Synthesis and Properties of a Compositional Series of MIL-53(Al) Metal-Organic Framework Crystal-Glass Composites

Metal-organic framework crystal-glass composites (MOF-CGCs) are materials in which a crystalline MOF is dispersed within a MOF glass. In this work, we explore the room temperature stabilization of the open-pore form of MIL-53(Al), usually observed at high-temperature, which occurs upon encapsulation within a ZIF-62(Zn) MOF glass matrix. A series of MOF-CGCs containing different loadings of MIL-53(Al) were synthesized and characterized using X-ray diffraction and nuclear magnetic resonance spectroscopy. An upper limit of MIL-53(Al) that can be stabilized in the composite was determined for the first time. The nanostructure of the composites was probed using pair distribution function analysis and scanning transmission electron microscopy. Notably, the distribution and integrity of the crystalline compo-nent in a sample series was determined, and these findings related to the MOF-CGC gas adsorption capacity in order to identify the optimal loading necessary for maximum CO2 sorption capacity.TDB would like to thank both the Royal Society for a University Research Fellowship (UF150021) and the Royal Society for a Research Grant (RG94426). CWA would like to thank the Royal Society for a PhD studentship (RG160498), and the Commonwealth Scientific and Industrial Research Council for additional support (C2017/3108). Both JH and TDB gratefully acknowledge the EPSRC (EP/R015481/1). AFS acknowledges EPSRC for a studentship award under the Doctoral Training Programme. AMB acknowledges the Royal Society for funding (RGF\EA\180092), as well as the Cambridge Trust for a Vice Chancellor’s Award (304253100). We extend our gratitude to Diamond Light Source, Rutherford Appleton Laboratory, UK, for access to Beamline I15-1 (EE20038-1) and access and support in the use of the electron Physical Science Imaging Centre (EM20195). SMC acknowledges the Henslow Research Fellowship at Girton College, Cambridge. PAM thanks the EPSRC for financial support under grant number EP/R025517/1

Metal-organic framework and inorganic glass composites

Abstract: Metal-organic framework (MOF) glasses have become a subject of interest as a distinct category of melt quenched glass, and have potential applications in areas such as ion transport and sensing. In this paper we show how MOF glasses can be combined with inorganic glasses in order to fabricate a new family of materials composed of both MOF and inorganic glass domains. We use an array of experimental techniques to propose the bonding between inorganic and MOF domains, and show that the composites produced are more mechanically pliant than the inorganic glass itself

Melting of hybrid organic-inorganic perovskites.

Several organic-inorganic hybrid materials from the metal-organic framework (MOF) family have been shown to form stable liquids at high temperatures. Quenching then results in the formation of melt-quenched MOF glasses that retain the three-dimensional coordination bonding of the crystalline phase. These hybrid glasses have intriguing properties and could find practical applications, yet the melt-quench phenomenon has so far remained limited to a few MOF structures. Here we turn to hybrid organic-inorganic perovskites-which occupy a prominent position within materials chemistry owing to their functional properties such as ion transport, photoconductivity, ferroelectricity and multiferroicity-and show that a series of dicyanamide-based hybrid organic-inorganic perovskites undergo melting. Our combined experimental-computational approach demonstrates that, on quenching, they form glasses that largely retain their solid-state inorganic-organic connectivity. The resulting materials show very low thermal conductivities (~0.2 W m-1 K-1), moderate electrical conductivities (10-3-10-5 S m-1) and polymer-like thermomechanical properties

Mixed hierarchical local structure in a disordered metal–organic framework

Abstract: Amorphous metal–organic frameworks (MOFs) are an emerging class of materials. However, their structural characterisation represents a significant challenge. Fe-BTC, and the commercial equivalent Basolite® F300, are MOFs with incredibly diverse catalytic ability, yet their disordered structures remain poorly understood. Here, we use advanced electron microscopy to identify a nanocomposite structure of Fe-BTC where nanocrystalline domains are embedded within an amorphous matrix, whilst synchrotron total scattering measurements reveal the extent of local atomic order within Fe-BTC. We use a polymerisation-based algorithm to generate an atomistic structure for Fe-BTC, the first example of this methodology applied to the amorphous MOF field outside the well-studied zeolitic imidazolate framework family. This demonstrates the applicability of this computational approach towards the modelling of other amorphous MOF systems with potential generality towards all MOF chemistries and connectivities. We find that the structures of Fe-BTC and Basolite® F300 can be represented by models containing a mixture of short- and medium-range order with a greater proportion of medium-range order in Basolite® F300 than in Fe-BTC. We conclude by discussing how our approach may allow for high-throughput computational discovery of functional, amorphous MOFs

Interfacial Bonding between a Crystalline Metal-Organic Framework and an Inorganic Glass.

The interface within a composite is critically important for the chemical and physical properties of these materials. However, experimental structural studies of the interfacial regions within metal-organic framework (MOF) composites are extremely challenging. Here, we provide the first example of a new MOF composite family, i.e., using an inorganic glass matrix host in place of the commonly used organic polymers. Crucially, we also decipher atom-atom interactions at the interface. In particular, we dispersed a zeolitic imidazolate framework (ZIF-8) within a phosphate glass matrix and identified interactions at the interface using several different analysis methods of pair distribution function and multinuclear multidimensional magic angle spinning nuclear magnetic resonance spectroscopy. These demonstrated glass-ZIF atom-atom correlations. Additionally, carbon dioxide uptake and stability tests were also performed to check the increment of the surface area and the stability and durability of the material in different media. This opens up possibilities for creating new composites that include the intrinsic chemical properties of the constituent MOFs and inorganic glasses

Metal-organic framework gels and monoliths.

