Interaction of Iron–Sulfur Clusters with N2: Biomimetic Systems in the Gas Phase

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• 作者：Heiko C. Heim ; Thorsten M. Bernhardt ; Sandra M. Lang ; Robert N. Barnett ; Uzi Landman
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：June 16, 2016
• 年：2016
• 卷：120
• 期：23
• 页码：12549-12558
• 全文大小：529K
• 年卷期：0
• ISSN：1932-7455

文摘

The active centers of the nitrogen-fixing enzymes nitrogenases comprise iron–sulfur clusters. The binding of the substrate N₂ to these clusters plays a fundamental role for the subsequent ammonia synthesis. However, due to the complexity of the natural system and the lack of suitable synthetic models, the interaction of N₂ with the iron–sulfur clusters remains largely elusive. In this contribution, we demonstrate the gas-phase preparation and investigation of the cationic Fe₂S₂⁺, Fe₃S₃⁺, and Fe₄S₄⁺ clusters. These clusters represent the first cluster model systems containing more than one iron and sulfur atom, respectively, which are found to bind N₂. Temperature-dependent kinetic measurements allow, for the first time, for the determination of experimental binding energies of N₂ to iron–sulfur clusters. In addition, concurrent first-principles simulations reveal the ground state and isomeric structures of the iron–sulfur clusters with and without adsorbed N₂ and provide a conceptual understanding of the interaction between N₂ and iron–sulfur clusters. In particular, we present molecular level details of N₂ bonding such as the identification of the adsorption sites, the bond geometry, the bond strength, and the nature of the cluster-N₂ binding interaction, which is found to be promoted by occupation of the empty antibonding orbitals of the free N₂ molecule through interaction with the frontier orbitals of the iron–sulfur complex involving d-orbitals of iron hybridized with sulfur p-orbitals.