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首页> 外文期刊>Chemistry: A European journal >Bonding Characteristics Mediated by Saddle-Shaped Porphyrin Deformation: A Theoretical Approach to the Control of Spin State of Iron (III) Porphyrins
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Bonding Characteristics Mediated by Saddle-Shaped Porphyrin Deformation: A Theoretical Approach to the Control of Spin State of Iron (III) Porphyrins

机译：鞍形卟啉变形介导的键合特性：铁（III）卟啉自旋态控制的理论方法

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摘要

Five-coordinate iron (III) porphyrin complexes can exist in high-spin (S=5/2), intermediate-spin (S=3/2), and admixed intermediate-spin (S=5/2, 3/2) states. It has been found that weak-field axial ligands, a small core size of porphyrin macrocycle, and saddleshaped deformation of porphyrin macrocycle induces the contribution of intermediate spin to the ground state. While the experimental ground state depends on the nature of axial ligands and porphyrin macrocycles, EHT and INDO calculations on a series of five-coordinate iron (III) porphyrin complexes in this study suggest a clear crystal-field explanation of the factors that can contribute to the stability of the intermediate-spin state. Based on our calculations, all these factors can increase the energy separation between the d_(x~2-y~2)and d_(z~2) orbitals and between the d_(x~2-y~2) and d_(xy) orbitals and contribute to the relative stability of intermediate-spin state. Saddle-shaped deformation of porphyrin decreases the symmetry (C_(4v) -> (C_(2v)) of the coordination sphere and increases the probabilities of bonding interactions between metal and macrocycle. It is the number of bonding interactions of saddle-shaped metalloporphyrins that elevates the energy of d_(x~2-y~2) orbital. On the other hand, for the same symmetry rationalization, d_(x~2-y~2) and d_(z~2) orbitals are extensively hybridized and induce large electronic structure asymmetry to the saddle-shaped iron (III) porphyrin complexes. A novel concept of symmetry switch to control the spin transfer pathway that may be critical to the biological activities in nature is proposed.
机译：五配位铁（III）卟啉配合物可存在于高旋转（S = 5/2），中旋转（S = 3/2）和混合的中旋转（S = 5 / 2、3 / 2）中状态。已经发现，弱场轴向配体，卟啉大环的小核尺寸和卟啉大环的鞍形变形引起中间自旋对基态的贡献。尽管实验的基态取决于轴向配体和卟啉大环的性质，但在这项研究中对一系列五配位铁（III）卟啉配合物的EHT和INDO计算表明，晶格场解释了可能导致该现象的因素中间自旋状态的稳定性。根据我们的计算，所有这些因素都可以增加d_（x〜2-y〜2）和d_（z〜2）轨道之间以及d_（x〜2-y〜2）和d_（xy ）轨道并有助于中间自旋状态的相对稳定性。卟啉的鞍形变形降低了配位体的对称性（C_（4v）->（C_（2v）），增加了金属与大环之间键合相互作用的概率，即鞍形金属卟啉键合相互作用的数量。另一方面，对于相同的对称性合理化，d_（x〜2-y〜2）和d_（z〜2）轨道被广泛地杂交，从而提高了d_（x〜2-y〜2）轨道的能量。诱导鞍形铁（III）卟啉配合物具有较大的电子结构不对称性，提出了一种新的对称开关概念，以控制自旋转移途径，这可能对自然界的生物活性至关重要。

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