溶液与固态结构对比的伊特尔异金属催化剂的溶液
Lorenzo Di Bari1, Moreno Lelli, Guido Pintacuda
1ICCOM-CNR, Sez. di Pisa, Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, I-56126 Pisa, Italy.
Journal of the American Chemical Society
|May 2, 2003
概括
这项研究揭示了异金属复合物的溶液结构,发现它们具有相似的几何形状,但在磁性特性上有所不同. 接近红外线的圆形二极化证明对协调球的变化很敏感.
科学领域:
- 有机金属化学 有机金属化学
- 催化剂是一种催化剂.
- 频谱学是一种光谱学.
背景情况:
- 包括Na(3) [Yb(((S) -BINOL) ((3) ],K(3) [Yb((S) -BINOL) ((3) ]和Li(3) [Yb((S) -BINOL) ((3) ]在内的伊特异金属复合物是公认的反选择性催化剂.
- 了解它们的溶液结构对于优化催化性能至关重要.
研究的目的:
- 为了阐明 ytterbium 异金属复合物的溶液结构.
- 研究从晶体状态溶解后的结构动态.
- 评估光谱技术对协调球变化的敏感性.
主要方法:
- 核磁共振 (NMR) 光谱,包括偏磁转移.
- 紫外线和近红外线 (NIR) 圆形二极化 (CD) 光谱学.
- 用X射线衍射 (XRD) 进行晶体结构比较.
- 交换光谱 (EXSY) 用于研究债券流动性.
主要成果:
- 综合体1,2,3具有相同的溶液几何形状,但具有不同的磁性易感性异构 (D) 因素.
- 对复合物1在溶解时观察到从晶体C(3) 到溶液D(3) 对称性的结构重组.
- 在溶液中没有检测到与水的氧键,而Ln-BINOL键显示出可变性.
- NIR-CD光谱对协调环境的变化非常敏感.
结论:
- 这些复合体的溶液结构在不同区域 (Na+,K+,Li+) 保存.
- 溶解会诱导从晶体状态到溶液状态的对称性变化.
- Ln-BINOL键的可变性和缺少水协调是溶液状态的关键特征.
- 在这些催化系统中,NIR-CD是一种强大的工具,可以探测这些催化系统中的协调球.
相关概念视频
02:50Catalysis
The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
02:34Structural Isomerism
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
02:42Valence Bond Theory
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
01:27Catalysis
Catalysis influences the rate of chemical reactions by providing an alternative reaction pathway with lower activation energy. A catalyst speeds up a reaction, but it is not consumed during the process. The fundamental principle of catalysis is the ability of a catalyst to alter the reaction mechanism, often introducing a more efficient pathway than the uncatalyzed process.In a catalyzed reaction, the catalyst participates directly in the reaction mechanism. It interacts with reactants to form...
01:22Heterogeneous Catalysis
Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...