Insights into the pores of microwave-assisted metal-imidazolate frameworks showing enhanced gas sorption

Microwave heating (MW)-assisted synthesis has been widely applied as an alternative method for the chemical synthesis of organic and inorganic materials. In this work, we report MW-assisted synthesis of three isostructural 3D frameworks with a flexible linker arm of the chelating linker 2-substitute...

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Bibliographic Details
Published in:Dalton transactions : an international journal of inorganic chemistry 2017-04, Vol.46 (14), p.4824-4833
Main Authors: Mondal, Suvendu Sekhar, Dey, Subarna, Attallah, Ahmed G, Krause-Rehberg, Reinhard, Janiak, Christoph, Holdt, Hans-Jürgen
Format: Article
Language:English
Subjects:
Chelating
Heating
Pore size
Porosity
Positron annihilation
Sorption
Synthesis
Synthesis (chemistry)
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Summary:Microwave heating (MW)-assisted synthesis has been widely applied as an alternative method for the chemical synthesis of organic and inorganic materials. In this work, we report MW-assisted synthesis of three isostructural 3D frameworks with a flexible linker arm of the chelating linker 2-substituted imidazolate-4-amide-5-imidate, named IFP-7-MW (M = Zn, R = OMe), IFP-8-MW (M = Co; R = OMe) and IFP-10-MW (M = Co; R = OEt) (IFP = Imidazolate Framework Potsdam). These chelating ligands were generated in situ by partial hydrolysis of 2-substituted 4,5-dicyanoimidazoles under MW- and also conventional electrical heating (CE)-assisted conditions in DMF. The structure of these materials was determined by IR spectroscopy and powder X-ray diffraction (PXRD) and the identity of the materials synthesized under CE-conditions was established. Materials obtained from MW-heating show many fold enhancement of CO and H uptake capacities, compared to the analogous CE-heating method based materials. To understand the inner pore-sizes of IFP structures and variations of gas sorptions, we performed positron annihilation lifetime spectroscopy (PALS), which shows that MW-assisted materials have smaller pore sizes than materials synthesized under CE-conditions. The "kinetically controlled" MW-synthesized material has an inherent ability to trap extra linkers, thereby reducing the pore sizes of CE-materials to ultra/micropores. These ultramicropores are responsible for high gas sorption.
ISSN:1477-9226
1477-9234
DOI:10.1039/c7dt00350a