Mn K-edge XANES and Kbeta XES studies of two Mn-oxo binuclear complexes: investigation of three different oxidation states relevant to the oxygen-evolving complex of photosystem II.
Mn K-edge XANES and Kbeta XES studies of two Mn-oxo binuclear complexes: investigation of three different oxidation states relevant to the oxygen-evolving complex of photosystem II.
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DOI：
10.1021/ja004306h
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发表时间：
2001-07
影响因子：
15
通讯作者：
H. Visser;E. Anxolabéhère‐Mallart;U. Bergmann;P. Glatzel;J. Robblee;S. Cramer;J. Girerd;K. Sauer;M. Klein;V. Yachandra
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文献类型：
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作者：
H. Visser;E. Anxolabéhère‐Mallart;U. Bergmann;P. Glatzel;J. Robblee;S. Cramer;J. Girerd;K. Sauer;M. Klein;V. Yachandra
研究了两种不同氧化态的结构同源Mn化合物，考察了氧化态和配体环境对Mn K边X射线吸收近边结构（XANES）和Mn K β X射线发射光谱（Kbeta XES）的相对影响.这两种锰化合物是二-μ-氧代化合物[L ′ 2 Mn（III）O 2 Mn（IV）L ′ 2]（ClO 4）3，其中L ′是1，10-菲咯啉（库珀，S.的R.;卡尔文，M. J. Am. Chem.Soc.1977，99，6623-6630）和线性单-μ-氧代化合物[LMn（III）OMn（III）L]（ClO 4）2，其中L-是单阴离子N，N-双（2-吡啶基甲基）-N’-亚水杨基-1，2-二氨基乙烷配体（Horner，O.; Anxolabéhère-Mallart，E.; Charlot，M. F.地; Tchertanov，L.; Guilhem，J.; Mattioli，T.一、Boussac，A.; Gired，J.- 1999，38，1222-1232）。在乙腈中的电解体被用来获得更高的氧化态的化合物：Mn（IV）Mn（IV）的二-mu-氧代化合物和Mn（III）Mn（IV）和Mn（IV）Mn（IV）物种的单-mu-氧代化合物。使用IR、UV/维斯、EPR和EXAFS光谱测定各种样品溶液的纯度和完整性。锰K-边XANES光谱转移到更高的能量氧化时，配体环境保持相似。然而，也观察到能量的变化时，只有配体环境被改变。这是通过比较等效氧化态的二-mu-氧代和线性单-mu-氧代Mn-Mn部分来实现的，这代表了主要的结构变化。由于配体环境的主要变化而引起的能量转移的幅度可以与氧化态变化的幅度一样大。因此，当将Mn K-边缘能量与锰氧化态相关联时，必须小心，而不考虑配体环境的性质和化合物的整体结构。与Mn K边XANES相比，Kbeta XES光谱对配体环境的依赖性较小。Kbeta 1，3峰能量是相当的二-mu-氧代和单-mu-氧代化合物在等效氧化态。由于氧化观察到的能量位移也是类似的两种不同的化合物。结合Kbeta XES的XANES前边缘和主边缘特征的不同行为的研究提供了关于锰原子的配体环境的氧化态和特征的重要信息。
Two structurally homologous Mn compounds in different oxidation states were studied to investigate the relative influence of oxidation state and ligand environment on Mn K-edge X-ray absorption near-edge structure (XANES) and Mn Kbeta X-ray emission spectroscopy (Kbeta XES). The two manganese compounds are the di-mu-oxo compound [L'2Mn(III)O2Mn(IV)L'2](ClO4)3, where L' is 1,10-phenanthroline (Cooper, S. R.; Calvin, M. J. Am. Chem. Soc. 1977, 99, 6623-6630) and the linear mono-mu-oxo compound [LMn(III)OMn(III)L](ClO4)2, where L- is the monoanionic N,N-bis(2-pyridylmethyl)-N'-salicylidene-1,2-diaminoethane ligand (Horner, O.; Anxolabéhère-Mallart, E.; Charlot, M. F.; Tchertanov, L.; Guilhem, J.; Mattioli, T. A.; Boussac, A.; Girerd, J.-J. Inorg. Chem. 1999, 38, 1222-1232). Preparative bulk electrolysis in acetonitrile was used to obtain higher oxidation states of the compounds: the Mn(IV)Mn(IV) species for the di-mu-oxo compound and the Mn(III)Mn(IV) and Mn(IV)Mn(IV) species for the mono-mu-oxo compound. IR, UV/vis, EPR, and EXAFS spectra were used to determine the purity and integrity of the various sample solutions. The Mn K-edge XANES spectra shift to higher energy upon oxidation when the ligand environment remains similar. However, shifts in energy are also observed when only the ligand environment is altered. This is achieved by comparing the di-mu-oxo and linear mono-mu-oxo Mn-Mn moieties in equivalent oxidation states, which represent major structural changes. The magnitude of an energy shift due to major changes in ligand environment can be as large as that of an oxidation-state change. Therefore, care must be exercised when correlating the Mn K-edge energies to manganese oxidation states without taking into account the nature of the ligand environment and the overall structure of the compound. In contrast to Mn K-edge XANES, Kbeta XES spectra show less dependence on ligand environment. The Kbeta1,3 peak energies are comparable for the di-mu-oxo and mono-mu-oxo compounds in equivalent oxidation states. The energy shifts observed due to oxidation are also similar for the two different compounds. The study of the different behavior of the XANES pre-edge and main-edge features in conjunction with Kbeta XES provides significant information about the oxidation state and character of the ligand environment of manganese atoms.