Combined experimental and computational NMR study of crystalline and amorphous zeolitic imidazolate frameworks. Issue 38 (9th September 2015)

• Record Type: Journal Article
• Authors: Baxter, Emma F.; Bennett, Thomas D.; Mellot-Draznieks, Caroline; Gervais, Christel; Blanc, Frédéric; Cheetham, Anthony K.
• Is Part Of: Physical chemistry chemical physics. Volume 17:Issue 38(2015)
• Page Start: 25191
• Page End: 25196
• Publication Date: 2015-09-09
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c5cp02552d
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : High resolution 13 C and 15 N CP MAS NMR spectra of ZIF-4, ZIF-8 and ZIF-zni are assigned on the basis of DFT calculations on the geometry-optimized structures. Abstract : Zeolitic imidazolate frameworks (ZIFs) have attracted great interest in recent years due to their high chemical and thermal stability with promising applications in gas storage and separations. We investigate the structures of three different crystalline ZIFs – ZIF-4, ZIF-8, ZIF-zni – and their amorphous counterparts using high field 13 C and 15 N CP MAS NMR. The high field (20 T) allows for the observation of all crystallographically independent carbon and nitrogen atoms in the crystalline ZIFs. Combining our experimental results with density functional theory calculations enabled the assignment of all chemical shifts. The crystalline spectra reveal the potential of high field NMR to distinguish between two ZIF polymorphs, ZIF-4 and ZIF-zni, with identical [Zn(C3 H3 N2 )2 ] chemical compositions. 13 C and 15 N CP MAS NMR data obtained for the amorphous ZIFs clearly showed signal broadening upon amorphization, confirming the retention of chemical composition and the structural similarity of amorphous ZIF-4 and ZIF-zni. In the case of amorphous ZIF-8, we present evidence for the partial de-coordination of the 2-methyl imidazole linker.