Metal鈥揕igand Covalency of Iron Complexes from High-Resolution Resonant Inelastic X-ray Scattering

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• 作者：Marcus Lundberg ; Thomas Kroll ; Serena DeBeer ; Uwe Bergmann ; Samuel A. Wilson ; Pieter Glatzel ; Dennis Nordlund ; Britt Hedman ; Keith O. Hodgson ; Edward I. Solomon
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：November 13, 2013
• 年：2013
• 卷：135
• 期：45
• 页码：17121-17134
• 全文大小：697K
• 年卷期：v.135,no.45(November 13, 2013)
• ISSN：1520-5126

文摘

Data from K伪 resonant inelastic X-ray scattering (RIXS) have been used to extract electronic structure information, i.e., the covalency of metal鈥搇igand bonds, for four iron complexes using an experimentally based theoretical model. K伪 RIXS involves resonant 1s鈫?d excitation and detection of the 2p鈫?s (K伪) emission. This two-photon process reaches similar final states as single-photon L-edge (2p鈫?d) X-ray absorption spectroscopy (XAS), but involves only hard X-rays and can therefore be used to get high-resolution L-edge-like spectra for metal proteins, solution catalysts and their intermediates. To analyze the information content of K伪 RIXS spectra, data have been collected for four characteristic 蟽-donor and 蟺-back-donation complexes: ferrous tacn [Fe^II(tacn)₂]Br₂, ferrocyanide [Fe^II(CN)₆]K₄, ferric tacn [Fe^III(tacn)₂]Br₃ and ferricyanide [Fe^III(CN)₆]K₃. From these spectra metal鈥搇igand covalencies can be extracted using a charge-transfer multiplet model, without previous information from the L-edge XAS experiment. A direct comparison of L-edge XAS and K伪 RIXS spectra show that the latter reaches additional final states, e.g., when exciting into the e_g (蟽*) orbitals, and the splitting between final states of different symmetry provides an extra dimension that makes K伪 RIXS a more sensitive probe of 蟽-bonding. Another key difference between L-edge XAS and K伪 RIXS is the 蟺-back-bonding features in ferro- and ferricyanide that are significantly more intense in L-edge XAS compared to K伪 RIXS. This shows that two methods are complementary in assigning electronic structure. The K伪 RIXS approach can thus be used as a stand-alone method, in combination with L-edge XAS for strongly covalent systems that are difficult to probe by UV/vis spectroscopy, or as an extension to conventional absorption spectroscopy for a wide range of transition metal enzymes and catalysts.