Breathing Effect in a Cobalt Phosphonate upon Dehydration/Rehydration: A Single‐Crystal‐to‐Single‐Crystal Study

Two cobalt phosphonates, [Co₂(2,2′‐bpy)₂(H₂O)(pbtcH)] ( 1 ) and [Co₂(H₂O)(pbtcH)(phen)₂] ( 2 ; pbtcH₅=5‐phosphonatophenyl‐1,2,4‐tricarboxylic acid, 2,2′‐bpy=2,2′‐bipyridine, phen=1,10‐phenanthroline), with layer structures are reported. Compound 1 contains O‐C‐O and O‐P‐O bridged tetramers of Co₄, which are further connected by pbtcH^4? units to form a layer. In compound 2 , the cobalt tetramers made up of water‐bridged Co₂ dimers and O‐P‐O linkages are connected into a layer by pbtcH^4? units. Upon dehydration, compounds 1 and 2 experience single‐crystal‐to‐single‐crystal (SC–SC) structural transformations to form [Co₂(2,2′‐bpy)₂(pbtcH)] ( 1 a ) and [Co₂(pbtcH)(phen)₂] ( 2 a ), respectively. The process is reversible in each case. Notably, a breathing effect is observed for 1 , accompanied by pore opening and closing due to the reorientation of the coordinated 2,2′‐bpy molecules. The transformation was also monitored by in situ IR measurements. Magnetic studies reveal that antiferromagnetic interactions are mediated between the magnetic centers in compounds 1 and 1 a , whereas ferromagnetic interactions are dominant in compound 2 .     

Distinct Stepwise Reduction of a Nickel?Nickel‐Bonded Compound Containing an α‐Diimine Ligand: From Perpendicular to Coaxial Structures

A nickel? nickel‐bonded complex, [{Ni(μ‐L^.?)}₂] ( 1 ; L=[(2,6‐iPr₂C₆H₃)NC(Me)]₂), was synthesized from reduction of the LNiBr₂ precursor by sodium metal. Further controllable reduction of 1 with 1.0, 2.0 and 3.0 equiv of Na, respectively, afforded the singly, doubly, and triply reduced compounds [Na(DME)₃] ? [{Ni(μ‐L^.?)}₂] ( 2 ; DME=1,2‐dimethoxyethane), [Na(Et₂O)]Na[(L^.?)Ni? NiL^2?] ( 3 ), and [Na(Et₂O)]₂Na[L^2?Ni? NiL^2?] ( 4 ). Here L represents the neutral ligand, L^.? denotes its radical monoanion, and L^2? is the dianion. All of the four compounds feature a short Ni? Ni bond from 2.2957(6) to 2.4649(8) Å. Interestingly, they display two different structures: the perpendicular ( 1 and 2 ) and the coaxial ( 3 and 4 ) structure, in which the metal? metal bond axis is perpendicular to or collinear with the axes of the α‐diimine ligands, respectively. The electronic structures, Ni? Ni bonding nature, and energetic comparisons of the two structure types were investigated by DFT computations.     

Microstructure, distribution and properties of conductive polypyrrole/cellulose fiber composites

Highly intrinsic conductive polypyrrole/cellulose fiber composites (CF) were successfully prepared through in situ chemical oxidation polymerization simply by increasing fiber concentration at the same dosage of pyrrole, oxidant and dopant (based on the weight of dry fiber). FeCl₃ and anthraquinone-2-sulfonic acid sodium salt (AQSNa) were utilized as oxidant and dopant. As fiber concentration increased from 1 % (CF1) to 20 % (CF20), N and S content increased from 0.24 and 0.25 % to 1.24 and 0.89 %, and great increase in the retention of PPy and AQSNa was confirmed by elemental analysis. In addition, on the surface of conductive fiber, PPy of compact fibroid structure was detected instead of interconnected globular structure at higher fiber concentration. Furthermore, scanning transmission electron microscope and X-ray photoelectron spectroscopy (XPS)-depth profile analysis demonstrated denser and more uniformly distributed PPy inside fiber wall for CF20, while PPy tended to deposit on the surface of fiber for CF1. Fourier transform infrared spectroscopy, together with XPS certified that the PPy with longer conjugation length and higher doping level across the conductive fiber was obtained at higher fiber concentration. The doping level for CF10 decreased from 21.55 to 16.39 % with increasing fiber wall thickness, while that of CF20 decreased slightly from 30.73 to 24.10 %. The resulting CF20 showed lowest surface resistivity of 0.433 KΩ/square, as well as improved electro-conductivity stability. The incorporation of more PPy in CF improved the thermal stability.     

