Competition between Band Filling and Steric Effect in Ordered Double Perovskites Sr_(2-x)La_xMnMoO_6

The ordered double perovskites, Sr2-xLaxMnMoO6, were prepared by sol-gel reaction. Structural, magnetic, and electrical properties were investigated for a series of ordered double perovskites Sr2- x Lax MnMoO6 （0 ≤ x ≤ 1 ）. The compounds have a monoclinic structure （space group P21/n） and the cell volume expands monotonically with La doping. The Tc and the magnetic moment rise and the cusp-like transition temperature below which the magnetic frustration occurs shifts to high temperature as x increases. With La doping, electrical resistivity of Sr2-x LaxMnMoO6 decreases only at low doping levels （x ≤0.2）; while at high doping levels （0.8≤x ≤1）, electrical resistivity tends to increase greatly. The resuits suggest that the competition between band filling effect and steric effect coexists in the whole doping range, and the formation of ferrimagnetic interactions is not simply at the expense of antiferromagnetic interactions.

Steric Effects in the Cl＋CHD3（v1=1） Reaction

A recent study has revealed a full 3-dimentional reactive scattering picture of the reaction CI＋CHD3（v1=1） as the C1 atoms attack CHD3 from various directions respective to the C-H stretching bond. The reported polarization-dependent differential cross sections provide the most detailed characterization of the influences of reagent alignments on reactivity. To convey the stereo-specific information more accessible to general chemists, we show here, by proper symmetry considerations, how to retrieve from the measurements the relative integral and differential cross sections of two most common collision geometries： the end-on versus side-on attacks. The results, albeit coarse-grained, provide an appealing picture that not only reinforces our intuition about chemical reactivity, but also sheds more light on the conventional （unpolarized） attributes.

Steric Effect Modulating the Structures of Trinuclear Zinc Carboxylate Frameworks

By the reaction of different aromatic dicarboxylic acid with zinc nitrate, three metal-carboxylate frameworks, [Zn3（BDC）3（EtOH）2]（1）, [Zn3（BDC）3（py）2]·2DMF（2）, and [Zn3（NH2-BDC）3（H2O）2]·5DMF（3） which are constructed on the same linear trinuclear Zn3（RCOO）6 secondary building units, have been synthesized and characterized by X-ray diffraction analyses. Structural analyses showed that there are terephthalic acids as ligand linkers to form the hxl topological layer structures for 1 and 2. The introduction of the rigid aromatic ring pyridine in 2 as the terminal co-ligand of Zn3-SBU to instead of the flexible ethanol in 1, will form the layer-pillared supramolecular systems with 2-D crisscross channels, through its π-π stacking interactions. Owing to the steric hindrance of amino groups, 3 was assembled into a three-dimensional porous structure with pcu topology derived from the 2-amino-terephthalic acid as linkers to connect the Zn3-SBUs through a head-to-tail type.

Ligand Steric Effects on Naphthyl-α-diimine Nickel Catalyzed α-Olefin Polymerization

Naphthyl-α-diimine nickel complexes with systematically varied ligand sterics, activated by modified methylaluminoxane（MMAO）, were tested in the polymerization of higher α-olefin（1-hexene, 1-decene and 1-hexadecene） under suitable conditions. The polymerization results indicated the possibility of precise microstructure control, depending on catalyst structure, polymerization temperature, monomer concentration and types of monomers, which in turn strongly affects the resultant polymer properties. Naphthyl-α-diimine nickel complex bearing chiral bulky sec-phenethyl groups in the o-naphthyl position showed good catalytic activity, and resulted in branched polymers（42-88/1000 C） with high molecular weights（Mn：（4.3-15.2） × 10^4 g·mol^-1） and narrow molecular weight distribution（Mw/Mn = 1.13-1.29, RT）, which suggested a living polymerization. The increasing steric hindrance of catalyst leads to enhance insertion for 2,1-insertion of α-olefin and the chain-walking reaction.

Study on fluorescence properties of rare earth complexes influenced by steric effect

The rare earth complexes Tb（o-BrBA）3,Tb（m-BrBA）3 and Tb（p-BrBA）3 were synthesized using o-,m-,p-bromo benzoic acids（2-bromo benzoic acid,3-bromo benzoic acid and 4-bromo benzoic acid） as ligand,respectively.The UV spectra showed that the absorption ability of Tb（m-BrBA）3 was the strongest.However,the fluorescent intensity of Tb（o-BrBA）3 was the weakest.The effect of the molecular structure,the energy level of Tb3＋ and energy transfer efficiency from ligands to Tb3＋ were discussed to explain the experimental results.The results indicated that,due to the large atomic radius of bromine,the steric effect caused by the different substitution bromine on the benzene ring might strongly affect the bond length formed by the coordination atoms and Tb3＋.The longer the bond length was,the lower the efficiency of energy transfer was,and the weaker the fluorescent intensity was.

