钒取代α-Keggin型杂多阴离子簇合物[PVnMo(12-n)O(40)]^(3＋n)^-(n=1～3)氧化性能的DFT研究

DFT Study on the Oxidative Property of Vanadium(V)-substituted α-Keggin-type Heteropolyanion Clusters [PV_nMo_(12-n)O_(40)]^((3+n)-)(n=1～3)

运用密度泛函理论的离散变分(DFT-DVM)方法,通过理论计算和模拟,将不同个数V取代的α-Keggin型磷钼杂多阴离子簇合物以及它们的各个异构体区分开来,探讨了V的取代效应对所形成物种[PVnMo12-nO40](3+n)-(n=1～3)的氧化活性的影响.研究表明,单钒取代的簇阴离子的氧化活性最高,其次是二钒取代的物种,三钒取代的物种活性最低.将计算得到的结果与实验测得的还原电势进行关联后发现,这些杂多阴离子簇合物的费米能级(Ef)与其第一还原电势(ERP)之间呈现反比变化,随着V取代个数n的增加,簇阴离子所带的负电荷数逐渐增大,Ef值也随之增大,而相应物种的ERP却逐渐减小.进一步对含钨杂多阴离子簇合物[XW12O40]n-(X=CoII,FeIII,SiIV,PV)的计算分析证实,这种关系具有一定的普适性;在此基础上推测了杂多阴离子新物种[SW12O40]2-的存在,并预测了其可能具有的氧化活性.

Based on the density functional theory coupled with a discrete variational method （DFT-DVM）, several vanadium-substituted a-Keggin-type heteropolyanion phosphomolybadate clusters [PVnMo12-nO40]^（3＋n）- （n=1-3） and their isomers were modeled. The effects of the vanadium-substitution on the oxidative property of the title species were investigated. The results showed that, the oxidative activity of the mono-vanadium-substituted cluster was the highest among the title species, while the oxidative activities of the di- and tri-vanadium-substituted clusters lied behind, with the former more active than the latter. Combining the calculated results with the available experimental electron reduction potential （ERP） data, it was found that the Fermi energy levels （Ef） of these species changed inversely with their ERP data, that is, the Ef gets higher with increasing the substituted vanadium number （n） of vanadium atoms, the corresponding ERP gets smaller. Further calculations on the tungsten heteropolyanion clusters as the a-Keggin-type [XW12/O40]^n- （X=Co^Ⅱ, Fe^Ⅲ, si^Ⅳ, p^Ⅴ） also showed the same relationship of Ef with ERP. Based on theoretical calculations, the new a-Keggin heteropolyanion species [SW12O40]^2- was predicted and its Ef value was the smallest one among the tungsten heteropolyanion clusters, thus, it may possess cluster series [XW12O40]^n- （X=Co^Ⅱ, Fe^Ⅲ, Si^Ⅳ, p^Ⅴ, s^Ⅵ）.