High-frequency and -field electron paramagnetic resonance of high-spin manganese(III) in porphyrinic complexes
High-frequency and -field electron paramagnetic resonance of high-spin manganese(III) in porphyrinic complexes
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DOI：
10.1021/ic9901970
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发表时间：
1999-12-27
影响因子：
4.6
通讯作者：
Brunel, LC
中科院分区：
文献类型：
--
作者：
Krzystek, J;Telser, J;Brunel, LC
高场和频率电子顺磁共振（HFEPR）光谱已用于研究高自旋锰（III），d（4），S = 2的两种配合物。研究的配合物是（四苯基卟啉）氯化锰（III）和（酞菁）氯化锰（III）。我们之前的 HFEPR 研究（Goldberg, D. P.；Telser, J.；Krzystek, J.；Montalban, A. G.；Brunel, L.-C.；Barrett, A. G. M.；Hoffman, B. M. J. Ain. Chem. Sec. 1997, 119, 8722-8723）包括关于卟啉复合物的结果；然而，我们无法获得真正的粉末图案 HFEPR 光谱，因为微晶在强烈的外部磁场中定向。在这项工作中，我们现在能够将粉末固定在正二十烷研磨物或 KBr 颗粒中，并获得真实的粉末模式光谱。使用光谱模拟软件对这些光谱进行了全面分析，并为每个配合物确定了一套完整的自旋哈密顿参数。两种复合体都是严格的轴向系统，具有相对较低的零场分裂：D 接近-2.3 cm(-1)，g 值非常接近2.00。在此工作之前，对于卟啉配体的 Mn(III) 配合物中金属基电子能级，不存在任何实验或理论数据。与其他过渡金属配合物相比，这种信息的缺乏可能是由于此类 Mn(III) 配合物的吸收光谱中基于配体的过渡占主导地位。因此，我们利用了（酞菁）铜（II）的电子能级的理论值，它在电子上类似于这些Mn（III）络合物。从计算的 EPR 参数与实验确定的 EPR 参数之间的一致性来看，这种类比效果出人意料地好。这些结果表明，在具有卟啉配体的 Mn(III) 配合物中，三重态 (S = I) 激发态与五重态 (S = 2) 基态存在显着混合。这与其他金属卟啉配合物（例如 S = 1 的 Fe(II) 配合物）中较低自旋基态的实验观察结果一致。
High-field and -frequency electron paramagnetic resonance (HFEPR) spectroscopy has been used to study two complexes of high-spin manganese(III), d(4), S = 2. The complexes studied were (tetraphenylporphyrinato)manganese(III) chloride and (phthalocyanato)manganese(III) chloride. Our previous HFEPR study (Goldberg, D. P.; Telser, J.; Krzystek, J.; Montalban, A. G.; Brunel, L.-C.; Barrett, A. G. M.; Hoffman, B. M. J. Ain. Chem. Sec. 1997, 119, 8722-8723) included results on the porphyrin complex; however, we were unable to obtain true powder pattern HFEPR spectra, as the crystallites oriented in the intense external magnetic field. In this work we are now able to immobilize the powder, either in an n-eicosane mull or KBr pellet and obtain true powder pattern spectra. These spectra have been fully analyzed using spectral simulation software, and a complete set of spin Hamiltonian parameters has been determined for each complex. Both complexes are rigorously axial systems, with relatively low magnitude zero-field splitting: D approximate to -2.3 cm(-1) and g values quite close to 2.00. Prior to this work, no experimental nor theoretical data exist for the metal-based electronic energy levels in Mn(III) complexes of porphyrinic ligands. This lack of information is in contrast to other transition metal complexes and is likely due to the dominance of ligand-based transitions in the absorption spectra of Mn(III) complexes of this type. We have therefore made use of theoretical values for the electronic energy levels of (phthalocyanato)copper(II), which electronically resembles these Mn(III) complexes. This analogy works surprisingly well in terms of the agreement between the calculated and experimentally determined EPR parameters. These results show a significant mixing of the triplet (S = I) excited state with the quintet (S = 2) ground state in Mn(III) complexes with porphyrinic ligands. This is in agreement with the experimental observation of lower spin ground states in other metalloporphyrinic complexes, such as those of Fe(II) with S = 1.