Spectroscopic properties and electronic structure of five- and six-coordincate iron(II) porphyrin NO complexes:: Effect of the axial N-donor ligand
Spectroscopic properties and electronic structure of five- and six-coordincate iron(II) porphyrin NO complexes:: Effect of the axial N-donor ligand
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DOI：
10.1021/ic050865j
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发表时间：
2006-04-03
影响因子：
4.6
通讯作者：
Lehnert, N
中科院分区：
文献类型：
--
作者：
Praneeth, VKK;Näther, C;Lehnert, N
本文研究了[Fe（TPP）（NO）]（1; TPP =四苯基卟啉）和[Fe（TPP）（MI）（NO）]（2; MI = 1-甲基咪唑）型体系中五配位和六配位铁卟啉NO配合物的光谱性质和电子结构的差异。利用紫外-可见吸收光谱和核磁共振氢谱研究了轴向反式NO配体与1型五配位配合物的结合。首次确定了化合物1和2的结合常数K-eq，并对化合物1和2的H-1 NMR谱进行了归属。此外，H-1 NMR允许的程度的脱亚硝基化的解决方案中的I与过量的碱的测定。然后研究了轴向配体对配位NO性质的影响。振动光谱（IR和拉曼）的1和2，并分配使用同位素取代和正常坐标分析。得到的力常数为12.53（N-O）和2.98 mdyn/埃（Fe-NO）相比，1为11.55（N-O）和2.55 mdyn/埃（Fe-NO）2。与NMR结果一起，这提供了反式配体的结合减弱Fe-NO键的实验证据。1和2的主要成键方案非常相似。在这两种情况下，Fe-N-O亚基强烈弯曲。从NO的单占据π * 轨道到铁（II）的d（z2）的捐赠导致Fe-NO σ键的形成。此外，在这些配合物中存在中等强度的T背键。1和2的电子结构中最重要的差异发生在Fe-NO a键，这是明显更强的1与实验力常数一致。来自1中的NO的增加的σ捐赠也导致自旋密度从NO到铁的显著转移，如在先前的通信（Praneeth，V.K. K.的;尼塞; Lehnert，N. 2005，44，2570-2572）。这一点得到了H-NMR结果的证实。因此，提供了进一步的实验和计算证据，配合物1具有明显的（FeNO+）-N-1字符相对于2，这是一个（FeNO）-N-II（自由基）的配合物。最后，利用MCD理论和量子化学计算，首次对化合物1和2的吸收光谱和MCD C项光谱进行了归属。
In this paper, the differences in the spectroscopic properties and electronic structures of five- and six-coordinate iron(II) porphyrin NO complexes are explored using [Fe(TPP)(NO)] (1; TPP = tetraphenylporphyrin) and [Fe(TPP)(Ml)(NO)] (2; MI = 1-methylimidazole) type systems. Binding of N-donor ligands in axial position trans to NO to five-coordinate complexes of type 1 is investigated using UV-vis absorption and H-1 NMR spectroscopies. This way, the corresponding binding constants K-eq are determined and the H-1 NMR spectra of 1 and 2 are assigned for the first time. In addition, H-1 NMR allows for the determination of the degree of denitrosylation in solutions of I with excess base. The influence of the axial ligand on the properties of the coordinated NO is then investigated. Vibrational spectra (IR and Raman) of 1 and 2 are presented and assigned using isotope substitution and normal-coordinate analyses. Obtained force constants are 12.53 (N-O) and 2.98 mdyn/angstrom (Fe-NO) for 1 compared to 11.55 (N-O) and 2.55 mdyn/angstrom (Fe-NO) for 2. Together with the NMR results, this provides experimental evidence that binding of the trans ligand weakens the Fe-NO bond. The principal bonding schemes of 1 and 2 are very similar. In both cases, the Fe-N-O subunit is strongly bent. Donation from the singly occupied pi* orbital of NO into d(z2) of iron(II) leads to the formation of an Fe-NO sigma bond. In addition, a medium-strong,T back-bond is present in these complexes. The most important difference in the electronic structures of 1 and 2 occurs for the Fe-NO a bond, which is distinctively stronger for 1 in agreement with the experimental force constants. The increased sigma donation from NO in 1 also leads to a significant transfer of spin density from NO to iron, as has been shown by magnetic circular dichroism (MCD) spectroscopy in a preceding Communication (Praneeth, V. K. K.; Neese, F.; Lehnert, N. Inorg. Chem. 2005, 44, 2570-2572). This is confirmed by the H-1 NMR results presented here. Hence, further experimental and computational evidence is provided that complex 1 has noticeable (FeNO+)-N-1 character relative to 2, which is an (FeNO)-N-II(radical) complex. Finally, using MCD theory and quantum chemical calculations, the absorption and MCD C-term spectra of 1 and 2 are assigned for the first time.