Does one hydrogen atom matter? Crystal structures and spectroscopic studies of five-coordinate manganese porphyrin complexes
Does one hydrogen atom matter? Crystal structures and spectroscopic studies of five-coordinate manganese porphyrin complexes
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DOI：
10.1016/j.dyepig.2022.111068
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发表时间：
2023-01-03
影响因子：
4.5
通讯作者：
Li，Jianfeng
中科院分区：
文献类型：
--
作者：
Liang，Xu;Zhao，Jianping;Li，Jianfeng
金属卟啉和咪唑（ate）长期以来一直被用来模拟金属酶，如五配位血红素配合物。本工作以2-甲基咪唑（2-MeHIm）或2-甲基咪唑（2-MeIm）为轴向配体，合成了几种五配位锰卟啉配合物，并通过单晶X射线、紫外可见、密度泛函和电子顺磁共振（EPR）等方法对其结构进行了表征，探讨了它们的几何结构和电子结构。紫外-可见光谱和晶体结构研究均显示两种物质之间存在显著差异（例如，2-MeIm衍生物的不寻常Soret带分裂），这与2-甲基咪唑酯的更强配体性质一致。对所有产物的固态和溶液态进行了低温（4K）EPR测量，给出了高自旋（S = 5/2）d_5体系的特征信号，g_（？）= 5.9，g_（？）= 2.0。值得注意的是，λ（E/D）和超精细分裂的数量之间的正相关性通过双重测量得到证实，例如[Mn（TPP）（2-MeHIm）]比[Mn（TMP）（2-MeIm）]多两个超精细分裂，λ更大（0.018 vs. 0.002）。
Metalloporphyrins and imidazole(ate) have long been employed to mimic metalloenzymes such as five-coordinate heme complexes. In this work, several five-coordinate manganese(II) porphyrin complexes utilizing sterically hindered 2-methylimidazole (2-MeHIm) or 2-methylimidazolate (2-MeIm‾) as axial ligand are isolated and characterized by single-crystal X-ray, UV–vis, DFT and electronic paramagnetic resonance (EPR) spectroscopies to explore their geometric and electronic structures. Both UV–vis and crystal structural investigations revealed noteworthy differences between the two species (e.g. the unusual Soret band split of 2-MeIm‾ derivatives) which are consistent with the stronger ligand nature of 2-methylimidazolate. Low temperature (4 K) EPR measurements have been carried out for all the products in both solid and solution states which gave characteristic signals of a high-spin (S = 5/2) d5system with g⊥ ≈ 5.9 and g// ≈ 2.0. Notably, the positive correlation between λ (E/D) and the numbers of hyperfine splittings are confirmed by double measurements e.g. [Mn(TPP)(2-MeHIm)] exhibits two more hyperfine splittings than [Mn(TMP)(2-MeIm‾)]‾ with a larger λ (0.018 vs. 0.002).