Oudsen J P H, Venderbosch B, Korstanje T J, Tromp M
Sustainable Materials Characterization, Van't Hoff Institute for Molecular Sciences, University of Amsterdam Science Park 904 1098 XH Amsterdam The Netherlands.
Materials Chemistry, Zernike Institute for Advanced Materials Nijenborgh 4 9747AG Groningen The Netherlands
RSC Adv. 2020 Jan 2;10(2):729-738. doi: 10.1039/c9ra08903a.
Di-iron dithiolate hydrogenase model complexes are promising systems for electrocatalytic production of dihydrogen and have therefore been spectroscopically and theoretically investigated in this study. The direct effect of ligand substitution on the redox activity of the complex is examined. In order to understand and eventually optimize such systems, we characterised both metal and ligand in detail, using element specific X-ray absorption Fe- and S-K edge XAS. The (electronic) structure of three different [FeS] hydrogenase systems in their non-reduced state was investigated. The effect of one- and two-electron reduction on the (electronic) structure was subsequently investigated. The S K-edge XAS spectra proved to be sensitive to delocalization of the electron density into the aromatic ring. The earlier postulated charge and spin localization in these complexes could now be measured directly using XANES. Moreover, the electron density (from S K-edge XANES) could be directly correlated to the Fe-CO bond length (from Fe K-edge EXAFS), which are in turn both related to the reported catalytic activity of these complexes. The delocalization of the electron density into the conjugated π-system of the aromatic moieties lowers the basicity of the diiron core and since protonation occurs at the diiron (as a rate determining step), lowering the basicity decreases the extent of protonation and consequently the catalytic activity.
二铁二硫醇脱氢酶模型配合物是用于电催化生产氢气的有前景的体系，因此在本研究中对其进行了光谱和理论研究。研究了配体取代对配合物氧化还原活性的直接影响。为了理解并最终优化此类体系，我们使用元素特异性X射线吸收Fe和S-K边XAS对金属和配体进行了详细表征。研究了三种不同的[FeS]氢化酶体系在非还原状态下的（电子）结构。随后研究了单电子和双电子还原对（电子）结构的影响。S K边XAS光谱被证明对电子密度离域到芳环中敏感。现在可以使用XANES直接测量这些配合物中早期假设的电荷和自旋定位。此外，（来自S K边XANES的）电子密度可以直接与（来自Fe K边EXAFS的）Fe-CO键长相关，而这两者又都与这些配合物报道的催化活性相关。电子密度离域到芳族部分的共轭π体系中会降低二铁核心的碱性，并且由于质子化发生在二铁处（作为速率决定步骤），降低碱性会降低质子化程度，从而降低催化活性。
