Čendak Tomaž, Sequeira Lisa, Sardo Mariana, Valente Anabela, Pinto Moisés L, Mafra Luís
CICECO-Chemistry Department, University of Aveiro, Campus de Santiago, 3810-193, Aveiro, Portugal.
National Institute of Chemistry, Hajdrihova 19, 1001, Ljubljana, Slovenia.
Chemistry. 2018 Jul 17;24(40):10136-10145. doi: 10.1002/chem.201800930. Epub 2018 Jun 13.
The wealth of site-selective structural information on CO speciation, obtained by spectroscopic techniques, is often hampered by the lack of easy-to-control synthetic routes. Herein, an alternative experimental protocol that relies on the high sensitivity of C chemical shift anisotropy (CSA) tensors to proton transfer, is presented to unambiguously distinguish between ionic/charged and neutral CO species, formed upon adsorption of CO in amine-modified porous materials. Control of the surface amine spacing was achieved through the use of amine protecting groups during functionalisation prior to CO adsorption. This approach enabled the formation of either "isolated" or "paired" carbamate/carbamic acid species, providing a first experimental NMR proof towards the identification of both aggregation states. Computer modelling of surface CO -amine adducts assisted the solid-state NMR assignments and validated various hydrogen-bond arrangements occurring upon formation of isolated/aggregated carbamic acid and alkylammonium carbamate ion species. This work extends the understanding of chemisorbed CO structures formed at pore surfaces and reveals structural insight about the protonation source responsible for the proton-transfer mechanism in such aggregates.
通过光谱技术获得的关于CO形态的大量位点选择性结构信息，常常因缺乏易于控制的合成路线而受到阻碍。在此，我们提出了一种替代实验方案，该方案依赖于¹³C化学位移各向异性（CSA）张量对质子转移的高灵敏度，以明确区分在胺改性多孔材料中吸附CO时形成的离子/带电和中性CO物种。在CO吸附之前的功能化过程中，通过使用胺保护基团来控制表面胺间距。这种方法能够形成“孤立”或“成对”的氨基甲酸酯/氨基甲酸物种，为识别这两种聚集状态提供了首个实验性NMR证据。表面CO-胺加合物的计算机建模辅助了固态NMR归属，并验证了在孤立/聚集的氨基甲酸和烷基铵氨基甲酸酯离子物种形成时出现的各种氢键排列。这项工作扩展了对孔表面形成的化学吸附CO结构的理解，并揭示了关于此类聚集体中质子转移机制的质子化来源的结构见解。
