A zeolitic imidazolate framework with conformational variety: conformational polymorphs versus frameworks with static conformational disorder. Issue 14 (17th March 2016)

• Record Type: Journal Article
• Authors: Springer, Sergej; Baburin, Igor A.; Heinemeyer, Thea; Schiffmann, Jan Gerrit; van Wüllen, Leo; Leoni, Stefano; Wiebcke, Michael
• Is Part Of: CrystEngComm. Volume 18:Issue 14(2016)
• Page Start: 2477
• Page End: 2489
• Publication Date: 2016-03-17
• Subjects: Crystals -- Periodicals; Crystal growth -- Periodicals; Crystallography -- Periodicals; Cristaux -- Périodiques; Cristaux -- Croissance -- Périodiques; Cristallographie -- Périodiques; 548
• DOI: 10.1039/c6ce00312e
• Languages: English
• ISSNs: 1466-8033

Abstract

Abstract : Two forms of a SOD-type ZIF with distinct linker orientations exhibit different sorption behaviours. Abstract : 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 trigonal1 and previously known cubic2 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), whereas2, 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 in2 is close to that in1, indicating that the disorder in2 is not random. Rather, crystals of2 are likely twins consisting of nanoscopic domains of trigonal1 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 consider1 and2 as true conformational polymorphs. Systematic investigations of solvent mixtures led to the discovery of intermediate materials of1 and2 . 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 that1, in contrast to2, is a flexible ZIF framework.