碳和硅结构化学的比较

碳和硅是元素周期表第14族的前两个元素,它们在化学中占有极其重要的地位。碳统治着有机化学,有机化合物的定义是一切含有C—C键的化合物。硅统治着无机化学,硅在地壳中的含量按40km厚度的地壳计,约占地壳质量的28%,在地壳的所有元素中,硅仅次于氧而居第二位。硅和氧以及其他元素一起结合形成硅酸盐,硅酸盐化合物占地壳质量的80%以上,单是长石一类硅酸盐矿物就占地壳质量的一半。为什么这两个元素有如此独特的能力?关键在于这两个元素的原子能各自形成独特的化学键。1碳和硅化学键的比较在基态时,碳和硅的电子组态分别为:C:[He]2s22p2;Si:…     

“物质结构与性质”中疑难问题突破举隅

以高中化学"物质结构与性质"模块教学内容为例,从分析教材文本和学生学习效果中确定教学问题,通过挖掘文本关键词、创新教学手段、查阅与研究文献对所确立的教学问题进行分析,为突破"物质结构与性质"模块的疑难问题提供参考。     

量子力学和分子力学联用方法

Till now, theoretical research has focused on some chemical behaviors, structural properties of bio-macromolecules in solutions. When the molecular force field was used to treat solution systems, not considering the movement of electrons, in many force fields the chemical bonds between atoms must be confirmed to make sure that they can’t be destroyed or formed in modeling procedure. Using quantum chemical calculation based on B-O approximation to treat solution systems, because it can consume much more resources, this method can’t treat large systems, which restricts the application of quantum chemical calculations. Moreover the hybrid QM/MM method has been widely used in research of chemical reaction in condense phase and biologic macromolecules especially the mechanisms of enzyme catalysis reactions, which has developed rapidly and takes advantage of the accuracy of QM method and high efficiency of MM method. This article will describe a brief introduction of the principle and development history of QM/MM method and give some application introductions.     

态叠加原理及其在化学中的应用

从电子的双缝干涉实验引入态叠加原理，介绍历史上对态叠加原理的争议，并分析氢原子的实波函数解与复波函数解的关系、原子光谱项、轨道杂化、价键理论等几个在结构化学中遇到的态叠加问题。     

探秘可燃冰结构的项目教学——分析、解释、预测分子的空间结构

本课程以“探秘可燃冰的结构”为项目主题,以“可燃冰”作为研究对象,在“结构决定性质”的学科观念下,开展“利用多种理论模型分析、解释、预测分子的空间结构”的项目式教学。通过“寻找甲烷分子呈现正四面体结构的证据、解释水分子的V形结构、探秘水分子如何构成冰笼子”等3个核心活动,建构利用杂化轨道理论模型、氢键模型解释分子结构和利用价层电子对互斥理论模型预测分子结构的思维路径,在解决实际问题过程中体会物质结构的复杂性。     

如何准确把握课标和教材的内容——以氧气成键特征的探讨为例

就如何准确把握课标和教材的内容,结合氧气结构的教学案例探讨了价键法不能解释氧气具有顺磁性的特性,认为氧气的分子结构应该用分子轨道理论描述,中学教学不宜要求学生用电子配对法写出氧气的电子式和结构式;提出教学要加强本体性知识和发展性知识的研修,准确把握新课标要求正确使用课程资源的建议。     

(BN)_n团簇的结构和稳定性

用HF方法、密度泛函理论的B3LYP以及微扰理论的MP2方法 ,在 6 3 1G(d)基组水平上 ,对 (BN) n(n =1～ 16)团簇的各种可能结构进行了优化 .讨论了环状与笼状稳定团簇的几何构型、自然键轨道 (NBO)、振动频率、结合能、核独立化学位移 (NICS)和能量二次差分 ,得到了 (BN) n(n =1～ 16)团簇结构的稳定性信息 .比较了HF ,B3LYP以及MP2三种理论方法对(BN) n 团簇的适应性所表现出的差异 .     

TinO2和TinO2-(n=1-10)团簇的几何结构、电子和磁性质

基于密度泛函理论(DFT)的B3LYP方法,研究了TinO2和TinO2-(n=1-10)团簇的几何结构、电子结构以及磁性.结果表明,两个氧以分离的原子状态吸附在金属团簇的表面,呈现出以一个钛原子为中心的O-Ti-O的相邻吸附形式.中性团簇和阴离子团簇的能量最低结构相似.稳定性分析表明TinO2具有很高的稳定性,特别是TiO2和Ti7O2.此外,详细讨论了团簇的电离势、电子亲和能、电子解离能和能隙.基于最低能量结构,讨论了团簇的磁性,发现电荷从Ti原子向O原子转移,并且电荷转移主要发生在TinO2的Ti-3d、Ti-4s和O-2p轨道.磁性团簇中反铁磁序占据主导,磁矩主要来源Ti-3d电子的贡献,而两个氧原子的贡献非常小.     