Al2O3-SiO2催化环己胺氧化制备环己酮肟

以Al2O3-SiO2为催化剂,用双氧水氧化环己胺制备了环己酮肟。考察了溶剂用量、催化剂用量、反应时间和反应温度等因素对催化性能的影响。结果表明,在溶剂乙腈与环己胺体积比为3∶1,催化剂质量分数31.0%,75℃反应5 h后的环己胺转化率为100%,环己酮肟选择性可达83.6%。并对环己胺催化氧化的反应机理作了初步的探讨。     

膦手性丙炔胺脯氨酸磷酸酯螺旋聚合物的合成与表征

通过添加对映体拆分剂,合成了4种含膦手性的丙炔胺磷酸酯单体[HC帒CC H2NH(PO)R1R2].单体1,R1=OPh,R2=NC4H7COOCH3;单体2,R1=OPh,R2=NC4H7COOCH2CH3;单体3,R1=OPh,R2=NC4H7-COOC(CH3)3;单体4,R1=Ph,R2=NC4H7COOC(CH3)3].1H-NMR和31P-NMR表征可知对映体(单体1)不能被拆分剂拆分,而单体2、单体3、单体4通过拆分剂可以制得单一手性的磷化合物.以(nbd)Rh+[η6-C6H5B--(C6H5)3]为催化剂,以三氯甲烷为溶剂成功得到聚合物分子量范围在0.4×10-4～0.7×10-4,分子量分布在1.26～1.98范围的3种含手性膦侧基的丙炔胺类聚合物.比旋光度([α]D)、圆二色谱(CD)对聚合物的不同侧基及温度对光学活性的影响表明,聚合物具有良好的光学活性且能够形成单一方向的螺旋构象,说明膦手性在构建螺旋聚合物具有重要作用.     

悬浮聚合制备大尺寸梭形聚苯乙烯粒子新方法及机理研究

利用氢氧化钾对苯乙烯-马来酸酐交替共聚物(SMA)进行水解,所得中等皂化程度的SMA水解产物(SMAA)在水溶液中具有刚性棒状直链构型;将此特殊结构的大分子作为分散剂用于苯乙烯悬浮聚合,通过控制搅拌速度和油水比,可得到梭形聚苯乙烯粒子;在优化条件下,粒子平均长度6.8 mm,宽度1.4 mm,厚度0.5 mm,长径比约5.0.其可能的机理为,中等皂化程度的刚棒直链型SMAA在聚合物"软粒子"表面能形成难以"回复"的有效保护层,使由剪切形成的变形聚合物"软粒子"在聚合过程中能保持形状和尺寸的稳定,从而得到梭形聚合物粒子.     

聚合物单晶生长的三维相场模拟研究

利用元胞自动机方法与相场模型的结合建立新型三维模拟相场模型.同时,为模拟真实的、三维的高分子结晶的过程,采用元胞自动机方法离散方程,且元胞几何形状的选取符合真实聚合物晶格扩散方式的物理规律,以及新建立的相场模型套用间规聚丙烯的实验参数.利用该模型模拟了多种三维立方体或者薄层的晶体形貌及其相互之间的演化过程,包括正方形、长方形、菱形、六边形、多层单晶等.通过模拟结果与真实形貌作对比来证明所建立的相场模型真实可靠性.     

近紫外LED激发荧光粉Ba0.11Sr2.89-2xCexNaxAlO4F发光特性

采用高温固相法反应制备Ba0.11Sr2.89-2x Ce x Na x AlO4F(x=0.01,0.02,0.05,0.07,0.10,0.15)荧光粉。Ba0.11Sr2.89AlO4F体系中存在Sr(1)2+和Sr2+(2)两个格位。Sr2+(1)离子位于Wyck.4a格位,为十配位多面体构型。Sr2+(2)离子位于Wyck.8h格位,为八配位的多面体构型。研究了Ba0.11Sr2.89-2x Ce x Na x AlO4F荧光粉的紫外-可见激发、发射光谱、荧光寿命及能量传递过程,讨论并指认了Ce3+在上述两个格位中的激发带位置及能级重心,发射光谱曲线分别由两个~463,~505和~550 nm宽带发射构成。随着Ce3+浓度增加,长波发射~550 nm逐渐增强,而色品坐标(x=0.199,y=0.351)蓝绿区逐渐变化到黄绿区域(x=0.389,y=0.489)。     

具有高散射能力的聚碳酸酯复合材料的制备与性能研究

以双酚A型聚碳酸酯(PC)为基体、苯乙烯-丙烯腈共聚物(SAN)为散射体,通过熔融共混方法制备了同时具备高透光率和高雾度的高散射聚碳酸酯光散射片,研究了SAN含量对光散射片微观结构和光散射性能的影响,发现透光率和雾度同时随着散射体含量增加而提高的现象.研究结果表明,当SAN含量低于30%时,分散相为球形颗粒,颗粒的平均粒径随着SAN含量的增加而增加,而颗粒的数量浓度则随之减小,这使得其透光率和雾度均随着SAN含量的增加而增加,当SAN含量为30%时,透光率和雾度达到最大值,分别为89.1%和91.7%.并结合Mie散射理论解释说明了透光率和雾度同时随着散射体含量的增加而提高的现象.但当SAN含量的进一步增加,分散相颗粒尺寸已远大于光波的波长,不再适用于Mie散射理论,且部分不再呈球形颗粒,使得PC片的透光率和雾度略有降低.     

Elliptic and parabolic equations with measurable coefficients in weighted Sobolev spaces

We consider both divergence and non-divergence parabolic equations on a half space in weighted Sobolev spaces. All the leading coefficients are assumed to be only measurable in the time and one spatial variable except one coefficient, which is assumed to be only measurable either in the time or the spatial variable. As functions of the other variables the coefficients have small bounded mean oscillation (BMO) semi-norms. The lower-order coefficients are allowed to blow up near the boundary with a certain optimal growth condition. As a corollary, we also obtain the corresponding results for elliptic equations.