在金属有机框架系统中,分子"配对"相互作用与不和金属中心 (MOF-74) 相互作用
Nour Nijem1, Jean-François Veyan, Lingzhu Kong
1Department of Materials Science & Engineering, University of Texas at Dallas, Richardson, Texas 75080, United States.
Journal of the American Chemical Society
|October 8, 2010
概括
红外光谱学揭示了MOF-74-M中的分子 (H2) 相互作用. 由于H2-H2相互作用而发生更大的H2转移,而不仅仅是金属结合,使吸附能量的计算复杂化.
科学领域:
- 材料科学 材料科学 材料科学
- 频谱学是一种光谱学.
- 物理化学 物理化学
背景情况:
- 金属有机框架 (MOFs),特别是MOF-74-M,正在研究它们与分子 (H2) 的相互作用.
- 以前的研究表明,MOF中的H2吸附能量与其振动频率的变化有关.
- 众所周知,MOF中的不和金属中心与H2强烈相互作用.
研究的目的:
- 用红外 (IR) 吸收光谱学研究MOF-74-M中H2与不和金属中心相互作用的性质.
- 了解影响吸附H2的振动转移的因素.
- 评估可变温度红外光谱学在确定吸附能量的有用性.
主要方法:
- 红外 (红外) 吸收光谱检测在MOF-74-M上用吸附的H2在不同温度 (20-200K和300K) 和压力 (高达60bar) 上进行.
- 对H2振动拉伸频率转移的分析.
- 与现有数据和理论计算进行比较.
主要成果:
- 在较低的H2负荷下,在金属位点上吸附时,观察到H2拉伸频率的小变化 (∼-30 cm-1).
- 只有当邻近位置被占用时,才会发生较大的移位 (∼-70 cm-1),这表明H2-H2相互作用,而不仅仅是金属-H2结合.
- 发现振动转移对局部环境和H2-H2相互作用敏感,与结合能没有直接相关性.
结论:
- 在MOF-74-M中H2的振动转移主要受到邻近地点的H2-H2相互作用的影响,而不是仅仅由金属中心的吸附能量影响.
- 这一发现挑战了假设红外振动转移与这些系统中的吸附能直接相关的假设.
- 这些因素的复杂相互作用使得使用可变温度的红外光谱来精确计算特定地点的吸附能量变得更加复杂.
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