Electronic structure and spectroscopy of "superoxidized" iron centers in model systems: theoretical and experimental trends
Electronic structure and spectroscopy of "superoxidized" iron centers in model systems: theoretical and experimental trends
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DOI：
10.1039/b801803k
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发表时间：
2008-01-01
影响因子：
3.3
通讯作者：
Neese, Frank
中科院分区：
文献类型：
--
作者：
Berry, John F.;George, Serena DeBeer;Neese, Frank
合成化学的最新进展导致了具有价态Fe（V）和Fe（VI）的“超氧化”铁中心的发现[K]。Meyer等人，J. Am.化学会，1999，121，4859 - 4876; J. F. Berry等人，Science，2006，312，1937 - 1941; F. T. de Oliveira等人，Science，2007，315，835 - 838.]。此外，近年来发现了许多高价Fe（IV）物种作为金属酶的反应中间体，并且还在模型系统中进行了表征[C. Krebs等人，Acc. Chem. Res.，2007，40，484-492; L. Que，Jr，Acc. Chem. Res.，2007，40，493 - 500.]。这些物质几乎总是由高碱性配体Xn稳定，Xn是O2-或N3-。我是督察。作为氧化态的函数的氧代-和氮代物种之间的结构和键合的增强以及它们对可观察的光谱性质的影响从未被仔细评估。因此，基本的。本文计算了一系列假想的反式[FeO（NH3）（4）OH]（+/2+/3+）（1-3）和反式-[FeN（NH3）4 OH]（0/2+/3+）（4-6）配合物中Fe=O或Fe=N重键的高价铁配合物之间的相互作用。与Fe=O键相比，Fe=N多重键本质上更具共价性，所有计算性质都渗透其中。这个迪。这可能是由于差异。在N和O之间的Z* 中，这允许在FeQN多重键的情况下发生更好的轨道重叠。自旋态能量学是使用精细的多参考从头计算来解决的，该计算表明，所有种类1-6都具有对低自旋态的固有偏好，除了在1的情况下，其中S = 1和S = 2态在能量上非常接近。除了穆斯堡尔参数，g张量，零场分裂和铁超。本文用含时密度泛函方法模拟了X射线吸收Fe K前沿谱。一系列化合物的第一次跨越高价态+4，+5和+6铁。已经发现这些模拟的前边缘特征与孤立高价中间体的实验数据具有非常好的相关性，使我们能够将主要的前边缘特征分配给进入空Fe d（z 2）轨道的激发，该空Fe d（z 2）轨道能够与Fe 4（pz）混合，从而允许e.强度的有效机制。前边缘特征的阳离子。
Recent advances in synthetic chemistry have led to the discovery of "superoxidized'' iron centers with valencies Fe( V) and Fe( VI) [K. Meyer et al., J. Am. Chem. Soc., 1999, 121, 4859 - 4876; J. F. Berry et al., Science, 2006, 312, 1937 - 1941; F. T. de Oliveira et al., Science, 2007, 315, 835 - 838.]. Furthermore, in recent years a number of high- valent Fe(IV) species have been found as reaction intermediates in metalloenzymes and have also been characterized in model systems [C. Krebs et al., Acc. Chem. Res., 2007, 40, 484-492; L. Que, Jr, Acc. Chem. Res., 2007, 40, 493 - 500.]. These species are almost invariably stabilized by a highly basic ligand Xn- which is either O2- or N3-. The di. erences in structure and bonding between oxo- and nitrido species as a function of oxidation state and their consequences on the observable spectroscopic properties have never been carefully assessed. Hence, fundamental di. erences between high- valent iron complexes having either Fe=O or Fe=N multiple bonds have been probed computationally in this work in a series of hypothetical trans[FeO(NH3)(4)OH](+/2+/3+) (1-3) and trans-[FeN(NH3) 4OH](0/2+/3+) (4-6) complexes. All computational properties are permeated by the intrinsically more covalent character of the Fe=N multiple bond as compared to the Fe=O bond. This di. erence is likely due to di. erences in Z* between N and O that allow for better orbital overlap to occur in the case of the FeQN multiple bond. Spin- state energetics were addressed using elaborate multireference ab initio computations that show that all species 1-6 have an intrinsic preference for the low-spin state, except in the case of 1 in which S = 1 and S = 2 states are very close in energy. In addition to Mossbauer parameters, g-tensors, zero-field splitting and iron hyper. ne couplings, X- ray absorption Fe K pre-edge spectra have been simulated using time- dependent DFT methods for the. rst time for a series of compounds spanning the highvalent states +4, +5, and +6 for iron. A remarkably good correlation of these simulated pre- edge features with experimental data on isolated high- valent intermediates has been found, allowing us to assign the main pre-edge features to excitations into the empty Fe d(z2) orbital, which is able to mix with Fe 4(pz), allowing an e. cient mechanism for the intensi. cation of pre-edge features.