Sensitivity of X-ray Core Spectroscopy to Changes in Metal Ligation: A Systematic Study of Low-Coordinate, High-Spin Ferrous Complexes
Sensitivity of X-ray Core Spectroscopy to Changes in Metal Ligation: A Systematic Study of Low-Coordinate, High-Spin Ferrous Complexes
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DOI：
10.1021/ic3021723
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发表时间：
2013-06-03
影响因子：
4.6
通讯作者：
DeBeer, Serena
中科院分区：
文献类型：
--
作者：
Chandrasekaran, P.;Chiang, Karen P.;DeBeer, Serena
为了评价X射线吸收和发射光谱测定金属配位球变化的灵敏度和互补性，对铁模型配合物进行了系统的实验和理论研究。[（LFe）-Fe-tBu（SPh）]（1）（其中L-tBu =大体积β-二酮亚胺配体; SPh =苯基硫醇盐）合成四个配位络合物[（LFe）-Fe-tBu（SPh）（X）]（其中X =（CNBu）-Bu-t（2）; 1-甲基咪唑（3）;或N，N-二甲基甲酰胺（DMF）（4）），已使用Fe K边X射线吸收（XAS）和K β X射线发射（XES）光谱的组合进行了研究。的Fe K XAS前边缘和边缘的所有四个配合物是一致的高自旋亚铁分配，与前边缘强度的最大差异归因于第四配位位点的共价性的变化。X-射线发射光谱显示显着的变化的价核心区域（V2 C）的身份的配位体是不同的。将实验结果与密度泛函理论（DFT）计算相关联，以了解分子轨道对所观察到的吸收和发射特征的贡献。计算还被扩展到一系列假设的高自旋铁配合物，以了解XAS和XES技术对不同配体质子化状态（[（LFeII）-Fe-tBu（SPh）（NHn）]（3-n）的敏感性。（n = 3，2，1，0））、金属氧化态[（LFe）-Fe-tBu（SPh）（N）]（n-）（n = 3，2，1）和配体身份的变化[（LFeIV）-Fe-tBu（SPh）（X）]（n-）（X = C4-、N3-、O2-; n = 2，1，0）。这项研究表明，XAS前边缘的数据有更大的灵敏度，氧化态的变化，而价核（V2 C）XES数据提供了一个更敏感的探针配体身份和质子化状态。因此，多种X射线光谱方法与DFT结果相结合，有可能在化学和生物催化中提供复杂无机体系的详细表征。
In order to assess the sensitivity and complementarity of X-ray absorption and emission spectroscopies for determining changes in the metal ligation sphere, a systematic experimental and theoretical study of iron model complexes has been carried out A series of high spin ferrous complexes, in which the ligation sphere has been varied from a three coordinate complex, [(LFe)-Fe-tBu(SPh)] (1) (where L-tBu = bulky beta-diketiminate ligand; SPh = phenyl thiolate) to four coordinate complexes [(LFe)-Fe-tBu(SPh)(X)] (where X = (CNBu)-Bu-t (2); 1-methylimidazole (3); or N,N-dimethylformamide (DMF) (4)), has been investigated using a combination of Fe K-edge X-ray absorption (XAS) and K beta X-ray emission (XES) spectroscopies. The Fe K XAS pre-edge and edge of all four complexes are consistent with a high spin ferrous assignment, with the largest differences in the pre-edge intensities attributed to changes in covalency of the fourth coordination site The X-ray emission spectra show pronounced changes in the valence to core region (V2C) as the identity of the coordinated ligand is varied. The experimental results have been correlated to density functional theory (DFT) calculations, to understand key molecular orbital contributions to the observed absorption and emission features The calculations also have been extended to a series of hypothetical high spin iron complexes to understand the sensitivity of XAS and XES techniques to different ligand protonation states ([(LFeII)-Fe-tBu(SPh)(NHn)](3-n) (n = 3, 2, 1, 0)), metal oxidation states [(LFe)-Fe-tBu(SPh)(N)](n-) (n = 3, 2, 1), and changes in the ligand identity [(LFeIV)-Fe-tBu(SPh)(X)](n-) (X = C4-, N3-, O2-; n = 2, 1, 0). This study demonstrates that XAS pre-edge data have greater sensitivity to changes in oxidation state, while valence to core (V2C) XES data provide a more sensitive probe of ligand identity and protonation state. The combination of multiple X-ray spectroscopic methods with DFT results thus has the potential to provide for detailed characterization of complex inorganic systems in both chemical and biological catalysis.