The (p-d) .pi. bonding in fluorosilanes? Gas-phase structures of (CH3)4-nSiFn with n = 1-3 and of (tert-Bu)2SiF2
The (p-d) .pi. bonding in fluorosilanes? Gas-phase structures of (CH3)4-nSiFn with n = 1-3 and of (tert-Bu)2SiF2
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(p-d) .pi。
DOI：
10.1021/ja00274a006
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发表时间：
1986
影响因子：
15
通讯作者：
N. Auner
中科院分区：
文献类型：
--
作者：
B. Rempfer;H. Oberhammer;N. Auner
本文研究了甲基氟硅烷（CH_3）_4_nSiF_n（n = 1-3）和二叔丁基二氟硅烷（n = 3）的气相结构（rg值）。Bu_2SiF_2，用电子衍射法测定。在CH 3SiF 3的情况下，微波旋转常数包括在结构分析中。在甲基氟硅烷系列中，观察到Si-F和Si-C键长随着η的增加而稳定减小：对于（CH 3）3SiF，（CH 3）2SiF 2和CH 3SiF 3，Si-F= 1.600（2），1.586（2）和1.570（2）η，Si-C= 1.848（2），1.836（2）和1.828（4）η。这些趋势是合理的增加极性的贡献和收缩的硅价层。SiF 4的从头计算表明（pd）键可以忽略不计。在（CH_3）_2SiF_2中，甲基被叔丁基取代后，Si-F键和Si-C键变长，硅键角变化很大：Si-F= 1.586（2），1.606（4），Si-C= 1.836（2），1.869（3），CSiC= 116.7（6），125.5（11）;在（CH_3）_2SiF_2和Z-Bu_2SiF_2中，FSiF分别为104.6（4），97.7（8）.由于硅化合物的某些性质与类似的碳或锗衍生物有很大的不同，因此硅化合物的成键性质一直受到人们的关注.在这些性质中，结构特征例如实验Si-X键长（见表I）总是短于相应共价半径的总和。如Schomaker-Stevenson所建议的那样，如果考虑到由于电负性差异引起的极性效应，那么对Si-C键的预测非常接近实验值，但是具有更多电负性原子X的Si-X键仍然被预测为太长。差值单调增加
Thegas-phase structures (rg values) of the methylfluorosilanes (CH3) 4_ „SiF „with= 1-3 and of di-ierz-butyl-difluorosilane,?-Bu2SiF2, have been determined by electron diffraction. In the case of CH3SiF3 the microwave rotational constant was included in the structure analysis. In the methylfluorosilane series a steady decrease of Si-F and Si-C bond lengths is observed with increasing fluorination: Si-F= 1.600 (2), 1.586 (2), and 1.570 (2) Á and Si-C= 1.848 (2), 1.836 (2), and 1.828 (4) Á for (CH3) 3SiF,(CH3) 2SiF2, and CH3SiF3, respectively. These trends are rationalized by increasing polar contributions and contraction of the silicon valence shell. Ab initio calculations for SiF4 indicate that (pd) bonding is negligible. Substitution of the methyl groups in (CH3) 2SiF2 by tert-butyl groups leads to lengtheningof Si-F and Si-C bonds and strong variations in the silicon bond angles: Si-F= 1.586 (2), 1.606 (4) A; Si-C= 1.836 (2), 1.869 (3) A; CSiC= 116.7 (6), 125.5 (11); and FSiF= 104.6 (4), 97.7 (8) in (CH3) 2SiF2 and Z-Bu2SiF2, respectively.The bonding properties in silicon compounds have attracted considerable interest for many years, because some properties of these compounds differ strongly from those of analogous carbon or germanium derivatives. Among these properties are structural features such as experimental Si-X bond lengths (see Table I), which are always shorter than the sum of the respective covalent radii. If polar effects due to electronegativity differences are taken into account, as suggested by Schomaker-Stevenson, 6 the prediction for the Si-C bond is very close to the experimental value, but Si-X bonds with more electronegative atoms X are still predicted tobe too long. The difference increases monotonically