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July, 2018

Metal–organic frameworks (MOFs), or networked structures of inorganic nodes connected by organic ligands, are flexible materials that can be broadly separated into two classes according to their porosity. Those that contain high internal surface areas are of intense interest for gas separations and catalysis, while dense MOF materials are investigated for their potential in other applications, e.g., conduction and magnetism. The liquid and glass states of metal–organic frameworks (MOFs) have recently become of interest due to the potential for liquid-phase separations and ion transport, alongside the fundamental nature of the latter as a new, fourth category of melt-quenched glass. Here we show that the MOF liquid state of ZIF-62, [Zn(C3H3N2)1.75(C7H5N2)0.25] can be blended with another MOF component [Co(C3H3N2)2], resulting in a domain structured MOF glass with a single, tailorable glass transition. Intra-domain connectivity and short range order is confirmed by nuclear magnetic resonance spectroscopy and pair distribution function measurements. The interfacial binding between MOF domains in the glass state is evidenced by electron tomography, and the relationship between domain size and Tg investigated.

Figure caption: EDS tomography of a (ZIF-4-Co)0.5(ZIF-62)0.5 glass particle. a Two-dimensional analyses by ADF-STEM showing the particle morphology and EDS chemical maps of Co and Zn. Scale bar is 500 nm. b A volume rendering of the tomographic reconstructions for the Co and Zn signals (two orthogonal viewing directions). cd Discrete two-dimensional slices from the three-dimensional volume reconstruction for Zn plotted with the transected volume rendering of the Co reconstruction. Two protrusions from the principal Co domain are highlighted with the numbers 1 and 2. These highlight the extent of three-dimensional spatial overlap in Co and Zn in cd.

L. Longley, S. M. Collins, C. Zhou, G. J. Smales, S. E. Norman, N. J. Brownbill, C. W. Ashling, P. A. Chater, R. Tovey, C. Bibiane-Schønlieb, T. F. Headen, N. Terrill, Y. Yue, A. J. Smith, F. Blanc, D. A. Keen, P. A. Midgley and T. D. Bennett, “Liquid Phase Blending of Metal-Organic Frameworks”, Nature Commun. (2018).