STA-20: An ABC‑6 Zeotype Structure Prepared by Co-Templating and Solved via a Hypothetical Structure Database and STEM-ADF Imaging

A microporous silicoaluminophosphate with a novel topology type, STA-20, has been prepared via a dual templating method using hexamethylene bisdiazabicyclooctane (diDABCO-C6) and trimethylamine as cotemplates. Its structure has been solved and confirmed using a multitechnique approach that included the use of a hypothetical zeolite database to obtain a candidate starting structure, followed by scanning transmission electron microscopy with annular dark field imaging and Rietveld refinement. STA-20 is a member of the ABC-6 family of zeotype structures. The structure has trigonal symmetry, P-31c, with a = 13.15497(18) Å and c = 30.5833(4) Å in the calcined form. It has a 12-layer stacking sequence of 6-rings (6Rs), AABAABAACAAC­(A), which contains single and double 6R units. In addition to d6r, can, and gme cages, STA-20 possesses the longest cage observed in an ordered ABC-6 material, giving a 3D-connected pore system limited by 8R windows. Models for the location of the templates within cages of the framework were obtained by combining elemental analysis, 13C MAS NMR, computer modeling, and Rietveld refinement.

采用双模板法，以六亚甲基双二氮杂双环辛烷（hexamethylene bisdiazabicyclooctane，缩写diDABCO-C6）与三乙胺作为共模板剂，成功合成了具有新型拓扑结构的微孔硅铝磷酸盐（microporous silicoaluminophosphate）STA-20。该材料的结构通过多技术手段解析并确证：首先借助假想沸石数据库（hypothetical zeolite database）获取候选初始结构，随后结合环形暗场扫描透射电子显微镜（scanning transmission electron microscopy with annular dark field imaging）成像与里特维尔德精修（Rietveld refinement）完成结构验证。STA-20隶属于ABC-6族类沸石结构，其结构具有三方晶系对称性，空间群为P-31c；焙烧态下的晶胞参数为a = 13.15497(18) Å，c = 30.5833(4) Å。该结构的六元环（6-rings，6R）堆叠序列为12层的AABAABAACAAC(A)模式，包含单六元环与双六元环单元。除d6r笼、can笼与gme笼外，STA-20还拥有有序ABC-6类材料中迄今观测到的最长笼结构，由此形成了受限于八元环（8R）窗口的三维连通孔道体系。通过结合元素分析、碳-13魔角旋转核磁共振谱（13C MAS NMR）、计算机模拟与里特维尔德精修，研究人员得到了模板剂在骨架笼内的定位模型。