Evidence of Organic Polymeric Behavior in the Glass Transition of Metal–Organic Frameworks

Abstract

The origin of the glass transition is still an open debate, especially for the new class of glasses, formed from metal‐organic compounds. High‐temperature in situ 2H Nuclear Magnetic Resonance (NMR) experiments are performed on deuterated samples of ZIF‐62 (Zn(C3H4N2)2‐x(C7H6N2)x, with x = 0.25 and x = 0.05), the prototypical metal–organic framework glass former. Using lineshape analysis, frequencies and angular amplitudes of oscillations of the imidazolate ring during heating up to the melt progressively increasing from ≈10 to 150 MHz, and from ≈5° to 25° are found. This behavior is compositionally dependent and points to the origin of the glass transition lying in organic linker movement, in a similar vein to that witnessed in some organics and contrary to the purely inorganic‐based view of Metal–Organic Framework (MOF) glasses taken to date. This experimental approach shows the potential to elucidate the melting and/or decomposition process for a wide range of MOFs.