Flux Melting of Metal-Organic Frameworks

Recent demonstrations of melting in the metal-organic framework (MOF) family have created
interest in the interfacial domain between inorganic glasses and amorphous organic polymers. The
chemical and physical behaviour of porous hybrid liquids and glasses is of particular interest,
though opportunities are limited by the inaccessible melting temperatures of many MOFs. Here,
we show that the synthetic processing technique of flux melting, ‘borrowed’ from the inorganic
domain, may be applied to MOFs in order to melt materials which do not possess an accessible
liquid state in their pure form. We employ the high-temperature liquid state of one MOF as a solvent
for a secondary, non-melting MOF component. Differential scanning calorimetry, small- and wideangle
X-ray scattering, electron microscopy and X-ray total scattering techniques are used to show
the flux melting of the crystalline component within the liquid. Gas adsorption and positron
annihilation lifetime spectroscopy measurements show that this results in enhanced, accessible
porosity to a range of guest molecules, in the resultant flux melted MOF glass.