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首页> 外文期刊>Inorganic Chemistry: A Research Journal that Includes Bioinorganic, Catalytic, Organometallic, Solid-State, and Synthetic Chemistry and Reaction Dynamics >Spectroscopy of Non-Heme Iron Thiolate Complexes:Insight into the Electronic Structure of the Low-Spin Active Site of Nitrile Hydratase
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Spectroscopy of Non-Heme Iron Thiolate Complexes:Insight into the Electronic Structure of the Low-Spin Active Site of Nitrile Hydratase

机译：非血红素硫氰酸铁络合物的光谱学：对腈水合酶低旋转活性位的电子结构的了解

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Detailed spectroscopic and computational studies of the low-spin iron complexes [Fe~(lll)(S_2~(Me2)N_3(Pr,Pr))(N_3)] (1) and [Fe~(lll)(S_2~(Me2)N_3(Pr,Pr))]~(1+) (2) were performed to investigate the unique electronic features of these species and their relation to the low-spin ferric active sites of nitrile hydratases.Low-temperature UV/vis/NIR and MCD spectra of 1 and 2 reflect electronic structures that are dominated by antibonding interactions of the Fe 3d manifold and the equatorial thiolate S 3p orbitals.The six-coordinate complex 1 exhibits a low-energy S_pi-> Fe 3d_(xy) (~13000 cm~(-1) charge-transfer transition that results predominantly from the low energy of the singly occupied Fe 3d_(xy) orbital,due to pure pi interactions between this acceptor orbital and both thiolate donor ligands in the equatorial plane.The 3d_(pi) -> 3d_(sigma) ligand-field transitions in this species occur at higher energies (>15000 cm~(-1)),reflecting its near-octahedral symmetry.The Fe 3d_(xz,yz) -> Fe 3d_(xy) (d_pi -> d_pi) transition occurs in the near-IR and probes the Fe~(III)-S pi-donor bond;this transition reveals vibronic structure that reflects the strength of this bond (v_e approx = 340 cm~(-1)).In contrast,the ligand-field transitions of the five-coordinate complex 2 are generally at low energy,and the S_pi-> Fe charge-transfer transitions occur at much higher energies relative to those in 1.This reflects changes in thiolate bonding in the equatorial plane involving the Fe 3d_(xy) and Fe 3d_(x~2-y~2 orbitals.The spectroscopic data lead to a simple bonding model that focuses on the a and pi interactions between the ferric ion and the equatorial thiolate ligands,which depend on the S-Fe-S bond angle in each of the complexes.These electronic descriptions provide insight into the unusual S = 1/2 ground spin state of these complexes:the orientation of the thiolate ligands in these complexes restricts their pi-donor interactions to the equatorial plane and enforces a low-spin state.These anisotropic orbital considerations provide some intriguing insights into the possible electronic interactions at the active site of nitrile hydratases and form the foundation for further studies into these low-spin ferric enzymes.
机译：低自旋铁络合物[Fe〜（III）（S_2〜（Me2）N_3（Pr，Pr））（N_3）]（1）和[Fe〜（III）（S_2〜（Me2）的详细光谱和计算研究）N_3（Pr，Pr））]〜（1+）（2）用于研究这些物种的独特电子特征以及它们与腈水合酶的低旋铁活性位点的关系。 1和2的NIR和MCD光谱反映了以Fe 3d流形与赤道硫醇盐S 3p轨道的反键相互作用为主的电子结构。六坐标复合物1表现出低能S_pi-> Fe 3d_（xy）（ 〜13000 cm〜（-1）的电荷转移跃迁，主要是由于单个受体的Fe 3d_（xy）轨道的低能所致，这是由于该受体轨道与赤道平面中两个硫醇盐供体配体之间存在纯pi相互作用。该物种的3d_（pi）-> 3d_sigma配体场跃迁发生在较高能量（> 15000 cm〜（-1））处，反映了其接近八面体的对称性.Fe 3d_（xz，yz）-> Fe 3d_（xy）（d_pi-> d_pi）跃迁在近红外中发生并探测Fe〜（III）-S pi供体键;该跃迁揭示了反映该键强度的振动电子结构（v_e大约= 340 cm〜（-1））。相反，五配位配合物2的配体场跃迁通常处于低能状态，而S_pi-> Fe电荷转移跃迁发生的能量远高于1中的那些。这反映了涉及Fe 3d_（xy）和Fe 3d_（x〜2-y〜2轨道）的赤道面硫醇盐键的变化。光谱数据导致了一个简单的键合模型，该模型专注于三价铁之间的a和pi相互作用离子和赤道硫醇盐配体，这取决于每个配合物中的S-Fe-S键角。这些电子描述提供了洞察这些配合物异常S = 1/2的自旋态：硫醇盐配体的取向在这些复合体中，它们的π-供体相互作用限制在赤道平面上，并强制低速旋转这些各向异性的轨道考虑因素为腈水合酶活性位点可能发生的电子相互作用提供了一些有趣的见解，并为进一步研究这些低旋铁酶奠定了基础。

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