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Chirality at two-dimensional surfaces: A perspective from small molecule alcohol assembly on Au(111)
The Journal of Chemical Physics ( IF 4.4 ) Pub Date : 2018-07-18 , DOI: 10.1063/1.5035500
Melissa L. Liriano 1 , Amanda M. Larson 1 , Chiara Gattinoni 2 , Javier Carrasco 3 , Ashleigh E. Baber 1 , Emily A. Lewis 1 , Colin J. Murphy 1 , Timothy J. Lawton 1 , Matthew D. Marcinkowski 1 , Andrew J. Therrien 1 , Angelos Michaelides 2 , E. Charles H. Sykes 1
Affiliation  

The delicate balance between hydrogen bonding and van der Waals interactions determines the stability, structure, and chirality of many molecular and supramolecular aggregates weakly adsorbed on solid surfaces. Yet the inherent complexity of these systems makes their experimental study at the molecular level very challenging. In this quest, small alcohols adsorbed on metal surfaces have become a useful model system to gain fundamental insight into the interplay of such molecule-surface and molecule-molecule interactions. Here, through a combination of scanning tunneling microscopy and density functional theory, we compare and contrast the adsorption and self-assembly of a range of small alcohols from methanol to butanol on Au(111). We find that longer chained alcohols prefer to form zigzag chains held together by extended hydrogen bonded networks between adjacent molecules. When alcohols bind to a metal surface datively via one of the two lone electron pairs of the oxygen atom, they become chiral. Therefore, the chain structures are formed by a hydrogen-bonded network between adjacent molecules with alternating adsorbed chirality. These chain structures accommodate longer alkyl tails through larger unit cells, while the position of the hydroxyl group within the alcohol molecule can produce denser unit cells that maximize intermolecular interactions. Interestingly, when intrinsic chirality is introduced into the molecule as in the case of 2-butanol, the assembly changes completely and square packing structures with chiral pockets are observed. This is rationalized by the fact that the intrinsic chirality of the molecule directs the chirality of the adsorbed hydroxyl group meaning that heterochiral chain structures cannot form. Overall this study provides a general framework for understanding the effect of simple alcohol molecular adstructures on hydrogen bonded aggregates and paves the way for rationalizing 2D chiral supramolecular assembly.

中文翻译:

二维表面的手性:从Au(111)上的小分子醇组装的角度看

氢键和范德华相互作用之间的微妙平衡决定了许多弱吸附在固体表面上的分子和超分子聚集体的稳定性,结构和手性。然而,这些系统固有的复杂性使得它们在分子水平上的实验研究非常具有挑战性。在这一探索中,吸附在金属表面上的小醇已成为一种有用的模型系统,可从根本上洞悉此类分子-表面与分子-分子相互作用的相互作用。在这里,通过结合扫描隧道显微镜和密度泛函理论,我们比较并对比了从甲醇到丁醇的一系列小醇在Au(111)上的吸附和自组装。我们发现,较长链的醇倾向于形成由相邻分子之间扩展的氢键网络保持在一起的之字形链。当醇通过氧原子的两个孤对电子之一与金属表面固定结合时,它们将成为手性化合物。因此,链结构是由相邻分子之间具有交替吸附手性的氢键网络形成的。这些链结构通过较大的晶胞容纳更长的烷基尾部,而醇分子中羟基的位置可以产生致密的晶胞,从而使分子间的相互作用最大化。有趣的是,当像2-丁醇一样将固有手性引入分子中时,组装完全改变,并观察到带有手性口袋的方形堆积结构。这是由于分子的固有手性指导吸附的羟基的手性这一事实而合理的,这意味着不能形成杂手性链结构。总体而言,本研究为了解简单的醇分子结构对氢键键合聚集体的作用提供了一个总体框架,并为合理化二维手性超分子组装铺平了道路。
更新日期:2018-07-21
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