layered Cs{[Fe(3-CNpy)₂][Re(CN)₈]}⋅H₂O ( 1 ) (3-CNpy=3-cyanopyridine) assembly consisting of cyanido-bridged Fe^II-Re^V square grid sheets bonded by Cs⁺ ions. The presence of two non-equivalent Fe^II sites and the conjunction of 2D bimetallic coordination network with non-covalent interlayer interactions involving Cs⁺, [Re^V(CN)₈]³⁻ ions, and 3-CNpy ligands, leads to the occurrence of two steps of thermal SCO with strong cooperativity giving a double thermal hysteresis loop. The resulting spin-transition phenomenon could be tuned by an external pressure giving the room-temperature range of SCO, as well as by visible-light irradiation, inducing an efficient recovery of the high-spin Fe^II state at low temperatures. We prove that octacyanidorhenate(V) ion is an outstanding metalloligand for induction of a cooperative multistep, multiswitchable Fe^II SCO effect.     

Organocatalytic Control over a Fuel-Driven Transient-Esterification Network**

Signal transduction in living systems is the conversion of information into a chemical change, and is the principal process by which cells communicate. In nature, these functions are encoded in non-equilibrium (bio)chemical reaction networks (CRNs) controlled by enzymes. However, man-made catalytically controlled networks are rare. We incorporated catalysis into an artificial fuel-driven out-of-equilibrium CRN, where the forward (ester formation) and backward (ester hydrolysis) reactions are controlled by varying the ratio of two organocatalysts: pyridine and imidazole. This catalytic regulation enables full control over ester yield and lifetime. This fuel-driven strategy was expanded to a responsive polymer system, where transient polymer conformation and aggregation are controlled through fuel and catalyst levels. Altogether, we show that organocatalysis can be used to control a man-made fuel-driven system and induce a change in a macromolecular superstructure, as in natural non-equilibrium systems.     

Multiscale characterization and constitutive parameters identification of polyamide (PA12) processed via selective laser sintering

This study is focused on multiscale characterization and constitutive parameters identification of selectively laser sintered PA12 specimens. The process parameters and change in crystallinity due to 3D printing were identified via differential scanning calorimetry (DSC). Tension, compression, shear, flexural and fracture tests performed on samples fabricated, both in 0° and 90° directions reveal that the tensile toughness of samples printed in 0° orientation, outperform samples printed in 90° orientation by an average of 24%. Cryogenically fractured samples were analyzed via SEM and micro-computed tomography to analyze 2D/3D defects and correlate the microstructure with macroscopic properties. The constitutive parameters for a strain-rate and temperature-dependent Three Network (TN) material model were identified using the measured mechanical properties. Furthermore, mechanical response of micro-architected Kelvin lattice structure was analyzed by Finite Element Method employing the TN constitutive model and the predictions were corroborated with measurements.     

The effect of short glass fibers on the process behavior of polyamide 12 during selective laser beam melting

In additive manufacturing, polymer composites are used for setting tailored properties. Short glass fibers can be used as fillers for polyamide 12 for enhancing stiffness or tensile strength as well as for reducing shrinkage. In this paper, the effects of short glass fibers on polyamide 12 concerning powder properties, process behavior and part properties in laser beam melting of polymers (SLS) are investigated. It could be shown that by increasing the short glass fiber content powder properties as well as part properties are immensely affected. By adding glass fibers, powder properties, like flowability and diffuse reflection decrease. The isothermal crystallization changes resulting in a narrower processing window. Concerning mechanical properties, short glass fibers allow for a higher stiffness until a critical limit of filler concentration within this study is reached, after which the tensile strength decreases. The elongation of break decreases by rising the filler content.     

