Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun 130024, PR China.
Dalton Trans. 2013 Aug 7;42(29):10617-25. doi: 10.1039/c3dt50666e. Epub 2013 Jun 13.
Water oxidation is a key half reaction in the energy conversion scheme. The reaction mechanism for the oxidation of H2O to O2 catalyzed by single-Ru-substituted polyoxometalates, Ru(III)(H2O)XW11O39 (X = Si(IV), Ge(IV)), was investigated by means of density functional calculations. The electronic structure of the pre-activation intermediates indicates that the aqua ligand is prone to accommodate the proton coupled electron transfer (PCET) process to achieve the active group [Ru(V)=Oa], and the high valent oxo-ruthenium(V) species are responsible for the O-O forming event. Three possible proton acceptors were designed for the rate-determining step (Ob, Oa, and H2O), the calculated results support that the bridge Ob atom of the polytungstate ligand will act as the most favorable proton acceptor in the O-O bond formation, with an energy barrier of 28.43 kcal mol(-1). A detailed information of the peroxidic intermediates in the oxidation process was also characterized, both the peroxo-species Ru(IV)(OO)SiW11O39 and Ru(V)(OO)SiW11O39 show the six-coordinate isomer with an open terminal geometry is more favorable than the close seven-coordinate ones. In addition, the replacement of the heteroatom in XO4(n-) can effectively tune the catalytic activity of polyoxometalates, in the order of Ge(IV) > Si(IV).
水氧化是能量转换方案中的关键半反应。通过密度泛函计算研究了单 Ru 取代多金属氧酸盐Ru(III)(H2O)XW11O39（X = Si(IV)，Ge(IV)）催化 H2O 氧化为 O2 的反应机理。预活化中间体的电子结构表明，水合配体易于容纳质子耦合电子转移（PCET）过程，以实现活性基团[Ru(V)=Oa]，高价氧代钌（V）物种负责 O-O 形成事件。为速率决定步骤（Ob、Oa 和 H2O）设计了三个可能的质子受体，计算结果支持多钨配体的桥 Ob 原子将作为 O-O 键形成中最有利的质子受体，能垒为 28.43 kcal mol(-1)。还对氧化过程中过氧中间体的详细信息进行了表征，过氧物种Ru(IV)(OO)SiW11O39和Ru(V)(OO)SiW11O39均显示出具有开放端立体化学的六配位异构体比封闭的七配位异构体更有利。此外，XO4(n-)中杂原子的取代可以有效地调节多金属氧酸盐的催化活性，顺序为 Ge(IV) > Si(IV)。
