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

该子项目是利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 中心，不一定是研究者的机构。 在这里，我们提出了互补的多边缘X-射线吸收光谱调查的网站分化立方烷型Mo/Fe/S集群开发合成目标均匀二氮还原过程。这些靶标可以被认为是固氮酶铁钼辅因子（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，我们将表征立方烷型Mo/Fe/S簇与系统不同的S和Se配体环境中的氧化和还原状态，使用硫化物，硒化物，二乙基二硫代氨基甲酸酯（DTC），和二乙基二硒代氨基甲酸酯（DSC）配体。第二，我们将修改铁靶向周围的末端配体，以稳定可能由于簇核心的亲核性增加而倾向于活化二氮的低价态铁。第三，我们扰动钼周围的配位环境，以彻底评估配位场对簇的电子和几何结构的影响。我们计划利用XAS数据在Fe K-，Fe L-，Mo L-，Cl K-，Se K-和S K-边缘的互补性来产生未来簇的理想结构特性。BL 4 -3最近的光束线发展现在允许收集S和Cl EXAFS，其与Fe/Mo/S EXAFS结合可以提供更可靠的几何结构拟合。Fe L边和S K边光谱的前边缘和上升边缘特征的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状态、轨道组成、金属中心的配体场分裂以及配体的可能的非无辜行为的电子结构信息。重叠的S K-和Mo L-边缘的分离将通过利用Se衍生物来实现。除了潜在的制造新的仿生化合物的见解，从拟议的实验将有影响的理解有争议的作用的Mo-网站在激活双氮。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 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.