The synthesis of metal-organic frameworks (MOFs) has, to date, largely been in the form of crystalline powders. However, interest in different physical morphologies of this class of materials is growing. In this perspective, we provide an overview of the structure, properties and applications of MOF monoliths. In particular, we explore the complex synthetic landscapes associated with MOF crystallization and discuss the synthetic factors leading to the formation of MOF gels, i.e. the precursor to sol-gel MOF monoliths. Finally, we provide our thoughts on the future development of this field, and attempt to highlight the importance of the MOF gel state in the discovery of new functional materials

Transient intermediate in the formation of an amorphous metal-organic framework.

Acknowledgements: AFS acknowledges the EPSRC for a PhD studentship award under the industrial CASE scheme, along with Johnson Matthew PLC (JM11106). MFT acknowledges Corning Incorporated for a PhD studentship. TDB thanks the Royal Society for both a University Research Fellowship (URF\R\211013) and a research grant (RGS\R2\212221). TDB and CCB acknowledge funding from a Leverhulme Trust Research Project Grant (RPG-2020-005). We would thank Diamond Light Source for the provision of beam time at the I20-EDE beamline (Experiment Number SP28536-1). AFS would also like to thank Dr Hamish Yeung (University of Birmingham) for useful discussions regarding nucleation and MOF formation.Amorphous metal-organic frameworks are rarely formed via direct synthesis. Our limited understanding of their atomic assembly in solution prevents full exploitation of their unique structural complexity. Here, we use in situ synchrotron X-ray absorption spectroscopy with sub-second time resolution to probe the formation of the amorphous Fe-BTC framework. Using a combination of spectral fingerprinting, linear combination analysis, and principal component analysis coupled with kinetic analyses, we reveal a multi-stage formation mechanism that, crucially, proceeds via the generation of a transient intermediate species

Compositional inhomogeneity and tuneable thermal expansion in mixed-metal ZIF-8 analogues

We study the structural and thermomechanical effects of cation substitution in the compositional family of metal–organic frameworks Zn1−xCdx(mIm)2 (HmIm = 2-methylimidazole). We find complete miscibility for all compositions x, with evidence of inhomogeneous distributions of Cd and Zn that in turn affect framework aperture characteristics. Using variable-temperature X-ray powder diffraction measurements, we show that Cd substitution drives a threefold reduction in the magnitude of thermal expansion behaviour. We interpret this effect in terms of an increased density of negative thermal expansion modes in the more flexible Cd-rich frameworks

Modeling the Effect of Defects and Disorder in Amorphous Metal-Organic Frameworks.

Funder: FP7 Ideas: European Research Council; doi: 10.13039/100011199; Grant(s): 758370Amorphous metal-organic frameworks (aMOFs) are a class of disordered framework materials with a defined local order given by the connectivity between inorganic nodes and organic linkers, but absent long-range order. The rational development of function for aMOFs is hindered by our limited understanding of the underlying structure-property relationships in these systems, a consequence of the absence of long-range order, which makes experimental characterization particularly challenging. Here, we use a versatile modeling approach to generate in silico structural models for an aMOF based on Fe trimers and 1,3,5-benzenetricarboxylate (BTC) linkers, Fe-BTC. We build a phase space for this material that includes nine amorphous phases with different degrees of defects and local order. These models are analyzed through a combination of structural analysis, pore analysis, and pair distribution functions. Therefore, we are able to systematically explore the effects of the variation of each of these features, both in isolation and combined, for a disordered MOF system, something that would not be possible through experiment alone. We find that the degree of local order has a greater impact on structure and properties than the degree of defects. The approach presented here is versatile and allows for the study of different structural features and MOF chemistries, enabling the derivation of design rules for the rational development of aMOFs

Mapping nanocrystalline disorder within an amorphous metal-organic framework.

Acknowledgements: A.F.S. acknowledges the Engineering and Physical Sciences Research Council (EPSRC) for a PhD studentship award under the industrial CASE scheme, along with Johnson Matthey PLC (JM11106). T.D.B. acknowledges the Royal Society for a University Research Fellowship (URF\R\211013). S.M.C. acknowledges support from the EPSRC (EP/V044907/1). C.S. acknowledges financial support from the China Scholarship Council (CSC) (Grant No. 202006630025). We would like to thank the Diamond Light Source, Rutherford Appleton Laboratory, U.K., for access to ePSIC (EM20198-7). In particular, we thank Dr. Mohsen Danaie for his assistance during our beamtime.Intentionally disordered metal-organic frameworks (MOFs) display rich functional behaviour. However, the characterisation of their atomic structures remains incredibly challenging. X-ray pair distribution function techniques have been pivotal in determining their average local structure but are largely insensitive to spatial variations in the structure. Fe-BTC (BTC = 1,3,5-benzenetricarboxylate) is a nanocomposite MOF, known for its catalytic properties, comprising crystalline nanoparticles and an amorphous matrix. Here, we use scanning electron diffraction to first map the crystalline and amorphous components to evaluate domain size and then to carry out electron pair distribution function analysis to probe the spatially separated atomic structure of the amorphous matrix. Further Bragg scattering analysis reveals systematic orientational disorder within Fe-BTC's nanocrystallites, showing over 10° of continuous lattice rotation across single particles. Finally, we identify candidate unit cells for the crystalline component. These independent structural analyses quantify disorder in Fe-BTC at the critical length scale for engineering composite MOF materials