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A zeolitic imidazolate framework with conformational variety: Conformational polymorphs versus frameworks with static conformational disorder

Springer, S, Baburin, I.A., Heinemeyer, T, Gerrit Schiffmann, J, van Wullen, L, Leoni, Stefano and Wiebcke, M 2016. A zeolitic imidazolate framework with conformational variety: Conformational polymorphs versus frameworks with static conformational disorder. Crystengcomm 18 (14) , pp. 2477-2489. 10.1039/C6CE00312E

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We show via structural considerations and DFT calculations that for a zeolitic imidazolate framework (ZIF) with sodalite (SOD) topology, [Zn(dcim)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 via reconstructive 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 to 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 being located in the domain interfaces. As structural differences appear to be more related to characteristics of the real as opposed to the 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.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Advanced Research Computing @ Cardiff (ARCCA)
Subjects: Q Science > QD Chemistry
Publisher: Royal Society of Chemistry
ISSN: 1466-8033
Date of First Compliant Deposit: 30 March 2016
Date of Acceptance: 2 March 2016
Last Modified: 04 Jun 2017 08:55

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