Zeolite CAN and AFI-Type Zeolitic Imidazolate Frameworks with Large 12-Membered Ring Pore Openings Synthesized Using Bulky Amides as Structure-Directing Agents

Using
bulky amides as the structure-directing agents (SDAs) is
an alternative synthetic strategy for the exploration of crystalline
large pore (≥12-membered ring) zeolitic imidazolate frameworks
(ZIFs). Specifically, by using the bulky amides, dibutylformamide
(DBF) and dipropylformamide (DPF) as solvent and imidazole (Im) as
a ligand, two ZIFs mimicking the CAN and AlPO-5 (AFI) zeotypes with
12-membered ring (MR) pore openings were synthesized, and denoted
as CAN-[Zn­(Im)2] and AFI-[Zn­(Im)2], respectively.
These two materials are the first known examples of Zn­(Im)2 polymorphs with 12-MR pores and AFI-[Zn­(Im)2] has the
largest pore apertures reported to date for ZIF materials. The concept
that the bulky amides used were not simply acting as the solvent,
but were in fact acting as SDAs or templates during the synthesis
of the large pore ZIFs, was suggested by the closeness of the geometrical
fit between the guest DBF and the can cages (composite
building units) of the CAN-[Zn­(Im)2].