From local adsorption stresses to chiral surfaces:: (R,R)-tartaric acid on Ni(110)
From local adsorption stresses to chiral surfaces:: (R,R)-tartaric acid on Ni(110)
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DOI：
10.1021/ja012021e
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发表时间：
2002-01-23
影响因子：
15
通讯作者：
Raval, R
中科院分区：
文献类型：
--
作者：
Humblot, V;Haq, S;Raval, R
手性分子（R，R）-酒石酸吸附在镍表面产生高度对映选择性的非均相催化剂，但手性修饰的性质尚不清楚。在这里，我们报道了这种具有Ni（110）表面的手性分子的行为。结合反射吸收红外光谱、扫描隧道显微镜和周期密度泛函理论计算，揭示了一种新的手性感应模式。在室温和低覆盖率下，（R，R）-酒石酸通过两个羧酸基团以双酒石酸盐形式吸附在表面上。分子优先位于4倍中空位点上方，每个羧酸官能通过相邻Ni原子上方的0原子吸附在短桥位点上。然而，分子的手性OH基团与金属原子之间的排斥性相互作用导致在体截断Ni（l10）表面上发生严重的应变吸附。因此，最稳定的吸附结构是通过表面金属原子的显著弛豫来减轻这种吸附引起的应力，从而使表面上的Ni原子对之间可以容纳7.47 a的长距离。有趣的是，这导致成键的Ni原子在所有局部镜像对称面被破坏的表面上描述了一个手性足迹。计算表明（R，R）-酒石酸只对一个手性足迹有利，镜像吸附位点不稳定6 kJ mol（-1）。这种能量差足以使相同的局部手性重构和基序在系统的90%以上持续存在，从而导致整体高手性金属表面。
The chiral molecule (R,R)-tartaric acid adsorbed on nickel surfaces creates highly enantioselective heterogeneous catalysts, but the nature of chiral modification remains unknown. Here, we report on the behavior of this chiral molecule with a defined Ni(110) surface. A combination of reflection absorption infrared spectroscopy, scanning tunneling microscopy, and periodic density functional theory calculations reveals a new mode of chiral induction. At room temperatures and low coverages, (R,R)-tartaric acid is adsorbed in its bitartrate form with two-point bonding to the surface via both carboxylate groups. The molecule is preferentially located above the 4-fold hollow site with each carboxylate functionality adsorbed at the short bridge site via 0 atoms placed above adjacent Ni atoms. However, repulsive interactions between the chiral OH groups of the molecule and the metal atoms lead to severely strained adsorption on the bulk-truncation Ni(l 10) surface. As a result, the most stable adsorption structure is one in which this adsorption-induced stress is alleviated by significant relaxation of surface metal atoms so that a long distance of 7.47 A between pairs of Ni atoms can be accommodated at the surface. Interestingly, this leads the bonding Ni atoms to describe a chiral footprint at the surface for which all local mirror symmetry planes are destroyed. Calculations show only one chiral footprint to be favored by the (R,R)-tartaric acid, with the mirror adsorption site being unstable by 6 kJ mol(-1). This energy difference is sufficient to enable the same local chiral reconstruction and motif to be sustained over 90% of the system, leading to an overall highly chiral metal surface.