Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4J3.
J Phys Chem A. 2010 Sep 23;114(37):10315-9. doi: 10.1021/jp105842k.
The displacement of the iron(II) atom from the porphyrin plane in iron(II) porphyrin complexes is investigated with respect to the spin state of iron(II) employing density functional theory. In this study the quantum theory of atoms in molecules (QTAIM) is used to show that the atomic volume of iron is smaller in the quintet state of imidazolium ligated iron(II) porphyrin than in the triplet state. This is consistent with what has been found for free atoms and contradicts the original interpretation of structural studies with X-rays, which assumed that the out-of-plane displacement of iron from the porphyrin ring in the quintet state is due to the increased spatial size of the high-spin iron atom. The bonding environment of the iron atom is analyzed with respect to the electron density (ρ) at the bond critical points (BCPs). It is found that in the quintet state, relative to the triplet state, there is a stronger bonding interaction between iron and the nitrogen atoms of the porphyrin despite a longer bond length. It has previously been suggested that the weakening of these bonds is the cause of the out-of-plane displacement of iron. Since this is not the case, this implies that the magnitude of the bonding interaction between the iron atom and the axial ligand has a more significant role in the domed structure of the quintet state.
采用密度泛函理论研究了铁(II)卟啉配合物中，铁原子从卟啉平面的位移与铁(II)自旋态的关系。在本研究中，我们使用分子中原子的量子理论（QTAIM）来表明，在咪唑配体铁(II)卟啉的五重态中，铁的原子体积小于三重态。这与自由原子的发现一致，与 X 射线结构研究的原始解释相矛盾，后者假设在五重态中，铁从卟啉环的面外位移是由于高自旋铁原子的空间尺寸增大。分析了铁原子的键合环境与键临界点（BCP）处的电子密度（ρ）之间的关系。结果表明，在五重态中，与三重态相比，尽管键长更长，但铁与卟啉氮原子之间的键合相互作用更强。先前曾有人提出，这些键的弱化是铁面外位移的原因。由于事实并非如此，这意味着铁原子与轴向配体之间的键合相互作用的大小对五重态的穹顶结构具有更重要的作用。
