Hybrid glasses from melt-quenched metal-organic frameworks (MOFs) have
been emerging as a new class of materials, which combine the functional
properties of crystalline MOFs with the processability of glasses.
However, only a handful of the vast variety of crystalline MOFs have
been identified as being meltable. Porosity and metal-linker interaction
strength have both been identified as crucial parameters in the
trade-off between thermal decomposition of the organic linker and, more
desirably, melting. For example, the inability of the prototypical
zeolitic imidazolate framework (ZIF) ZIF-8 to melt, is ascribed to the
instability of the organic linker upon dissociation from the metal
center. Here, we demonstrate that the incorporation of an ionic liquid
(IL) into the porous interior of ZIF-8 provides a means to reduce its
melting temperature to below its thermal decomposition temperature (Tm
< Td). Experimental evidence shows that the Tm of ZIF-8 obtained by
IL infiltration is around 381 °C, and that the glass forming ability
(Tg/Tm) of such melts is above 0.9, i.e. higher than those previously
reported for other meltable MOFs. Our structural studies show that the
prevention of decomposition, and successful melting, is due to the IL
interactions stabilizing the rapidly dissociating ZIF-8 linkers upon
heating. This understanding may act as a general guide for extending the
range of meltable MOF materials and, hence, the chemical and structural
variety of MOF-derived glasses.</div