Hammett and Brown correlations in the structure and electronic properties of H2Si=SiHAr (Ar = p-C6H4X; X = NH2, OH,Me, H,F, Cl,CHO, COOH,CN, NO2) molecules

Substituent effect on the structure and electronic properties of H₂Si=SiHAr (Ar = p-C₆H₄X; X = NH₂, OH, Me, H, F, Cl, CHO, COOH, CN, NO₂) molecules are studied at the CAM-B3LYP/6-311G(d,p) level of theory. Energy decomposition analysis (EDA) is used as a useful tool for illustrating the interaction between H₂Si and SiHAr fragments in HArSi=SiH₂ molecules. Energetic analysis reveals that the singlet state of the fragments is more stable than triplet state. Also, interactions are stronger in the presence of electron-withdrawing groups (EWGs) in comparison to electron donating groups (EDGs). EDG and EDG effects are investigated on the stability of fragments, frontier orbital energy, distortion, HOMO–LUMO gap, electron-donating (ω⁻) and electron-accepting (ω⁺) powers of the studied molecules. Then, the correlations between these calculated parameters with the Hammett and Brown constants (σ_p and σ_p⁺, respectively) are provided. Also, time-dependent density functional theory method (TD-DFT) is employed for the determination of the strongest absorption band values (λ_max,el) of these molecules. This absorption band is attributed to the HOMO →LUMO transition.     

Preparation and Characterization of Protonated Fumaric Acid

Fumaric acid was reacted with the binary superacidic systems HF/SbF₅ and HF/AsF₅. The O,O'-diprotonated [C₄H₆O₄]²⁺([MF₆]^–)₂ (M = As, Sb) and the O-monoprotonated [C₄H₅O₄]⁺[MF₆]^– (M = As, Sb) species are formed depending on the stoichiometric ratio of the Lewis acid to fumaric acid. The colorless salts were characterized by low-temperature vibrational spectroscopy. In case of the hexafluoridoantimonates single-crystal X-ray structure analyses were carried out. The [C₄H₆O₄]²⁺([SbF₆]^–)₂ crystallizes in the monoclinic space group C2/c with four formula units per unit cell and [C₄H₅O₄]⁺[SbF₆]^– crystallizes in the triclinic space group P1 with one formula unit per unit cell. The protonation of fumaric acid does not cause a notable change of the C=C bond length. The experimental data are discussed together with quantum chemical calculations of the cations [C₄H₆O₄ · 4 HF]²⁺ and [C₄H₆O₄ · 2 H₂CO · 2 HF]²⁺.     

Magnetoelectronic properties of ferromagnetic compounds Rb2TaZ6 (Z = Cl,Br) for possible spintronic applications

Highly spin-polarized ferromagnetic materials are essential for efficient spintronic devices. Here, 100% spin-polarized compounds Rb₂TaZ₆ (Z = Cl, Br) studied via density functional theory are reported. These compounds show stability in the ferromagnetic phase with cubic symmetry and half metallic behavior, thereby exhibiting a nonzero direct band gap in the spin-down channel and zero band gap in the spin-up configuration. The Ta-d sates contribute mainly to the net magnetic moments as explained by the crystal field theory and density of states. High Curie temperatures of 960.35 and 1021.74 K for Ra₂TaCl₆ and Rb₂TaBr₆, along with maximum spin polarizability, make these compounds favorable for efficient spintronic applications.     

常见客体分子对笼型水合物晶格常数的影响

Natural gas hydrates are considered as ideal alternative energy resources for the future, and the relevant basic and applied research has become more attractive in recent years. The influence of guest molecules on the hydrate crystal lattice parameters is of great significances to the understanding of hydrate structural characteristics, hydrate formation/decomposition mechanisms, and phase stability behaviors. In this study, we test a series of artificial hydrate samples containing different guest molecules (e.g. methane, ethane, propane, iso-butane, carbon dioxide, tetrahydrofuran, methane + 2, 2-dimethylbutane, and methane + methyl cyclohexane) by a low-temperature powder X-ray diffraction (PXRD). Results show that PXRD effectively elucidates structural characteristics of the natural gas hydrate samples, including crystal lattice parameters and structure types. The relationships between guest molecule sizes and crystal lattice parameters reveal that different guest molecules have different controlling behaviors on the hydrate types and crystal lattice constants. First, a positive correlation between the lattice constants and the van der Waals diameters of homologous hydrocarbon gases was observed in the single-guest-component hydrates. Small hydrocarbon homologous gases, such as methane and ethane, tended to form sI hydrates, whereas relatively larger molecules, such as propane and iso-butane, generated sⅡ hydrates. The hydrate crystal lattice constants increased with increasing guest molecule size. The types of hydrates composed of oxygen-containing guest molecules (such as CO₂ and THF) were also controlled by the van der Waals diameters. However, no positive correlation between the lattice constants and the van der Waals diameters of guest molecules in hydrocarbon hydrates was observed for CO₂ hydrate and THF hydrate, probably due to the special interactions between the guest oxygen atoms and hydrate "cages". Furthermore, the influences of the macromolecules and auxiliary small molecules on the lengths of the different crystal axes of the sH hydrates showed inverse trends. Compared to the methane + 2, 2-dimethylbutane hydrate sample, the length of the a-axis direction of the methane + methyl cyclohexane hydrate sample was slightly smaller, whereas the length of the c-axis direction was slightly longer. The crystal a-axis length of the sH hydrate sample formed with nitrogen molecules was slightly longer, whereas the c-axis was shorter than that of the methane + 2, 2-dimethylbutane hydrate sample at the same temperature.     

