四苯基铁卟啉双氧加合物的密度泛函理论研究

采用密度泛函理论方法计算了自旋多重度为1、3、5的四苯基铁卟啉双氧加合物(FeTPPO2)的几何构型及电子性质。考察了四苯基铁卟啉对分子氧的活化。研究发现,FeTPPO2能量随自旋多重度升高而降低。五重态FeTPPO2的能量最低,但其铁卟啉对分子氧的活化效果最差。FeTPPO2中Oa—Ob键键长随自旋多重度变化的规律为三重态>单重态>五重态,说明三重态FeTPPO2中分子氧活化最明显。Fe—Oa键键长和Oa—Ob键键长呈负相关关系。电荷布居分析表明,FeTPPO2中分子氧活化程度与分子氧上所带负电荷多少有关,所带负电荷越多,分子氧活化越明显。分析自旋密度得知,三重态FeTPPO2中分子氧为单线态分子氧。三重态和五重态FeTPPO2中,铁离子均向分子氧转移了β电子,有利于铁氧键的形成。

A DFT Investigation on the Dioxygen Adduct of Iron Tetraphenylporphyrin

The singlet,triplet and quintet dioxygen adducts of the iron tetraphenylporphyrin(FeTPPO2) were investigated at B3LYP/6-31G* level using Gaussian09 program package without any symmetry constraint.It is found that the total energy of FeTPPO2 is reduced with the spin multiplicity increasing.The iron tetraphenylporphyrin in the quintet FeTPPO2 has little effect on activating dioxygen,although the quintet is the most stable spin state for FeTPPO2.The Fe—Oa bond length in FeTPPO2 is changed in the sequence of the tripletthe singlet>the quintet.It is shown that the activation of dioxygen in the triplet FeTPPO2 is most significant.There is a negative correlation between the Fe—Oa bond length and Oa—Ob bond length caused by the feedback bond from Fe 3d orbitals to the dioxygen of π* orbital and the ionic bond between Fe and Oa.Charge population analysis reveals that the dioxygen in FeTPPO2 always carries negative charges owing to the feedback bond from Fe 3d orbitals to the dioxygen of π* orbital.The activation of dioxygen in FeTPPO2 has to do with the negative charge carried by dioxygen,that is,the more negative charges dioxygen bears,the more significant the activation of dioxygen is.According to the spin density,the dioxygen in the triplet FeTPPO2 is in an excited singlet,so the triplet FeTPPO2 may be more chemically active than the quintet FeTPPO2.β electrons are transferred to the dioxygen from the central iron ion in both triplet and quintet FeTPPO2,which is favorable for the formation of Fe—Oa bond.