Single molecular insight into steric effect on C-terminal amino acids with various hydrogen bonding sites

Amino acids are basic units to construct a protein with the assistance of various interactions.During this building process,steric hindrance derived from amino acid side groups or side chains is a factor that could not be ignored.In this contribution,adsorption behaviors of C-terminal amino acid derivatives with amino acid residues fused in 3,4,9,10-perylenetetracarboxylic dianhydride were investigated by scanning tunneling microscopy(STM)and density functional theory(DFT)calculations at various liquid/solid interfaces.STM results at 1-phenyloctane/HOPG interface show that N,N'-3,4,9,10-perylenedicarboximide(GP)and N,N'-methyl-3,4,9,10-perylenedicarboximide(AP)formed linear and herringbone structures,respectively.The driving force could be attributed to different H-bonding sites induced by steric hindrance at side groups.N,N'-Benzyl-3,4,9,10-perylenedicarboximide(PP)generates both linear and herringbone structures because steric hindrance changes the H-bonding sites between PP molecules,whereas N,N'-isopropyl-3,4,9,10-perylenedicarboximide(LP)failed to be imaged because of strong steric hindrance coming from larger side group.To further investigate the impact of steric hindrance,we utilized octanoic acid(OA)as solvent to capture the adsorption details of LP and PP.We found that OA molecules drag PP and LP molecules in a different direction to generate linear structure,impeding the molecular rotation.The structure–solvent relationship shows that the steric hindrance is brought by the large side group,which makes it easier to recognize OA molecules at the interface.These results demonstrate that steric effect plays a significant role in altering interaction sites of the compounds during the adsorption process at the liquid/solid interface.

Structural tailoring of covalent organic frameworks with steric effects

Covalent organic frameworks(COFs)provide a unique platform with tunable structures allowing precise control of pore sizes,shapes and functions.The key to synthesizing COFs with desired structures is to precisely control the conformation and geometry of building blocks as well as the growth direction of COFs.To achieve this,steric effects are noteworthy that may have a significant impact on the assembly of COFs.Specifically,the introduction of sterically demanding substituents or bulky groups into monomers of COFs will lead to intramolecular conformational changes and intermolecular repulsions,which induce structural changes in COFs,including changes in torsion angles,interlayer distances,stacking modes and topologies of 2D COFs,and changes in spatial nodes,interpenetration and topologies of 3D COFs.This review will help to understand the impacts of steric effects on the structures of COFs and to take them into extensive consideration in the design and synthesis of COFs with novel functionalities and structural attributes.

THE STEPWISE EXCHANGE ACTION AND STERIC HINDRANCE EFFECT OF ORGANIC PHENOLS ON CLAYS IN SEAWATER

The exchange action of six types of organic phenols on clay surfaces in seawater is systematically studied in this work. The following significant conclusions are drawn from the experiments. (1) The interaction of organic phenols with montmorillonite, illite and kaolinite in seawater is monovalent anion exchage.(2) Their isotherms of stepwise exchage on clay surfaces belong to the Langmuir type or stepwise type.(3) The discovery of the"steric hindrance effects of stepwise exchange of organic phenols on clays surfaces", and revelation of an exchange mechanisrn diffeient from that in references are the greatest achieverments in this work.

The effect of cation–π interactions in electrolyte/organic nanofiltration systems

The rejection properties of a nanofiltration organic membrane were investigated using KCI solutions, NaC1 solutions, NaC1/benzyl alcohol hybrid solutions and KCl/benzyl alcohol hybrid solutions. The presence of benzyl alcohol （3.7 mol · m-3） caused a decrease in electrolyte rejection within the range of 0 to 6%. The mechanism of the decrease was discussed. The cation-n bond was assumed to form in the hybrid solution and to further induce the partial dehydration of the cation. The steric and charge density inhibition of the salt activity was strengthened, and the salt rejection was thus decreased. A simulation was performed to evaluate the radius of the cation. 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.

Which Information Theoretic Quantity Should We Choose for Steric Analysis of Water Nanoclusters(H2O)n(n=6,32,64)?

As evidenced from recent literature,interest in employing information theory measures for understanding different properties of atomic and molecular systems is increasing tremendously.Following our earlier efforts in this field,we here evaluate the feasibility of using information theory functionals such as Fisher information,Shannon entropy,Onicescu information energy,and Ghosh-Berkowitz-Parr entropy as measures of steric effects for the steric analysis of water nanoclusters.Taking the structural isomers of water hexamers as working models and using information theoretic quantities,we show that the relative energies of water nanoclusters and the computed steric energies are related.We also show the strong effects of steric repulsion on conformational stabilities.At the same time,we have also assessed the usefulness of simultaneously considering the different information theoretic quantities,and achieved more accurate descriptions of the stability of water nanoclusters.In order to consider the effects of cluster size on the obtained results and the extent of applicability of information theoretic quantities,we have also benchmarked larger water nanoclusters with 32 and 64 units.Scrutinizing the obtained data from information theory functionals,we found that Fisher information shows the best overall performance.Our findings underline that the information theoretic quantities,especially Fisher information,can be used as quantitative measures of relative energies and consequently the order of stability of nanoclusters,which affirmed the utility of information theory for investigating various physical and chemical problems.

