# Low-Dimensional Zeotypes Templated by Stacked Cyclic Benzimidazolium Revealed by Electron Crystallography

## TL;DR

Researchers discovered new low-dimensional zeolitic materials using benzimidazolium cations and studied their transformation into three-dimensional zeolites.

## Contribution

The study reveals how benzimidazolium cations direct the formation of low-dimensional zeolites and their transformation into new 3D frameworks.

## Key findings

- Three low-dimensional zeolitic materials (EMM-75P, EM-L01, EM-L02) were synthesized using benzimidazolium cations.
- Upon calcination, EMM-75P transforms into a new 3D zeolite with a previously unknown framework topology.
- The structural characterization provides insights into topotactic condensation mechanisms.

## Abstract

The structural diversity
of zeolites depends strongly on the use
of organic structure-directing agents (OSDAs) that guide their formation.
Low-dimensional zeolitic materials, such as layered or chain-like
phases, can serve as key intermediates in topotactic condensation
pathways, yet the mechanisms governing their formation and transformation
remain poorly understood. Here, we report three low-dimensional zeolitic
materials, EMM-75P, EM-L01, and EM-L02, synthesized using benzimidazolium
cations as OSDAs. Their structures were determined by three-dimensional
electron diffraction (3D ED), including the atomic structure of the
OSDAs, revealing their confinement within the framework to shed light
on their structure-directing role. The bulky benzimidazolium OSDAs
prevent the formation of materials with three-dimensional framework
structures and instead direct the formation of low-dimensional zeotypes.
Upon calcination, the two-dimensional layered aluminosilicate zeotype
EMM-75P undergoes topotactic condensation to form a three-dimensional
zeolite, EMM-75, with a previously unreported zeolite framework topology.
Aluminosilicate EM-L01 is a 2D analogue of STF/SFF zeolite frameworks and partially condensed to an STF-topology upon calcination, whereas EM-L02, a 1D silicate
composed of double 6-ring chains, packed analogous to the CHA zeolite framework, collapses during the thermal treatment. The detailed
structural characterization of these three materials provides insights
into the mechanism of topotactic condensation and demonstrates how
such pathways can lead to new zeolite materials.