基于FeWOx/SiO2载氧体的甲烷化学链部分氧化反应

甲烷具有价格低廉且储量丰富的优点,因此将甲烷转化为合成气(一种H2:CO为2的混合物),从而进一步合成有价值的化学品和液体燃料引起了人们的极大关注.化学链甲烷部分氧化(CLPOM)技术能避免甲烷与空气直接接触而引起爆炸的危险,可以降低后续对合成气与氮气分离操作所带来的费用,因此日益受到关注.CLOPM过程主要分为两步:第一步,CH4被载氧体所携带的氧部分氧化,载氧体被还原;第二步,利用氧化剂(例如空气)将被还原的载氧体再氧化恢复.因此,载氧体在CLOPM过程中起到至关重要的作用.载氧体的选择主要存在两个问题:(1)甲烷被活化所产生含碳产物的能力与晶格氧的给氧能力不匹配所带来的严重碳沉积;(2)金属离子间扩散速率不匹配而造成载氧体在氧化还原过程中结构的不可逆变化.基于上述两个问题,本文设计了FeWOx/SiO2载氧体用于CLPOM.与未改性的WO3/SiO2载氧体相比,甲烷的转化率和合成气的收率都有显著提高.FeWOx/SiO2在900℃、1 atm反应条件下表现出62%的甲烷转化率、93%的CO气相选择性、94%的H2选择性和2.4的H2/CO比值,同时在50个循环中表现出优异的催化活性和稳定性.本工作利用CH4脉冲反应研究了FeWOx/SiO2的甲烷表面反应过程;采用CH4-TPR和H2-TPR相结合探究了甲烷活化速率与晶格氧扩散速率之间的关系;通过XPS和XRD对FeWOx/SiO2在氧化还原过程中的结构稳定性进行了探讨.综合上述实验结果,对FeWOx/SiO2应用于CLPOM的反应机理进行了阐述.H2-TPR结果表明,在FeWOx/SiO2中,相较于Fe2O3/SiO2,Fe-O的活性受到抑制,使其更倾向于与甲烷发生部分氧化反应;相较于WO3/SiO2,W-O的活性得到明显提升,因此更多的晶格氧可以参与到部分氧化反应中来氧化积碳,从而使合成气收率大幅度提升.从CH4-TPR结果可以看出,对于FeWOx/SiO2,CO与H2的生成温度最接近,意味着晶格氧的传输速率较快并且能够与甲烷活化产生含碳中间物种的速率相匹配,将其及时氧化生成CO,避免由于积碳造成的催化剂失活.结合XPS和XRD结果可以得出,在甲烷还原过程中,FeWOx经历一步还原形成Fe-W合金,由于其间存在强相互作用,因而抑制了还原过程中催化剂相分离现象的发生.同时,根据铁钨离子在空气条件下扩散速率的公式计算可以得出,其相近的离子氧化速率也保证了在氧化过程中催化剂结构的稳定性.本工作为进一步构建用于甲烷化学链部分氧化制合成气的复合金属氧化物载氧体提供了研究思路.