Zwijnenburg Martijn A, Simperler Alexandra, Wells Stephen A, Bell Robert G
J Phys Chem B. 2005 Aug 11;109(31):14783-5. doi: 10.1021/jp0531309.
We report a computational study on the distortion of SiO4 tetrahedra in zeolite frameworks. For all previously observed frameworks, the tetrahedral mismatch was found to span a narrow range (1.0 x 10(-3) to 2.5 x 10(-2) angstroms2) of values, in contrast to the hypothetical frameworks, which were calculated to have a much wider range of mismatch values. The energy of the frameworks was not found to be a function of the tetrahedral distortion for the previously observed and moderately distorted (tetrahedral mismatch <2.5 x 10(-2) angstroms2) hypothetical frameworks. In contrast, the energy of the bulk of the hypothetical frameworks was shown to be a strong function of the tetrahedral distortion. The fact that the framework energies of some hypothetical frameworks lie much higher than both those of the observed frameworks and the values we would expect from our previously developed topological method (the so-called energetic packing penalty) is explained in terms of the tetrahedral distortion contribution to the framework energy which is negligible for the observed frameworks. Finally, it is hypothesized that the absence of tetrahedral distortion is pivotal for a framework to be experimentally realized, in which case a large fraction of hypothetical frameworks are unrealizable and will forever remain in the realms of the abstract.
我们报告了一项关于沸石骨架中SiO4四面体畸变的计算研究。对于所有先前观察到的骨架，发现四面体失配值分布在一个狭窄的范围内（1.0×10⁻³至2.5×10⁻²埃²），这与假设的骨架形成对比，后者计算得出的失配值范围要宽得多。对于先前观察到的以及适度畸变（四面体失配<2.5×10⁻²埃²）的假设骨架，未发现骨架能量是四面体畸变的函数。相比之下，大部分假设骨架的能量显示为四面体畸变的强函数。一些假设骨架的骨架能量远高于观察到的骨架能量以及我们先前开发的拓扑方法所预期的值（即所谓的能量堆积罚分），这一事实可以用四面体畸变对骨架能量的贡献来解释，而对于观察到的骨架，这种贡献可忽略不计。最后，据推测，不存在四面体畸变对于一个骨架能否通过实验实现至关重要，在这种情况下，很大一部分假设骨架是无法实现的，将永远停留在抽象领域。
