A zeolitic imidazolate framework with conformational variety: conformational polymorphs versusframeworks with static conformational disorder

We show viastructural considerations and DFT calculations that for a zeolitic imidazolate framework (ZIF) with sodalite (SOD) topology, [Zn(dcim) sub(2)]-SOD (dcim = 4,5-dichloroimidazolate), structural models of an infinite number of hypothetical conformational polymorphs with distinct linker orien...

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Bibliographic Details
Published in:CrystEngComm 2016-03, Vol.18 (14), p.2477-2489
Main Authors: Springer, Sergej, Baburin, Igor A, Heinemeyer, Thea, Schiffmann, Jan Gerrit, van Wuellen, Leo, Leoni, Stefano, Wiebcke, Michael
Format: Article
Language:English
Subjects:
Accessibility
Diffraction
Disorders
Nanostructure
Orientation
Proposals
Solvents
Statistics
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Summary:We show viastructural considerations and DFT calculations that for a zeolitic imidazolate framework (ZIF) with sodalite (SOD) topology, [Zn(dcim) sub(2)]-SOD (dcim = 4,5-dichloroimidazolate), structural models of an infinite number of hypothetical conformational polymorphs with distinct linker orientations can be generated, which can be interconverted most likely only viareconstructive structural transitions. The relative total energies suggest that some of those polymorphs might be synthetically accessible. Efforts in that direction led to the synthesis of new trigonal 1 and previously known cubic 2 with improved crystallinity. According to structural analyses based on powder X-ray diffraction (PXRD) methods supported by NMR spectroscopy, 1 is the most stable of the theoretically predicted SOD-type framework conformers (isostructural to ZIF-7), whereas 2, at variance with a recent proposal, is a SOD-type material with a high degree of orientational disorder of the dcim linker units. The statistics of the linker orientations in 2 is close to that in 1, indicating that the disorder in 2 is not random. Rather, crystals of 2 are likely twins consisting of nanoscopic domains of trigonal 1 that are deformed to a cubic metric, with linker disorder located in the domain interfaces. As structural differences appear to be more related to characteristics of real as opposed to ideal crystal structures, we propose to not consider 1 and 2 as true conformational polymorphs. Systematic investigations of solvent mixtures led to the discovery of intermediate materials of 1 and 2. The PXRD patterns and SEM images indicate that they belong to a complete series of structural intermediates. Differences in the Ar adsorption/desorption behaviours reveal that 1, in contrast to 2, is a flexible ZIF framework.
ISSN:1466-8033
DOI:10.1039/c6ce00312e