同核双原子分子及其阳离子的共价键结构比较

绘制了H2,H+2,B2,B+2,C2,C+2,O2,O+2,F2,F+2的电子密度图形,计算了所讨论分子的键长,电子组态及键鞍点处的电荷密度,形象直观地说明了双原子分子及其对应的阳离子的共价键结构。     

TinO2和TinO2-(n=1-10)团簇的几何结构、电子和磁性质

基于密度泛函理论(DFT)的B3LYP方法, 研究了Ti_nO₂和Ti_nO₂^- (n=1-10)团簇的几何结构、电子结构以及磁性. 结果表明, 两个氧以分离的原子状态吸附在金属团簇的表面, 呈现出以一个钛原子为中心的O-Ti-O 的相邻吸附形式. 中性团簇和阴离子团簇的能量最低结构相似. 稳定性分析表明Ti_nO₂具有很高的稳定性, 特别是TiO₂和Ti₇O₂. 此外, 详细讨论了团簇的电离势、电子亲和能、电子解离能和能隙. 基于最低能量结构, 讨论了团簇的磁性, 发现电荷从Ti 原子向O原子转移, 并且电荷转移主要发生在Ti_nO₂的Ti-3d、Ti-4s和O-2p轨道. 磁性团簇中反铁磁序占据主导, 磁矩主要来源Ti-3d电子的贡献, 而两个氧原子的贡献非常小.     

化学与环境污染(续)

水是一切生命机体的组成物质,为生命代谢活动所必需,又是人类进行生产活动的重要资源。生产和生活用水基本上都是淡水,而地球上的淡水只占总水量的0.63%。随着工农业生产的迅速发展,人口的大量增加和生活水平的提高,淡水消耗量急剧上升,若不节约用水,淡水将成为继石油危机之后的另一个社会危机。另外,人口的增加和工农业生产的发展又造成严重的水污染。我国的废水大部分未经处理直接排入江河湖海,使城市附近90%的水域受到不同程度的污染。在长江以北,除内陆河外,已经很难找到一条未被污染的河流。     

Anomalies in the Structural Chemistry of Silicon

In contrast to carbon, silicon fails to form multiple bonds that are stable at room temperature. Consequently molecules in which silicon exhibits coordination numbers (CN) of 1, 2, and 3 may only be obtained at very high or low temperatures. Under these conditions their structural features, including multiple bonds, resemble those of carbon. On the other hand, silicon is capable of forming various hexacoordinated compounds making use of its d orbitals. Nitrogen and oxygen bonded to silicon develop an unusual stereochemistry: planar nitrogen, nearly or completely linear oxygen, and considerable shortening of SiN, SiO, and SiF bonds are specific examples. N(SiR₃)₂ and CH₂SiR₃ ligands permit stabilization of unusually low CNs of many metals and give rise to amino and alkyl derivatives of unexpectedly high stability due to the particular electronic, the R₃Si group.     

Synthesis and Structural Chemistry of Tungstoarsenates(V)

An overview of the synthesis and of the structural chemistry of tungstoarsenates(V) of the 1:12 and 2:21 families is presented with special emphasis on the 2:20 species. The molecular structure of [As₂W₂₀O₇₁(H₂O)₃]¹²⁻ has been determined by single-crystal X-ray diffraction of K₁₂[As₂W₂₀O₇₁(H₂O)₃]·23H₂O and that of [As₂W₂₀O₇₀(H₂O)₂]¹⁰⁻ has been inferred from a ¹⁸³W NMR study in aqueous solution.This paper is dedicated to Professor Michael Pope in recognition of his invaluable contribution to polyoxometalate chemistry.     

准晶体的结构化学

介绍准晶体的历史、结构、对称性和性质,介绍Mg32(Al,Zn)49的晶体结构和对称性,同时讨论纳米准晶颗粒的制备方法及其应用。     

纳米化学(续)

7　针尖化学———在ＳＰＭ针尖上做文章　　针尖化学是北京大学纳米化学实验室于 1 997年提出的新概念。这里的针尖是指扫描探针显微镜的探针。ＳＴＭ和ＡＦＭ是强有力的表面成像工具 ,能够看到原子、分子水平的结构细节。但是 ,它们只能看到表面上有东西 ,并不知道是什么。换句话说 ,不具备“识别”能力。如果利用特殊的功能分子对针尖进行化学修饰 ,进行能动的分子设计 ,则有可能弥补ＳＰＭ这种“只认东西不识货”的不足。事实上 ,通过能动地设计针尖 ,能动地利用针尖 ,使其具有化学识别功能、化学响应功能、化学“透镜”功能等等 ,可以…     

