Molecular and electronic structures of mononuclear iron complexes using strongly electron-donating ligands and their oxidized forms.
Molecular and electronic structures of mononuclear iron complexes using strongly electron-donating ligands and their oxidized forms.
复制标题
使用强给电子配体及其氧化形式的单核铁配合物的分子和电子结构。
DOI：
10.1021/ic800335t
复制
发表时间：
2008
影响因子：
4.6
通讯作者：
Glaser,Thorsten
中科院分区：
文献类型：
--
作者：
Strautmann,JuliaBH;George,SerenaDeBeer;Bothe,Eberhard;Bill,Eckhard;Weyhermuller,Thomas;Stammler,Anja;Bogge,Hartmut;Glaser,Thorsten
配体L2 −（H2L = N，N ′-二甲基-N，N ′-双（3，5-二叔丁基-2-羟基苄基）-1，2-二氨基乙烷）已被用于合成两个单核Fe III配合物，即[LFe（η 2-NO3）]和[LFeCl]。L2 −是由四个强供电子基团（两个叔胺和两个酚盐）组成，它们增加了配位铁离子的电子密度。该性质应促进络合物的氧化，即氧化物质的稳定化。通过X射线衍射研究确定了固态分子结构。[LFeCl]为五配位的四方锥配位环境，配体为反式构象;[LFe（η 2-NO3）]为六配位的畸变八面体配位环境，配体为β-顺式构象。电子结构已经用磁化强度、EPR、Mo穆斯堡尔谱（有和没有外加场）、UV − vis − NIR和X射线吸收光谱进行了研究，证明了强σ和π供体酚盐的高度各向异性共价性。该分析得到[LFeCl]的DFT计算的支持。已被用来获得洞察在溶液中的两个配合物的分子结构中的变化，以及理解的光谱数据在固态的光谱数据在溶液中。虽然在非极性非质子溶剂的溶液中保留了固态的分子结构，但是在所有质子极性溶剂中存在一种共同的分子结构。LMCT跃迁和菱形E/D的分析清楚地表明，这两种化合物在这些质子极性溶剂中表现出β-顺式构象。这两个开放的配位位点，彼此顺式，允许两个潜在的配体接近。电化学分析确定了[LFeCl]在+0.55 V和+0.93 V（相对于Fc +/Fc）处的两个可逆氧化波，以及[LFe（η 2-NO3）]在+0.59 V处的一个可逆氧化波和在+1.07 V（相对于Fc +/Fc）处的不可逆氧化波。用计时电流法研究了[LFeCl]的单电子和双电子氧化反应。中心在420 nm处的强带的增加表明[LFeCl]+作为FeIIImonophenoxyl自由基络合物和[LFeCl] 2+作为FeIIIbisphenoxyl自由基络合物的制剂。这些研究意味着配体L2 −能够提供灵活的配位几何结构，具有两个底物结合位点和配体上两个氧化当量的分配。
The ligand L2−(H2L =N,N′-dimethyl-N,N′-bis(3,5-di-t-butyl-2-hydroxybenzyl)-1,2-diaminoethane) has been employed for the synthesis of two mononuclear FeIIIcomplexes, namely, [LFe(η2-NO3)] and [LFeCl]. L2−is comprised of four strongly electron-donating groups (twotert-amines and two phenolates) that increase the electron density at the coordinated ferric ions. This property should facilitate oxidation of the complexes, that is, stabilization of the oxidized species. The molecular structures in the solid state have been established by X-ray diffraction studies. [LFeCl] is five-coordinate in a square-pyramidal coordination environment with the ligand adopting atrans-conformation, while [LFe(η2-NO3)] is six-coordinate in a distorted octahedral environment with the ligand in a β-cis conformation. The electronic structures have been studied using magnetization, EPR, Mössbauer (with and without applied field), UV−vis−NIR, and X-ray absorption spectroscopies, which demonstrate highly anisotropic covalency from the strong σ- and π-donating phenolates. This analysis is supported by DFT calculations on [LFeCl]. The variations of the well-understood spectroscopic data in the solid state to the spectroscopic data in solution have been used to obtain insight in the molecular structure of the two complexes in solution. While the molecular structures of the solid states are retained in solutions of nonpolar aprotic solvents, there is, however, one common molecular structure in all protic polar solvents. The analysis of the LMCT transitions and the rhombicityE/Dclearly establish that both compounds exhibit a β-cis conformation in these protic polar solvents. These two open coordination sites, cis to each other, allow access for two potential ligands in close proximity. Electrochemical analysis establishes two reversible oxidation waves for [LFeCl] at +0.55 V and +0.93 V vs Fc+/Fc and one reversible oxidation wave at +0.59 V with an irreversible oxidation at +1.07 V vs Fc+/Fc for [LFe(η2-NO3)]. The one- and the two-electron oxidations of [LFeCl] by chronoamperometry have been followed spectroscopically. The increase of a strong band centered at 420 nm indicates the formulation of [LFeCl]+as a FeIIImonophenoxyl radical complex and of [LFeCl]2+as a FeIIIbisphenoxyl radical complex. These studies imply that the ligand L2−is capable of providing a flexible coordination geometry with two binding sites for substrates and the allocation of two oxidation equivalents on the ligand.