L-edge X-ray absorption spectroscopy of non-heme iron sites: Experimental determination of differential orbital covalency
L-edge X-ray absorption spectroscopy of non-heme iron sites: Experimental determination of differential orbital covalency
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DOI：
10.1021/ja034634s
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发表时间：
2003-10-22
影响因子：
15
通讯作者：
Solomon, EI
中科院分区：
文献类型：
--
作者：
Wasinger, EC;de Groot, FMF;Solomon, EI
X 射线吸收光谱已被用来获得一系列非血红素铁和亚铁络合物的 L 边多重光谱。利用这些数据，开发了一种确定总共价和差分轨道共价 (DOC) 的方法，即 d 轨道不同对称组中的共价差异。积分的 L 边强度与到未占据分子轨道的单电子跃迁路径的数量以及铁位点的共价性成正比，这降低了总 L 边强度并重新分布强度，产生震动卫星。此外，不同的轨道共价性导致不同对称性轨道组的强度差异，从而进一步修改实验光谱。通常用于模拟 L 边光谱的配体场多重态模型不能充分再现光谱特征，尤其是电荷转移卫星。包含具有共价差异的电荷转移态可以很好地拟合电荷转移震动路径对 t(2g) 和 e(g) 对称轨道的不同贡献的数据和实验估计。将实验确定的 DOC 与密度泛函理论计算的值进行比较，并用于了解不同共价环境的高自旋和低自旋亚铁和三价铁络合物的化学趋势。讨论了该方法在生物无机化学问题中的实用性。
X-ray absorption spectroscopy has been utilized to obtain the L-edge multiplet spectra for a series of non-heme ferric and ferrous complexes. Using these data, a methodology for determining the total covalency and the differential orbital covalency (DOC), that is, differences in covalency in the different symmetry sets of the d orbitals, has been developed. The integrated L-edge intensity is proportional to the number of one-electron transition pathways to the unoccupied molecular orbitals as well as to the covalency of the iron site, which reduces the total L-edge intensity and redistributes intensity, producing shake-up satellites. Furthermore, differential orbital covalency leads to differences in intensity for the different symmetry sets of orbitals and, thus, further modifies the experimental spectra. The ligand field multiplet model commonly used to simulate L-edge spectra does not adequately reproduce the spectral features, especially the charge transfer satellites. The inclusion of charge transfer states with differences in covalency gives excellent fits to the data and experimental estimates of the different contributions of charge transfer shake-up pathways to the t(2g) and e(g) symmetry orbitals. The resulting experimentally determined DOC is compared to values calculated from density functional theory and used to understand chemical trends in high- and low-spin ferrous and ferric complexes with different covalent environments. The utility of this method toward problems in bioinorganic chemistry is discussed.