Chen Yinjuan, Jin Jiaye, Xin Ke, Yu Wenjie, Xing Xiaopeng, Wang Xuefeng, Wang Guanjun
School of Chemical Science and Engineering, Shanghai Key Lab of Chemical Assessment and Sustainability, Tongji University, 1239 Siping Road, Shanghai, 200092, China.
Department of Chemistry, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University, 2005 Songhu Road, Shanghai 200438, China.
Phys Chem Chem Phys. 2019 Jul 17;21(28):15639-15646. doi: 10.1039/c9cp02171j.
We investigate the gaseous ScO(H2O)1-3Ar+ cations prepared by laser vaporization coupled with supersonic molecular beam using infrared photodissociation spectroscopy in the O-H stretching region. The cation structures are characterized by comparing the experimentally observed frequencies with the simulated vibration spectra. We reveal that stoichiometric ScO(H2O)Ar+ is intrinsically the hydrated oxide cation expressed as H2O-ScOAr+ hydrate rather than Sc(OH)2Ar+ dihydroxide, although the former is higher in energy by 29.5 kcal mol-1 than the latter. Interestingly, when more water molecules are introduced to the complex, we find that the stoichiometric ScO(H2O)2-3Ar+ embraces the core subunit of Sc(OH)2+. Theoretical calculations suggest that the energy barrier of hydrogen transfer plays a critical role in the isomerization from hydrated complex to dihydroxide. When more than one water molecule is involved in the complex, the hydrogen transfer becomes nearly barrierless through a six-member cyclic transition state, leading to the reduction in the energy barrier from 21.8 kcal mol-1 to 4.2 kcal mol-1. Altogether, we conclude that the solvent molecules such as water can decrease the energy barrier and thus induce the formation of hydroxy species in the hydrolysis process.
我们利用红外光解离光谱，在O-H伸缩区域研究了通过激光蒸发与超声分子束相结合制备的气态ScO(H₂O)₁₋₃Ar⁺阳离子。通过将实验观测频率与模拟振动光谱进行比较，对阳离子结构进行了表征。我们发现化学计量比的ScO(H₂O)Ar⁺本质上是表示为H₂O-ScOAr⁺水合物的水合氧化物阳离子，而不是Sc(OH)₂Ar⁺二氢氧化物，尽管前者的能量比后者高29.5千卡/摩尔。有趣的是，当向络合物中引入更多水分子时，我们发现化学计量比的ScO(H₂O)₂₋₃Ar⁺包含Sc(OH)₂⁺的核心亚基。理论计算表明，氢转移的能垒在从水合络合物到二氢氧化物的异构化过程中起关键作用。当络合物中涉及多个水分子时，通过六元环状过渡态，氢转移几乎没有能垒，导致能垒从21.8千卡/摩尔降低到4.2千卡/摩尔。总之，我们得出结论，诸如水之类的溶剂分子可以降低能垒，从而在水解过程中诱导羟基物种的形成。
