How to Make the Ionic Si-O Bond More Covalent and the Si-O-Si Linkage a Better Acceptor for Hydrogen Bonding
How to Make the Ionic Si-O Bond More Covalent and the Si-O-Si Linkage a Better Acceptor for Hydrogen Bonding
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DOI：
10.1021/ic900074r
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发表时间：
2009-05-18
影响因子：
4.6
通讯作者：
Beckmann, Jens
中科院分区：
文献类型：
--
作者：
Grabowsky, Simon;Hesse, Maxie F.;Beckmann, Jens
键角的变化可以调节化合物的反应性。为了验证这一概念，通过对分子模型化合物H_3SiOSiH_3，（H_3Si）（2）O centerdot centerdot HOH，（H_3Si）（2）O centerdot centerdot HOH，和（H3 Si）（2）O中心点中心点HOSiH 3和高分辨同步辐射X射线衍射实验，3-二氢-1，1，3，3-四甲基-2，1，3-苯并恶二硅杂环戊烯（1），一种分子化合物，可在硅烷醇基团和硅氧烷键之间形成非常罕见的分子间氢键。对于理论计算和实验，电子描述符来自于电子密度（艾德）分布和电子局域化函数（ELF）的拓扑分析。实验获得的ELF的拓扑分析是一个新发展的方法。这些描述符表明，硅-O键的字符和碱性的硅氧烷连接强烈依赖于Si-O-Si角。虽然Si-O键的离子键特征占主导地位，但当Si-O-Si角从线性减小到四面体角附近的值时，共价键的贡献变得更加显着，并且碱性增加。因此，观察到1的例外分子间氢键的存在可以解释其非常小的应变Si-O-Si角，采用近四面体角。
Variation of a bond angle can tune the reactivity of a chemical compound. To exemplify this concept, the nature of the siloxane linkage (Si-O-Si), the most abundant chemical bond in the earth's crust, was examined using theoretical calculations on the molecular model compounds H3SiOSiH3, (H3Si)(2)O center dot center dot center dot HOH, and (H3Si)(2)O center dot center dot center dot HOSiH3 and high-resolution synchrotron X-ray diffraction experiments on 5-dimethylhydroxysilyl-1,3-dihydro-1,1,3,3-tetramethyl-2,1,3-benzoxadisilole (1), a molecular compound that gives rise to the formation of very rare intermolecular hydrogen bonds between the silanol groups and the siloxane linkages. For theoretical calculations and experiment, electronic descriptors were derived from a topological analysis of the electron density (ED) distribution and the electron localization function (ELF). The topological analysis of an experimentally obtained ELF is a newly developed methodology. These descriptors reveal that the Si-O bond character and the basicity of the siloxane linkage strongly depend-on the Si-O-Si angle. While the ionic bond character is dominant for Si-O bonds, covalent bond contributions become more significant and the basicity increases when the Si-O-Si angle is reduced from linearity to values near the tetrahedral angle. Thus, the existence of the exceptional intermolecular hydrogen bond observed for 1 can be explained by its very small strained Si-O-Si angle that adopts nearly a tetrahedral angle.