辨析基础有机化学教材中的争议问题:乙烷构象稳定性的来源

烷烃的构象及其稳定性是基础有机化学中重要的知识点,其中乙烷的交叉式与重叠式构象是其中最基础的部分。现行的国内外本科基础有机化学教材中关于乙烷的交叉式构象比重叠式构象稳定的原因给出了不同的解释,比较混乱,不易于本科教学。本文调研了文献,梳理出乙烷交叉式构象稳定性来源的不同论点和论据,并指出先前文献分析与计算方法的不足。通过文献调研,我们认为超共轭效应和空间位阻效应两种因素都需要写入教材中。

创新创业“五维一体”育人模式探究

“五维一体”育人模式是指创新创业目标、课程、师资、管理、评价五个维度的一体化,其有效运行离不开五个维度内部的一体化和五个维度之间的立体联动。“五维一体”育人模式的构建需要明确育人方向、夯实课程基础、优化师资队伍、实现政企校共赢、倡导多维评价的一体化。

可逆SCSC转变中铜(Ⅱ)配合物的可视变色:结构对颜色的影响

设计了一个以单晶-单晶(SCSC)转变这种新的固相无机合成方法为核心的8学时综合化学实验。首先采用直接加成法分别合成了粉末形态与大单晶形态的绿色配合物(H_(3)O)[K(15C5)_(2)][CuCl_(4)](1),其在温度诱导下转变为红色配合物[K(15C5)_(2)][CuCl_(3)](2),这是由于在固相中[K(15C5)_(2)]^(+)的空间位阻效应限制了[CuCl_(3)]−的二聚。并且配合物2在盐酸蒸气诱导下经过SCSC转变恢复为配合物1。配合物1和2之间的SCSC转变也可以通过文字或图画颜色可逆变化的形式在滤纸上呈现,反应迅速,实验现象直观明显,有助于激发学习兴趣。进而,学生可以根据学过的本科无机化学中涉及的晶体场理论内容判断出两种配合物颜色的差异是因为铜(Ⅱ)的配位数不同而导致,有效地促进其将理论知识应用于实践中。通过单晶X射线衍射、粉末X射线衍射、紫外-可见光谱和傅里叶红外变换光谱等对产品进行表征,结果表明,配合物1和2晶型不同而且单晶转化完全,该过程锻炼了学生对剑桥晶体结构数据库的使用,有助于提升学生的数据分析能力和规范安全操作大型仪器的科学素养。本实验学时安排紧凑,可进行模块化教学,试剂成本低廉,适合在化学及相关专业的本科实验教学中推广。

纳米碳酸钙抗团聚机理及分散规律实验研究

静电位阻和空间位阻是纳米碳酸钙抗团聚的两个主要因素。根据其抗团聚机理，分析了机械剪切对纳米碳酸钙的分散作用。结果表明，单纯采用高速搅拌，转速需达到5000r／min以上才能分散纳米碳酸钙，但溶液不稳定，静置后易分层。分析了聚合醇SD-301对纳米碳酸钙的分散作用后发现，聚合醇加量为90kg／m^3时，纳米碳酸钙粒子平均值最小（35．7nm），分布范围为20～50nm，空间位阻是其主要作用机理；生物聚合物XC加量为6kg／m^3时，纳米碳酸钙分散平均粒径为24．1nm，分布范围为15～35nm，其分散溶液为白色黏稠乳状液，稳定性好，静置时不分层。降低表面张力和空间位阻是保持纳米碳酸钙分散体系稳定的主要机理。对有机分散剂、无机分散剂与XC共同作用对纳米碳酸钙影响的分析结果表明：复合分散剂能使高分子类、无机和有机类分散剂优势互补，在降低颗粒之间范德华引力的同时，也降低了介质水的表面张力，这两方面共同作用使颗粒的润湿分散效果更佳。

