在十甲基氨基烯离子体中的 anisotropic NMR相互作用张量
Robert W Schurko1, Ivan Hung, Charles L B Macdonald
1Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4. rschurko@uwindsor.ca
Journal of the American Chemical Society
|October 31, 2002
概括
双 (pentamethylcyclopentadienyl) 离子,[Cp(2) Al](+),具有很高的对称性,类似于铁. 核磁共振和计算方法揭示了它的结构,动态环旋转和异型核磁共振相互作用,证实了它的独特特性.
科学领域:
- 有机金属化学 有机金属化学
- 固态核磁共振 (NMR) 光谱学 固态核磁共振 (NMR) 光谱
- 计算化学计算化学
背景情况:
- 主组金属,如二甲 (pentamethylcyclopentadienyl) 酸 ([Cp(2) Al] ((+)),在结构上类似于过渡金属金属,如铁.
- 了解这些化合物的分子结构和电子特性对于推进主要组化学至关重要.
- 无极性NMR相互作用张量器提供了对当地的电子环境和分子对称性的详细见解.
研究的目的:
- 综合描述 bis(pentamethylcyclopentadienyl) 离子 ([Cp(2) Al] ((+)) 的分子结构和异构性NMR相互作用张量.
- 为了研究动态行为,特别是环旋转,在[Cp(2) Al](+) 电位内.
- 将实验性NMR数据与理论计算相关联,以了解观察到的NMR相互作用的起源.
主要方法:
- 固态核磁共振 (NMR) 实验,包括27Al[(1) H]神奇角旋转 (MAS) 和静态NMR,以及13C CPMAS NMR.
- 单晶X射线衍射用于[Cp(2) Al][AlCl(4) ]的结构确定.
- 最初的自一致场 (SCF) 和混合密度函数理论 (DFT) 计算,以及NMR粉末模式的分析和数值模拟.
主要成果:
- 确定了[Cp(2) Al][AlCl(4) ]的单晶X射线衍射结构.
- 固态27Al NMR揭示了轴对称的化学屏蔽和电场梯度张量,具有很大的化学屏蔽跨度 (Omega = 83(3) ppm) 和一个小的核四极合常量 (C(Q) (((27) Al) = 0.86(10) MHz).
- 13C NMR 实验和计算表明,甲基cyclopentadienyl 环的动态旋转具有较低的内部旋转屏障.
结论:
- 双 (pentamethylcyclopentadienyl) 离子 ([Cp(2) Al](+)) 具有高分子对称性,与其与铁素的结构相似.
- 实验和理论数据非常一致,为NMR相互作用的分子起源提供了洞察力.
- 观察到的NMR参数,包括大化学屏蔽跨度和小四极合常数,通过[Cp(2) Al](+) 离子的高对称性得到合理化.
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