Novel zeolite framework LMU-2: unveiling of CHA-related structure with active sites by Co-complex structure-directing agent

While alkylammonium salts or organic amines are commonly used as structure-directing agents (SDAs) to synthesize zeolites, metal complexes can also serve this purpose. In this study, we present a novel interrupted framework, which can be regarded as a precursor of the CHA framework type with a pure-silica composition. The polycrystalline yellow powder was synthesized using a cobalt(III)-triazacyclononane complex [Co( tacn ) 2 ] 3+ . Structure determination via 3D electron diffraction revealed details of the [Si–O∙∙∙H∙∙∙O–Si] – hydrogen bonds, which are periodically ordered. They connect the D6R units of the CHA precursor-type structure. Upon calcination, the organic component is removed, yielding a blue material, resulting in the fully connected chabazite structure. The blue color is characteristic for tetrahedrally coordinated Co 2+ , which is most likely located in the chabazite cage and coordinated to the 6-rings of the framework. Temperature-dependent powder diffraction analysis was used to investigate the structural transformation and the discontinuous decrease in the lattice constants a and c of the hexagonal unit cell. Finally, spectroscopic and sorption measurements were conducted to characterize the properties of the material. • Novel zeolite with CHA-related interrupted framework synthesized using Co-complex. • 3D electron diffraction was used for structure determination. • Calcination yields Co-CHA with Co 2+ sites in fully connected chabazite framework. • ΔT-PXRD reveals phase transition and lattice contraction during transformation. • Co-CHA is responsive to NOx exposure—potential for sensing or catalysis.