物质结构教学中虚拟与实体模型的比较研究

本文研究比较虚拟与实体模型在中学化学物质结构教学中作用的目的,就是试图帮助学生建构正确的空间图像思维,尝试鼓励和引导学生建构正确的物质结构思维模式,这对于提高学生的思维品质有很大帮助。     

中性铜(Ⅰ)卤结构单元及其配位聚合物化学

铜(Ⅰ)卤簇合物的结构化学极其丰富多彩。一方面，以单齿或是多齿螯合型有机配体为辅助配体，铜(Ⅰ)卤自身可形成多种结构类型的孤立的簇或是低聚物，0维的如菱形的二聚体、立方烷型的或是椅式的四聚体，一维的如锯齿链或是楼梯链等等。若有机配体具有桥联性质，将桥联孤立的簇或是低聚物形成高维聚合物。本文以文献工作为主，结合自身工作，介绍有关中性铜(Ⅰ)卤簇化合物在结构方面的发展概况。     

Structural Chemistry of Poly(ethylene glycol) Complexes of Lead(II) Nitrate and Lead(II) Bromide

The reaction of 1:1 stoichiometries (1:1.5 for the nitrate/tetraethylene glycol (EO4) and pentaethylene glycol (EO5) complexes) of PbX(2) (X = NO(3), Br) with five- to eight-donor poly(ethylene glycols) (PEGs) in 3:1 CH(3)CN/CH(3)OH (CH(3)CN only for the nitrate/EO5 complex) followed by solvent evaporation resulted in six crystalline materials upon which X-ray structural analyses were carried out: [Pb(NO(3))(2)(EO4)](n)(), [Pb(NO(3))(2)(EO5)], [Pb(NO(3))(2)(EO6)], [PbBr(EO5)(&mgr;-Br)PbBr(2)].H(2)O, [PbBr(NCMe)(EO6)](2)[PbBr(2)(EO6)][PbBr(3)](2), and [PbBr(EO7)][PbBr(3)]. The nitrates crystallize as tight ion pairs with the PEG ligands coordinating in an equatorial plane around the Pb(2+) ions. Because EO4 has only five oxygen donors, this complex exhibits steric unsaturation which is overcome by a monodentate interaction with a third nitrate anion that is also coordinated to a neighboring Pb(2+) ion. The six donors of EO5 coordinate in an equatorial plane resulting in a 10-coordinate complex with trans, twisted, bidentate nitrate anions. The seven-donor hexaethylene glycol (EO6) only uses six of its oxygen donors to coordinate Pb(2+). [Pb(NO(3))(2)(EO4)](n)() is monoclinic, P2(1)/c, with a = 7.902(3) ?, b = 22.136(6) ?, c = 8.910(2) ?, beta = 90.96(3) degrees, and Z = 4. [Pb(NO(3))(2)(EO5)] is triclinic P&onemacr;, with a = 9.332(3) ?, b = 10.025(3) ?, c = 11.688(4) ?, alpha = 68.41(3) degrees, beta = 68.39(3) degrees, gamma = 68.58(3) degrees, and Z = 2. [Pb(NO(3))(2)(EO6)] is monoclinic P2(1)/c, with a = 16.289(4) ?, b = 10.773(4) ?, c = 12.329(4) ?, beta = 106.77(2) degrees, and Z = 4. Lead(II) bromide complexes with PEGs tend to crystallize as PEG complexed cations with polymeric lead(II) bromide anions. In the EO5 complex, bromide anions in the polymer also coordinate to the PEG-wrapped Pb(2+) cations. The hexa- and heptaethylene glycol (EO6 and EO7, respectively) complexes contain discreet ions. In these halide complexes, EO7 is the only PEG to expand the Pb(2+) coordination number from eight to nine. [PbBr(EO5)(&mgr;-Br)PbBr(2)].H(2)O is triclinic P&onemacr;, with a = 7.922(6) ?,b = 15.802(9) ?, c = 19.001(9) ?, alpha = 73.19(8) degrees, beta = 88.91(9) degrees, gamma = 87.22(9) degrees, and Z = 4. [PbBr(NCMe)(EO6)](2)[PbBr(2)(EO6)][PbBr(3)](2) is monoclinic P2(1)/c, with a = 14.389(4) ?, b = 31.931(9) ?, c = 8.029(2) ?, beta = 97.76(3) degrees, and Z = 2. [PbBr(EO7)][PbBr(3)] is monoclinic Cc, with a = 13.165(3) ?, b = 24.732(5) ?, c = 8.007(1) ?, beta = 94.58(2) degrees, and Z = 4.     

The twentieth year in Structural Chemistry

Twenty years ago our journal Structural Chemistry was founded with the primary purpose of providing a quality venue for reports that present the result of complex studies of chemical and biological systems and in the field of materials science, using diverse physical and computational techniques simultaneously and in a concerted way and that are concerned with the chemical, biological, and physical implications of the findings. A sampler of contributions witnesses the fulfillment of this goal and points justified expectations of a bright future for our publication.