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.