School of Chemistry, University of Edinburgh, Edinburgh, UK.
Inorg Chem. 2011 Apr 4;50(7):2988-94. doi: 10.1021/ic102457w. Epub 2011 Mar 8.
The equilibrium molecular structure of Si(8)O(12)(OSiMe(3))(8) has been determined in the gas phase by electron diffraction (GED). With OSi-containing substituents on the cage silicon atoms, this molecule contains a moiety, which would, if reproduced in a periodic manner, yield a zeolite-type structure. Extensive ab initio calculations were used to identify two conformers of this molecule, with D(4) and D(2) point-group symmetries; the D(4)-symmetric conformer was approximately 1.2 kJ mol(-1) lower in energy. With 132 atoms in each conformer, this is one of the largest studies to be undertaken using gas electron diffraction. Semiempirical molecular-dynamics (SE-MD) calculations were used to give amplitudes of vibration, vibrational distance corrections (differences between interatomic distances in the equilibrium structure and the vibrationally averaged distances that are given directly by the diffraction data), and anharmonic constants. The structure of Si(8)O(12)(CHCH(2))(8) has also been determined by GED. Calculations showed that the vinyl groups are fairly unhindered and rotate between three minimum-energy positions. Ultimately, all possible combinations of the vinyl groups in these low-energy positions were accounted for in the GED model.
通过电子衍射（GED）确定了 Si(8)O(12)(OSiMe(3))(8) 在气相中的平衡分子结构。由于笼状硅原子上含有 OSi 取代基，如果以周期性方式复制该分子的一部分，将得到沸石型结构。我们使用了广泛的从头算计算来确定该分子的两种构象，它们具有 D(4) 和 D(2) 点群对称性；D(4)对称构象的能量约低 1.2 kJ mol(-1)。对于每个构象的 132 个原子，这是使用气相电子衍射进行的最大研究之一。半经验分子动力学（SE-MD）计算用于给出振动幅度、振动距离校正（平衡结构中的原子间距离与直接由衍射数据给出的振动平均距离之间的差异）和非谐常数。Si(8)O(12)(CHCH(2))(8) 的结构也通过 GED 确定。计算表明，乙烯基基团相当不受阻碍，可以在三个最低能量位置之间旋转。最终，在 GED 模型中考虑了这些低能位置中乙烯基基团的所有可能组合。
