Unexpected Crystallization Patterns of Zinc Boron Imidazolate Framework ZBIF‐1: NMR Crystallography of Integrated Metal–Organic Frameworks

Abstract

Framework materials, that is, metal-organic frameworks (MOFs) and inorganic frameworks (zeolites), are porous systems with regular structures that provide valuable properties suitable for sorption, catalysis, molecular sieving, and so on. Herein, an efficient, experimental/computational strategy is presented that allows detailed characterization of a polycrystalline MOF system, namely, zinc boron imidazolate framework ZBIF-1, with two integrated unit cells on the atomic-resolution level. Although high-resolution H, B, C, and N MAS NMR spectra provide valuable structural information on the coexistence of two distinct asymmetric units in the investigated system, an NMR crystallography approach combining X-ray powder diffraction, solid-state NMR spectroscopy, and DFT calculations allowed the exact structure of the secondary crystalline phase to be firmly defined and, furthermore, the mutual interconnectivity of the two crystalline frameworks to be resolved. Thus, this study shows the versatility and efficiency of solid-state NMR crystallography for the investigation of the wide family of MOF materials with their extensive structural complexity.

NMR Crystallography of the Polymorphs of Metergoline

“…Additionally, some of its notable applications were most recently discussed by Brown et al [7] and by Emsley et al [8]. Our group successfully employed NMR crystallography in the structural elucidation/refinement of framework materials [9], bioactive compounds [10], and drugs [11][12][13]. Here, further extensions of the NMR crystallography methodology are described, together with results that were obtained for the two known crystal modifications (polymorphs) of the active pharmaceutical ingredient (API) metergoline, which is an established serotonin antagonist [14].…”

NMR-Enhanced Crystallography Aids Open Metal–Organic Framework Discovery Using Solvent-Free Accelerated Aging

“…25,26 While SSNMR has been used to study crystalline or amorphous MOFs and guest inclusion, [27][28][29][30][31][32][33][34][35][36][37][38] there have been relatively few reports of the elucidation of the full structure of MOF using NMR. 39,40 Importantly, the role of NMR spectroscopy in structural characterization of new organic or metalorganic materials is typically limited to quantification of the contents of the asymmetric unit, specifically determination of Z' (i.e., the number of molecules in the asymmetric unit). [41][42][43][44][45] Whereas the principal goal of AA is minimalistic synthesis, here we show that it also offers an opportunity to discover new open-framework materials.…”

“…It is well suited to studies of both ordered and disordered materials, − providing valuable information on short-range order. NMR-enhanced crystallography combines information on the local structure (SSNMR) with details on long-range order (powder X-ray diffraction, PXRD) for elucidating structures of solids. , Although SSNMR has been used to study crystalline or amorphous MOFs and guest inclusion, − there have been relatively few reports of the elucidation of the full structure of MOF using NMR. , Importantly, the role of NMR spectroscopy in structural characterization of new organic or metal–organic materials is typically limited to quantification of the contents of the asymmetric unit, specifically determination of Z ′ (i.e., the number of molecules in the asymmetric unit). − …”

Gallium Species Incorporated into MOF Structure: Insight into the Formation of a 3D Polycrystalline Gallium–Imidazole Framework

“…A solid-state NMR crystallography approach combining X-ray powder diffraction (XRPD), solid-state NMR techniques (ssNMR), and quantum-chemical calculations is particularly suited to the structural investigation of complex porous materials. It has long been used for the elucidation of miscellaneous structural motifs in MOF networks. − Moreover, all triel/icosagen elements are suitable for NMR measurements because they have an adequate sensitivity and gyromatic ratio and relatively easily resolved structural features. In particular, for Ga and In the use of higher magnetic fields (>14.1 T) is often necessary.…”