Wang Dandan, Fujii Asuka
Department of Chemistry , Graduate School of Science , Tohoku University , Sendai 980-8578 , Japan . Email:
Chem Sci. 2017 Apr 1;8(4):2667-2670. doi: 10.1039/c6sc05361k. Epub 2017 Jan 11.
A two-center three-electron 2c-3e bond (hemi-bond) is a non-classical chemical bond, and its existence has been supposed in radical cation clusters with lone pairs. Though the nature of the hemi-bond and its role in the reactivity of radical cations have attracted great interest, spectroscopic observations of hemi-bonded structures have been very scarce. In the present study, the presence of a stable hemi-bonded core (HS∴SH) in (HS) ( = 3-6) in the gas phase is demonstrated by infrared spectroscopy combined with quantum chemical calculations. The spectral features of the free SH stretch of the ion core show that the hemi-bond motif of the ion core is maintained up to the completion of the first H-bonded solvation shell. All of the observed spectra are well reproduced by the minimum energy hemi-bonded isomers, and no sign of the proton-transferred ion core type HS-SH, which is estimated to have a much higher energy, is found. Spin density calculations show that the excess charge is almost equally delocalized over the two HS molecules in the cluster for = 3 to 6. This also indicates the hemi-bond nature of the (HS∴SH) ion core and the small impact of the formation of a solvation shell on the ion core.
双中心三电子2c-3e键（半键）是一种非经典化学键，其存在已在具有孤对电子的自由基阳离子簇中被推测。尽管半键的性质及其在自由基阳离子反应性中的作用引起了极大兴趣，但对半键合结构的光谱观测却非常稀少。在本研究中，通过红外光谱结合量子化学计算，证明了气相中(HS) ( = 3 - 6) 存在稳定的半键合核心（HS∴SH）。离子核心自由SH伸缩振动的光谱特征表明，离子核心的半键基序在第一个氢键溶剂化壳层形成完成之前一直保持。所有观测光谱都能被最低能量的半键合异构体很好地重现，并且未发现估计能量高得多的质子转移离子核心类型HS - SH的迹象。自旋密度计算表明，对于 = 3至6，簇中两个HS分子上的多余电荷几乎均匀离域。这也表明了(HS∴SH) 离子核心的半键性质以及溶剂化壳层形成对离子核心的微小影响。
