Two- and Three-Electron Oxidation of Single-Site Vanadium Centers at Surfaces by Ligand Design.
Two- and Three-Electron Oxidation of Single-Site Vanadium Centers at Surfaces by Ligand Design.
复制标题
通过配体设计对表面单点钒中心进行二电子和三电子氧化。
DOI：
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发表时间：
2015
影响因子：
15
通讯作者：
S. Tait
中科院分区：
文献类型：
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作者：
D. Skomski;Christopher D. Tempas;Brian J Cook;A. Polezhaev;Kevin A. Smith;K. G. Caulton;S. Tait
合理、系统地调节表面上的单位金属中心为提高多相催化反应的选择性提供了新的途径。虽然已经实现了这种均匀氧化态的金属中心，但还没有显示出通过使用精心设计的配体来控制其氧化态的能力。为此，由两个吡啶基或嘧啶取代基功能化的四嗪配体与金属钒一起沉积在Au(100)表面。X-射线光电子能谱表明，与V(2+)配对时相比，双嘧啶四嗪具有更强的氧化能力，有利于V(3+)在表面形成氧化还原。这证明了通过改变有机配体的氧化还原性质来控制表面配位结构中的金属氧化态的能力。金属-配体络合物以一维聚合链的形式存在，通过扫描隧道显微镜进行分辨。第一层中的链结构非常均匀，并且以相同的准正方形平面配位几何构型为基础，无论是哪一种配体，都围绕着单位V。在第二层形成的早期阶段观察到不同的二聚体结构的形成。这些体系为控制单位过渡金属原子在表面的氧化状态提供了新的机会，为多相催化剂的新进展提供了新的途径。
Rational, systematic tuning of single-site metal centers on surfaces offers a new approach to increase selectivity in heterogeneous catalysis reactions. Although such metal centers of uniform oxidation states have been achieved, the ability to control their oxidation states through the use of carefully designed ligands had not been shown. To this end, tetrazine ligands functionalized by two pyridinyl or pyrimidinyl substituents were deposited, along with vanadium metal, on the Au(100) surface. The greater oxidizing power of the bis-pyrimidinyltetrazine facilitates the on-surface redox formation of V(3+), compared to V(2+) when paired with the bis-pyridinyltetrazine, as determined by X-ray photoelectron spectroscopy. This demonstrates the ability to control metal oxidation states in surface coordination architectures by altering the redox properties of organic ligands. The metal-ligand complexes take the form of one-dimensional polymeric chains, resolved by scanning tunneling microscopy. The chain structures in the first layer are very uniform and are based on the same quasi-square-planar coordination geometry around single-site V with either ligand. Formation of a different, dimer structure is observed in the early stages of the second layer formation. These systems offer new opportunities in controlling the oxidation state of single-site transition metal atoms at a surface for new advances in heterogeneous catalysts.