In all-silica zeolites synthesised via the “fluoride route”, the fluoride anions are typically incorporated in small cages, forming [SiO4F]- trigonal bipyramids. While diffraction and NMR experiments can elucidate the fluoride location(s) and the occurrence/absence of dynamic disorder, they provide limited insights into the factors that determine equilibrium position and dynamic behaviour. To develop a more thorough understanding, electronic structure calculations in the framework of dispersion-corrected density functional theory (DFT) were performed for five all-silica zeolites (NON, STF, IFR, STT, CHA frameworks). DFT-based predictions of the energetically preferred fluoride location within a given cage were mostly in excellent agreement with experiment. Apart from the known tendency of fluoride anions to locate close to small rings, there are no easily generalisable crystal-chemical rules to predict the most probable fluoride sites.DFT-based molecular dynamics calculations were employed to predict and explain the dynamic behaviour of the fluoride anions, which differs markedly among the different frameworks. On the basis of the simulations, it could be determined that local interactions of fluoride anions with framework Si atoms have larger impact on the (non-)occurrence of dynamic disorder than longer-range interactions with the organic structure-directing agents. In addition to providing detailed understanding of the behaviour of fluoride anions in as-synthesised all-silica zeolites, the findings of the present work could contribute to a further elucidation of the structure-directing role of fluoride during zeolite synthesis.

中文翻译：

---

全硅沸石中的氟化物阴离子：使用密度泛函理论计算研究优选的氟化物位点和动态无序

在通过“氟化物途径”合成的全硅沸石沸石中，氟化物阴离子通常掺入小笼中，形成[SiO4F]-三角双锥体。尽管衍射和NMR实验可以阐明氟化物的位置以及动态紊乱的发生/不存在，但它们对确定平衡位置和动态行为的因素的洞察力有限。为了建立更全面的了解，在分散校正的密度泛函理论（DFT）的框架内对五种全硅沸石（NON，STF，IFR，STT，CHA框架）进行了电子结构计算。基于DFT的给定笼内能量优选氟化物位置的预测与实验基本吻合。除了已知的氟阴离子趋向于靠近小环的趋势外，目前尚无易于概括的晶体化学规则来预测最可能的氟化物位点。基于DFT的分子动力学计算可用来预测和解释氟化物阴离子的动力学行为，这在不同的框架之间存在显着差异。在模拟的基础上，可以确定氟阴离子与骨架Si原子的局部相互作用对动态无序（非）发生的影响大于与有机结构导向剂的长距离相互作用。除了提供对合成的全硅沸石中氟阴离子行为的详细了解之外，本工作的发现还有助于进一步阐明氟在沸石合成过程中的结构指导作用。