BOUNDARY CONDITIONS FOR THE CATALYTIC PROPERTIES OF [MO-3FE-4S] CLUSTERS

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 本文提出用互补多边X射线吸收光谱研究立方烷型Mo/Fe/S团簇，以开发用于均相氮气还原的合成靶。这些靶标可以被认为是固氮酶的铁钼辅因子(FeMo-co)的仿生化合物。我们计划分三个阶段完成这项工作。首先，我们将使用硫化物、硒、二乙基二硫代氨基甲酸酯和二乙基二硒代氨基甲酸酯配体表征氧化和还原状态下具有系统变化的S和Se配体环境的立方烷型Mo/Fe/S簇合物。其次，我们将修饰铁周围的末端配体，以稳定铁的低价状态，由于簇核的亲核性增加，这些低价状态可能会激活氮。第三，我们扰动了Mo周围的配位环境，以彻底评估配位场对团簇的电子结构和几何结构的影响。我们计划利用XAS数据在Fe K-、Fe L-、Mo L-、ClK-、Se K-和S K边的互补性来产生未来团簇的理想结构性质。最近在BL4-3上发展的光束线现在允许收集S和氯EXAFS，它与Fe/Mo/S EXAFS相结合可以提供更可靠的几何结构拟合。对Fe L边和S K边的前缘和上升边特征的XANES分析提供了关于有效核电荷、金属/配体中心的氧化和自旋态、轨道组成、金属中心的配位场分裂以及配体可能的非无害行为的电子结构信息。利用Se的衍生物可以实现重叠的S K边和Mo L边的分离。除了制造新的仿生化合物的可能性外，从拟议的实验中获得的见解将对理解钼位在氮素活化中的有争议的作用产生影响。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We propose here complementary multi-edge X-ray absorption spectroscopic investigations of site-differentiated cubane-type Mo/Fe/S clusters for developing synthetic targets for homogeneous dinitrogen reduction processes. These targets can be considered as biomimetic compounds of the iron-molybdenum cofactor (FeMo-co) of nitrogenase. We plan to accomplish this in three stages. First, we will characterize cubane type Mo/Fe/S cluster with systematically varied S and Se ligand environments in oxidized and reduced states using sulfide, selenide, diethyldithio carbamate (DTC), and diethyldiseleno carbamate (DSC) ligands. Second, we will modify the terminal ligands around Fe targeting to stabilize low valent states of Fe that likely be poised toward activating dinitrogen because of the increased nucleophilicity of the cluster core. Third we perturb the coordination environments around Mo to thoroughly assess the ligand field effect on the electronic and geometric structures of the clusters. We plan to take advantage of complementarity of XAS data at the Fe K-, Fe L-, Mo L-, Cl K-, Se K- and S K-edges to generate desirable structural properties of future clusters. Recent beamline development at BL4-3 now allows for collection of S and Cl EXAFS, which in combination with Fe/Mo/S EXAFS can provide more reliable fits of geometric structure. XANES analysis of pre-edge and rising-edge features of Fe L-edge and S K-edge spectra provides electronic structural information about effective nuclear charges, oxidation and spin states of metal/ligand centers, orbital compositions, ligand-field splitting of metal centers, and possible non-innocent behavior of ligands. Separation of overlapping S K- and Mo L-edges will be achieved by utilizing Se derivatives. In addition to the potential of making new biomimetic compounds insights from the proposed experiments will have impact on the understanding of the controversial role of the Mo-site in activation of dinitrogen.