Stabilizing Metastable Polymorphs of Metal–Organic Frameworks via Encapsulation of Graphene Oxide and Mechanistic Studies

Polymorphic transition from a metastable phase to a stable phase often occurs in metal–organic frameworks (MOFs) under the action of external stimuli. However, these transitions sometimes result in deteriorating their special performances and can even lead to serious safety problems. Therefore, developing a simple and efficient strategy for enhancing the stabilities of metastable MOF polymorphs is very imperative and meaningful. Herein, we propose a simple graphene oxide (GO)-encapsulating strategy for improving the stabilities of metastable MOF polymorphs. To illustrate this strategy, we designed and synthesized two polymorphic MOFs [MOF(ATA-a) and MOF(ATA-b)] as examples, which are based on energetic 5-amino-1H-tetrazole as ligands. Single-crystal X-ray diffraction showed that these two polymorphs have a same chemical composition [Zn2(ATA)3(ATA)2/2]n, but different space groups, space systems, and different stacking modes of the neighboring ligands. As expected, the metastable polymorph [MOF(ATA-a)] und...