Molecular Dynamics and Surface Interactions of Nickelocene Adsorbed on Silica: A Paramagnetic Solid-State NMR Study
Molecular Dynamics and Surface Interactions of Nickelocene Adsorbed on Silica: A Paramagnetic Solid-State NMR Study
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二氧化硅上吸附的茂镍的分子动力学和表面相互作用：顺磁固态核磁共振研究
DOI：
10.1021/acs.langmuir.2c00301
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发表时间：
2022
期刊：
影响因子：
3.9
通讯作者：
Blümel, Janet
中科院分区：
文献类型：
--
作者：
Benzie, Jordon W.;Harmon-Welch, Gabrielle E.;Hoefler, John C.;Bakhmutov, Vladimir I.;Blümel, Janet
用二氧化硅在室温下无溶剂研磨二茂镍时，其吸附在孔内表面。这也通过在一个大的无色硅胶样品的孔隙中吸附绿色的茂镍得到了直观的证明。虽然这种孔内镍二世的干吸附和平移性已被直观地证明，但镍二世分子的点对点迁移性及其向表面的取向尚不清楚。在这个贡献中，介孔二氧化硅被用作这些问题的系统固态核磁共振研究的支持材料。顺磁固态核磁共振和弛豫时间是研究二氧化硅表面新镍动力学的有力工具。由此，可以在分子尺度上定量表征表面吸附的二茂镍分子在孔隙中的迁移率。根据获得的数据，二茂镍分子在表面上像液体一样运动。在具有亚单层表面覆盖的样品中，各向同性移动的分子与镍新世表面附着的分子状态迅速交换位置。这一发现得到了宏观可视化实验的证实。在温度低于200 K时，普遍存在的表面附着的水平取向镍二世分子的状态已被量化。ln(k)相对于1/T和ln（k/T）相对于1/T的速率坐标的温度依赖性形成了理想的直线，可以确定动力学参数seact = 5.5 kcal/mol，A= 1.1 × 1010， ΔH‡= 5.0 kcal/mol， ΔS‡=−15 eu。研究了一种具有相同数量的二茂镍和二茂铁的样品，其亚单层表面覆盖率为80%，表明不同的茂金属在二氧化硅表面的分子水平上混合。
When grinding nickelocene with silica in the absence of a solvent at room temperature, it adsorbs on the surface within the pores. This has also been demonstrated visually by adsorbing green nickelocene in the pores of a large colorless silica gel specimen. While this dry adsorption and translational mobility of nickelocene within the pores is proven visually, the site-to-site mobility of the nickelocene molecules and their orientation toward the surface are not yet understood. In this contribution, mesoporous silica is used as the support material for a systematic solid-state NMR study of these issues. Paramagnetic1H VT solid-state NMR andT1relaxation times have been powerful tools for studying the dynamics of nickelocene on the silica surface. Herewith, the mobility of the surface-adsorbed nickelocene molecules in the pores could be quantified on the molecular scale. According to the obtained data, the nickelocene molecules move like a liquid on the surface. Isotropically moving molecules exchange places rapidly with surface-attached molecular states of nickelocene in a sample with submonolayer surface coverage. This finding is corroborated by a macroscopic visualization experiment. The states of the surface-attached horizontally oriented nickelocene molecules that are prevalent at temperatures below 200 K have been quantified. The temperature dependencies of the ratekin coordinates of ln(k) versus 1/Tand ln(k/T) versus 1/Tform ideal straight lines that allow the determination of the kinetic parametersEact= 5.5 kcal/mol,A= 1.1 × 1010, ΔH‡= 5.0 kcal/mol, and ΔS‡= −15 eu. Investigating a sample with equal amounts of nickelocene and ferrocene in a submonolayer amount of 80% overall surface coverage shows that the different metallocenes mix on the molecular level on the silica surface.