M(EDTA)2－ (M＝Co, Ni, Cu, Zn, Cd)电子结构和性质的密度泛函理论研究

在B3LYP/LanL2DZ水平上, 计算研究了Co^2＋, Ni^2＋, Cu^2＋, Zn^2＋, Cd^2＋与乙二胺四乙酸(EDTA)六配位模式下配合物的结构和性质. 除Cu(EDTA)^2－的M—O(5)受Jahn-Teller效应影响明显拉长外, 配位键长M—N(1)和M—O(5)按 Cu^2＋＜Ni^2＋＜Co^2＋＜Zn^2＋＜Cd^2＋的顺序依次增长, 配位键长M—O(3)按Cu^2＋＜Zn^2＋＜Ni^2＋＜Co^2＋＜Cd^2＋的次序依次增长. 自然键轨道(NBO)分析表明, 氮、氧的非键电子与金属空轨道的相互作用是配体与金属离子配位的主要作用方式. 通过对N(1)—C(7), N(1)—C(9), N(1)—C(15)键长和NAO键级的分析, 在分子水平上阐明了EDTA在与金属离子配位前后发生首步降解, 其产物存在差异的实验事实. 依据热力学原理并兼顾自洽反应场(SCRF)的IEFPCM模型, 我们设计了金属离子与EDTA在水溶液中的反应途径和热力学循环. 结果表明, 金属离子与EDTA的结合能(即配位稳定性)依次为: Cd^2＋＜Zn^2＋＜Co^2＋＜Ni^2＋＜Cu^2＋, 金属离子的水合吉布斯自由能计算值与实验值大致吻合, 而且上述目标金属配合物的络合吉布斯自由能的递变规律与实验一致. 基于气相优化结构进行了振动频率计算, 并对部分重要的振动峰作了归属指认. 结果表明, 随着配位稳定性的减弱, M(EDTA)^2－具有红外活性的金属敏感性振动峰ν(M—N)和ν(M—O)的峰位依次红移.

A Density Functional Theory Study on the Electronic Structures and Properties of Methylenediaminetetraacetate Complexes (M=Co, Ni, Cu, Zn, Cd)

The structures and properties of the octahedral M-ethylenediaminetetraacetate complexes (M＝Co^2＋, Ni^2＋, Cu^2＋, Zn^2＋, Cd^2＋) have been studied using density functional theory method at the B3LYP/LanL2DZ level. Apart from the M—O(5) of Cu(EDTA)^2－ which is obviously elongated because of Jahn-Teller effect, the bond lengths of M—N(1) and M—O(5) are increased gradually in the order of Cu^2＋＜Ni^2＋＜Co^2＋＜Zn^2＋＜Cd^2＋while the bond lengths of M—O(3) are increased in the order of Cu^2＋＜Zn^2＋＜Ni^2＋＜Co^2＋＜Cd^2＋. The NBO analysis shows that the interaction between the non-bonded electrons of nitrogen and oxygen atoms and the vacant orbitals of metals is vital for the complexation. Based on the analysis of bond lengths and NAO bond orders of N(1)—C(7), N(1)—C(9) and N(1)—C(15), the fact that the complexed and uncomplexed EDTA turn out different products in the degradation process is illustrated on the level of molecule. According to the thermodynamic theory with considering the IEFPCM model of self-consistent reaction field (SCRF) as well, we have designed reactions and a thermodynamic cycle for the hydrate metal ions and EDTA in aqueous solution. The energetic results indicate that the sequence of binding energies of cations and EDTA (i.e. complexation stability) is Cd^2＋＜Zn^2＋＜Co^2＋＜Ni^2＋＜Cu^2＋. The calculated Gibbs free energies of hydration for metal ions are in agreement with their experimental values as well as the order of complexation Gibbs free energies of studied complexes. Based on the vibrational analysis upon the optimized geometry in gas phase, some important peaks of the infrared spectra are assigned. The IR result shows that the ν(M—N) and ν(M—O), the IR activitied metal sensitive vibrations of M(EDTA)^2－ complexes, are shifted towards higher along with increase of complexation stability.