International Collaboration in Chemistry: Experimental and Theoretical Study of Redox-Active Fe4O4-Cubanes

这个项目是基于两个小组之间的合作，一个是实验的，一个是理论的，他们对高核度团簇中金属离子之间的相互作用有着共同的兴趣。这一提议是受到我们最近对八核铁簇[FeIII8(mu4-O)4(mu4-R-pz)12X4]的表征的启发，(PZ=吡唑类阴离子)，它包含一个Fe4O4立方烷核心，周围有四个FeIII中心。我们对这一特殊簇的着迷源于它们非凡的电化学性质：可以在比更广泛研究的铁/硫类似物更窄的电势窗口中访问四个可逆还原波。铁团簇适应电子计数的巨大波动的能力对于它们在生物电子转移中的作用是基本的，这些团簇为了解所涉及的亲密电子过程提供了一个独特的窗口。我们在最近的一份联合出版物中说明了这些体系中实验和理论之间的协同作用，其中我们分析了全铁母体化合物的结构和性质。最近，我们还成功地分离了1电子还原物种[FeIII8(mu4-O)4(mu4-R-pz)12X4]-。在这项提议中，我们寻求支持将我们的研究扩展到1-，2-，3-和4-电子还原类似物，所有这些类似物都具有铁和铁中心。最终目标是尽可能充分地描述在电化学实验中观察到的跨越FeIII8和FeII4FeII4极限的每一种混合价状态。波多黎各大学的重点将是合成能够支持更高度还原的氧化水平的新簇合物，并利用广泛的物理化学技术对其进行表征。伏安法、衍射法、原位UV-VIS-NIR光谱电化学和XPS将在内部进行，而磁化学性质、EPR和穆斯堡尔谱将在各自领域的领先合作伙伴的实验室中进行测量。格拉斯哥大学的研究小组将使用破缺对称密度泛函理论来探索这些化合物的电子结构。其目的是通过建立观测和基本电子结构之间的直接对应，最大限度地增加物理化学测量的信息含量。学术价值：混价金属物种的研究长期以来一直受到化学家的关注，金属中心之间的相互作用在材料和生物化学中都具有深远的意义。这项建议中描述的Fe8团簇提供了一个独特的机会来研究一个离散分子物种中前所未有的氧化态范围内的混合价态。这个项目将把波多黎各大学和格拉斯哥大学已建立的研究项目联系起来，这两所大学都侧重于顺磁金属星团的结构。这两个小组的方法相当不同，一个使用合成和物理化学测量，另一个理论，以及两者之间的协同作用有望揭示新的见解。青年研究人员有机会通过在国际实验室的长期停留来交流互补的想法和专业知识，这是研究方案的一个关键因素，无疑将在这两个群体之间建立长期的联系。申请者的非正式合作记录可以追溯到1990年代初，并已就与金属团簇的电子结构和性质有关的一些主题发表了联合论文。在所有情况下，这种合作都建立在光谱学和理论之间的协同作用上，这是这一提议的核心。

This project is based on a collaboration between two groups, one experimental and one theoretical, who share a common interest in the interaction between metal ions in high nuclearity clusters. The proposal has been inspired by our recent characterization of an octanuclear iron cluster, [FeIII8(mu4-O)4(mu-4-R-pz)12X4], (pz = the pyrazolato anion) which contains an Fe4O4 cubane core surrounded by four peripheral FeIII centers. Our fascination with this particular family of clusters stems from their remarkable electrochemical properties: four reversible reduction waves can be accessed in a potential window much narrower than anything seen for the more extensively-studied iron/sulfur analogues. The ability of iron clusters to accommodate large fluctuations in electron count is fundamental to their role in biological electron transfer, and these clusters offer a unique window on the intimate electronic processes involved. We have illustrated the synergy between experiment and theory in these systems in a recent joint publication, where we analyzed the structure and properties of the all-ferric parent compounds. Very recently, we have also succeeded in isolating the 1-electron reduced species, [FeIII8(mu4-O)4(mu-4-R-pz)12X4]-. In this proposal, we seek support to extend our studies to the 1-, 2-, 3- and 4-electron reduced analogues, all of which feature ferric and ferrous centers. The ultimate goal is to characterize as fully as possible each of the mixed-valent states spanning the FeIII8 and FeIII4FeII4 limits observed in the electrochemical experiment. The focus at the University of Puerto Rico will be on the synthesis of new clusters capable of supporting the more highly reduced oxidation levels and their characterization using a wide range of physicochemical techniques. Voltammetry, diffraction, in situ UV-Vis-NIR spectroelectrochemistry and XPS will be conducted 'in-house', while magnetochemical properties, EPR and Mssbauer spectra will be measured in the laboratories of established collaborators who are leaders in their fields. The research team at the University of Glasgow will explore the electronic structure of these compounds using broken-symmetry density functional theory. The aim is to maximize the information content of the physicochemical measurements by establishing a direct correspondence between observation and the underlying electronic structure. Intellectual merit: The study of mixed-valent metal species has long held the attention of chemists, and the interactions between the metal centers have profound implications in both materials and biological chemistry. The Fe8 clusters described in this proposal offer a unique opportunity to study mixed valence in a discrete molecular species across an unprecedented range of oxidation states. Much of the previous work in this area has been limited to di- or tetranuclear clusters, and the presence of eight paramagnetic centers presents a significant increase in complexity.This project will link established research programmes at the University of Puerto Rico and the University of Glasgow, both of which focus on the structure of paramagnetic metal clusters. The approaches of the two groups are quite distinct, one using synthesis and physicochemical measurements, the other theory, and the synergy between the two promises to reveal new insights. The opportunity for young researchers to exchange complementary ideas and expertise through extended stays in international laboratories is a key element of the research programme, and will undoubtedly establish long-lasting links between the two groups. The applicants have a track record of informal collaboration dating back to the early 1990s, and have already published joint papers on a number of topics related to the electronic structure and properties of metal clusters. In all cases, the collaboration has been founded on the synergy between spectroscopy and theory that lies at the heart of this proposal.