Pollock Christopher J, Lancaster Kyle M, Finkelstein Kenneth D, DeBeer Serena
Max-Planck-Institut für Chemische Energiekonversion , Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany.
Inorg Chem. 2014 Oct 6;53(19):10378-85. doi: 10.1021/ic501462y. Epub 2014 Sep 11.
Transition-metal Kβ X-ray emission spectroscopy (XES) is a developing technique that probes the occupied molecular orbitals of a metal complex. As an element-specific probe of metal centers, Kβ XES is finding increasing applications in catalytic and, in particular, bioinorganic systems. For the continued development of XES as a probe of these complex systems, however, the full range of factors which contribute to XES spectral modulations must be explored. In this report, an investigation of a series of oxo-bridged iron dimers reveals that the intensity of valence-to-core features is sensitive to the Fe-O-Fe bond angle. The intensity of these features has a well-known dependence on metal-ligand bond distance, but a dependence upon bond angle has not previously been documented. Herein, we explore the angular dependence of valence-to-core XES features both experimentally and computationally. Taken together, these results show that, as the Fe-O-Fe angle decreases, the intensity of the Kβ″ feature increases and that this effect is modulated by increasing amounts of Fe np mixing into the O 2s orbital at smaller bond angles. The relevance of these findings to the identification of oxygenated intermediates in bioinorganic systems is highlighted, with special emphasis given to the case of soluble methane monooxygenase.
过渡金属KβX射线发射光谱（XES）是一种正在发展的技术，用于探测金属配合物的占据分子轨道。作为一种针对金属中心的元素特异性探针，KβXES在催化领域，尤其是生物无机体系中的应用越来越广泛。然而，为了将XES持续发展为这些复杂体系的探针，必须探索导致XES光谱调制的所有因素。在本报告中，对一系列氧桥联铁二聚体的研究表明，价态到核心特征的强度对Fe-O-Fe键角敏感。这些特征的强度对金属-配体键距有众所周知的依赖性，但对键角的依赖性此前尚未见报道。在此，我们通过实验和计算探索价态到核心XES特征的角度依赖性。综合这些结果表明，随着Fe-O-Fe角减小，Kβ″特征的强度增加，并且在较小键角下，这种效应会因越来越多的Fe np混合到O 2s轨道而受到调制。强调了这些发现与生物无机体系中氧化中间体鉴定的相关性，特别关注了可溶性甲烷单加氧酶的情况。
