Nitrogen fixation is a vital process for both nature and industry. Whereas the nitrogenase can reduce nitrogen in ambient environment in nature, the industrialized Haber-Bosch process is a high temperature and high-pressure process. Since the discovery of the first dinitrogen complex in 1965, many dinitrogen complexes are prepared in a homogeneous solution to mimic the nitrogenase enzyme in nature. However, studies of the heterogeneous process on surface are rarely addressed. Moreover, molecular scale characterization for such dinitrogen complex is lacking. Here, we present a simple model system to investigate, at the single-molecule level, the binding of dinitrogen on a surface confined iron phthalocyanine (FePc) monolayer through the combination of in-situ low-temperature scanning tunneling microscopy (LT-STM) and X-ray photoelectron spectroscopy (XPS) measurements. The iron center in FePc molecule deposited on Au(111) and highly oriented pyrolytic graphite (HOPG) surface can adsorb dinitrogen molecule at room temperature and low pressure. A comparative study reveals that the adsorption behaviors of FePc on these two different substrates are identical. Chemical bond is formed between the dinitrogen and the Fe atom in the FePc molecule, which greatly modifies the electronic structure of FePc. The bonding is reversible and can be manipulated by applying bias using a STM tip or by thermal annealing.

固氮对于自然界和工业界都是至关重要的过程。固氮酶可以自然还原周围环境中的氮，而工业化的Haber-Bosch工艺是高温高压工艺。自1965年发现第一个二氮配合物以来，许多二氮配合物是在均质溶液中制备的，以模拟自然界中的固氮酶。然而，很少研究表面上的异质过程。而且，缺乏这种二氮配合物的分子尺度表征。在这里，我们提出了一个简单的模型系统，以在单分子水平上通过原位结合研究表面约束铁酞菁铁（FePc）单层上二氮的结合低温扫描隧道显微镜（LT-STM）和X射线光电子能谱（XPS）测量。FePc分子中的铁中心沉积在Au（111）和高度取向的热解石墨（HOPG）表面上，可以在室温和低压下吸附二氮分子。一项比较研究表明，FePc在这两种不同基质上的吸附行为是相同的。FePc分子中的二氮与Fe原子之间形成化学键，极大地改变了FePc的电子结构。结合是可逆的，可以通过使用STM尖端施加偏压或通过热退火来操纵。