钌多吡啶配合物的合成及插入配体的位阻效应对键合DNA的影响

合成了２，３－二甲基－１，４，８，９－四氮三联苯（ｄｍ ｔａｔｐ）和２，３－二苯基－１，４，８，９－四氮三联苯（ｄｐｔａｔｐ）两种新配体及它们与 ２，２′－联吡啶和钌（Ⅱ）的混配物［Ｒｕ（ｂｐｙ）２ｄｍ ｔａｔｐ］２＋ （１）和［Ｒｕ（ｂｐｙ）２ｄｐｔａｔｐ］２＋ （２）， 用电子吸收光谱、稳态荧光、粘度测定和圆二色谱研究了配合物与小牛胸腺ＤＮＡ的相互作用． 结合我们以前对配合物［Ｒｕ（ｂｐｙ）２ｔａｔｐ］２＋ （３） （ｔａｔｐ 为１，４，８，９－四氮三联苯）与小牛胸腺ＤＮＡ的作用研究， 得出配合物与ＤＮＡ的键合强度顺序为： ［Ｒｕ（ｂｐｙ）２ｔａｔｐ］２＋ ＞［Ｒｕ（ｂｐｙ）２ｄｐｔａｔｐ］２＋ ＞ ［Ｒｕ（ｂｐｙ）２ｄｍ ｔａｔｐ］２＋ ， 这与插入配体的位阻效应的减少趋势相一致． 同时，还测定了配合物与ＤＮＡ的键合常数．

农药西维因及敌草隆在草木灰上的吸附行为研究

测定分析了草木灰的孔隙结构、表面性质及化学组成,选择理化参数接近,空间构型不同的2种农药西维因和敌草隆作为吸附质,研究其在草木灰上吸附行为,结果表明两者在草木灰上吸附模式理截然不同,线性吸附方程及准一级动力学方程能够拟合平面型分子西维因的吸附等温线及动力学曲线,Freundlich吸附等温式及二级动力学方程吸附对非平面型分子敌草隆的等温线及动力学曲线拟合程度最高,说明平面型分子的吸附可能以简单的线性分配为主,而非平面型分子可能以多过程非线性吸附为主;等温线及动力学拟合参数显示,草木灰对平面型分子西维因的吸附量远大于非平面型分子敌草隆,说明吸附质分子的空间位阻效应是影响吸附的重要因素.

十二叔胺系列捕收剂对石英的浮选性能研究

研究了4种十二取代叔胺(DRN、DEN、DPN和DBN)对石英的浮选行为,结果显示4种叔胺中DRN、DEN和DPN对石英的浮选性能都较好,浮选回收率均能达到90%以上,DBN的回收率较低。红外光谱和表面动电位研究结果表明,石英的表面主要带负电,矿物表面的羟基电离是其表面荷电的主要原因。4种叔胺与石英表面的作用机制主要是静电作用。与叔胺作用后,石英的动电位值显著增加。氮原子上连接的取代基的电子效应和空间效应导致了DRN、DEN、DPN和DBN的浮选能力存在差异。

长程范德华力导向作用下胶体凝聚的计算机模拟

采用计算机模拟方法研究了长程范德华力在胶体凝聚过程中的作用,发现由于胶粒间的范德华力是长程力,它对胶粒或团簇运动将产生导向作用.与不考虑导向作用的扩散控制团簇凝聚(DLCA)模型比较,这种导向作用不仅加速了胶体的凝聚过程,而且形成了更致密、分形维数更大的结构体.研究还发现,长程范德华力导向作用对胶粒的初始浓度非常敏感,不论是在凝聚物的结构还是凝聚速率方面,只有在胶粒初始浓度较低时,该导向作用效应才明显.其可能的原因是,在胶粒初始浓度较高时,由于胶粒布朗运动的平均自由程很短而且位阻效应大,从而使导向作用效应未能反映出来.

一锅法有效合成氨基甲酸酯类化合物

以四甲基胍(TMG)为催化剂,乙腈(ACT)为溶剂,利用CO_2、胺和烷基氯三组分在0.10MPa,70～80℃条件下,一锅法有效合成氨基甲酸酯类化合物,并研究了收率和产率的影响.结果表明,最优反应条件为n(胺)∶n(烷基氯)=3～4、反应温度70～80℃、反应时间2～3h、酯分离收率达68.7%～81.3%,酯纯度达到99.9%.

甲壳型液晶高分子的化学结构及其与性能间关系的研究

设计并合成了７种新型甲壳型液晶高分子，研究了液晶基元的化学结构和立体效应对单体及其聚合物液晶性的影响．发现在液晶基元的末端引入极性或可极化的原子基团提高了单体的熔点和液晶相的热稳定性；液晶基元的长径比越大，单体的熔点和清亮点越高；聚合使单体的液晶稳定性增加、液晶相温度范围变宽；侧链液晶基元的极性、刚性和空阻越大，聚合物的玻璃化温度越高；酰胺基团无论是在分子的末端还是在连接部位，都使单体的熔点和聚合物的玻璃化温度提高，但在分子末端时液晶相较稳定，作为中心桥键时不利于液晶相的稳定形成．