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.     

九年级学生三重表征转换能力的发展过程:基于眼动的证据*

九年级学生在化学学习的过程中开始建立三重表征思维,同时,不同学业水平学生的三重表征转换能力会出现分化。为了探究学生在各个阶段三重表征转换能力的发展特点,采用眼动分析法对12名九年级学生进行了一学期的追踪实验。研究发现:(1)入门时期,学生进行不同表征之间转换的能力是有差异的,并且表现出转换和逆向转换能力的不对称性特点。学优生与学中生、学困生的三重表征转换能力有明显差异,但学中生与学困生的三重表征转换能力还没有表现出明显差异。(2)突破时期,学生进行宏观(中心)、符号(中心)、微观(中心)转换的注视点个数、测试总时间没有表现出统计学差异。学优生与学中生的转换能力分化更明显,学中生与学困生开始出现差异。(3)深化时期,学生宏观(中心)表征能力最强,符号(中心)表征能力次之,微观(中心)表征能力最弱。学优生与学中生、学困生的转换能力差异显著,学中生的间接转换频率明显增加。     

二维三温能量方程的九点差分格式及其迭代解法

给出了激光驱动内爆数值模拟中二维三温能量方程的九点差分格式及其迭代解法,并给出了九点差分格式与五点差分格式对比计算结果,对一维和二维物理模型进行了数值模拟,得到了令人满意的数值结果。     

CCD细分技术方法研究及应用

依据线阵CCD和面阵CCD细分技术的原理，提出了九点四线曲面拟合的面阵CCD细分方法，并通过与均值法对比以及在图像放大和图像定位中的实际应用，证明了该方法不仅计算简便、图像相关度高、边缘趋势保持较好，而且可大大提高图像的分辨率和目标图像的定位精度。     

Polyhedral structures with an odd number of vertices: nine-coordinate metal compounds

The stereochemistry of nine-coordinate transition-metal and rare-earth compounds has been studied by means of continuous shape measures (CShM) and related tools. Several reference nine-vertex polyhedra have been defined and their minimal distortion interconversion paths established. A theoretical shape map is presented in which the structures can be placed according to their distances in CShM space to the capped square antiprism and the tricapped trigonal prism, which are the most common polyhedra in nine-coordinate compounds. The structures of almost 2000 metal coordination spheres in molecular and extended solid-state compounds have been analyzed. Clear stereochemical trends can be established for subsets of these compounds grouped according to the nature of their ligands, which include families of compounds spread along the interconversion paths between the capped square antiprism and the capped cube, or between the tricapped trigonal prism and the tridiminished icosahedron.     

九年级化学教材中化学史内容分析与编写建议

通过对4个版本九年级化学教材中化学史内容选取与编排情况的统计和分析,发现随着新课程改革的不断深入,教材中化学史案例数量明显增多,其教育价值已经被广泛认可。虽然教材中关于化学史的内容编排图文并茂,但改进空间依然存在,例如化学家介绍过于简略,介绍角度不够全面;化学发展的描述局限于个别科学家的贡献和孤立的科学事件;化学史学习形式单一、地位不高。为更好地发挥化学史蕴含的教育功能,建议教材中化学家的形象更加丰满,化学研究过程更加完整真实,设计丰富的化学史学习活动,以使学生更加重视化学史的学习,从中受益。     

Factors contributing to one-electron metalloradical activation of ethene and carbon monoxide illustrated by reactions of Co(II), Rh(II), and Ir(II) porphyrins

Metallo-porphyrin complexes of Co(II), Rh(II), and Ir(II) are used as prototype metal-centered radicals in examining the factors that contribute to obtaining one-electron activated ethene and CO substrate adducts [M(CH₂CH₂)] and [M(CO)] that subsequently react on to produce complexes with reduced substrate units including M-CH₂CH₂-M, M-(CH₂)₄-M, M-C(O)-M, M-C(O)-C(O)-M, and M-C(O)H. Cobalt(II) and rhodium(II) complexes of the form [(por)M(CH₂CH₂)] and [(por)M(CO)] occur as primarily metal-centered radicals and the iridium analogs are porphyrin anion radical complexes ((por)⁻Ir^III(CH₂CH₂), (por)⁻Ir^III(CO)). Relatively small (por)Co-C bond dissociation enthalpies preclude forming any reduced substrate species. Rhodium porphyrins produce a complete set of reduced and coupled ethene and CO complexes, but iridium porphyrins only give ethene reduction and coupling products (por)Ir-CH₂CH₂-Ir(por) and (por)Ir-(CH₂)₄-Ir(por). Thermodynamic criteria and analysis of substrate reactions are used to guide interpretations of the observed reactivity.     

非正交网格上的九点格式在热传导问题中的改进

对文献[1]在二维Lagrange流体力学网格上构造的扩散方程九点差分格式做了进一步的讨论和改进,给出了一般形式边界条件的计算格式。数值试验的结果表明,这些改进提高了原格式数值结果的精度。