Kinetic stability of metal–organic frameworks for corrosive and coordinating gas capture

Abstract

Metal-organic frameworks (MOFs) have demonstrated their utility for a variety of applications involving the storage, separation, and sensing of weakly interacting gases of high purity. Exposure to more realistic, impure gas streams and interactions with corrosive and coordinating gases raises the question of chemical robustness, which remains a paramount concern for practical applications of MOFs. However, factors that determine the stability of MOFs remain incompletely understood. Although past researchers attempted to categorize framework materials as either thermodynamically stable or kinetically stable, recent work has elucidated an energetic penalty for porosity for all materials in this class with respect to a dense material. The metastability of porous phases has important implications for the design of materials for gas storage, heterogeneous catalysts, and electronic materials. Here, we focus on two main strategies for stabilization of the porous phase, either by using inert metal ions, or by increasing the heterolytic metal-ligand bond strength, both of which increase the activation barrier for framework collapse. These two strategies have led to exceptionally robust materials for the capture of coordinating and corrosive gases such as water vapor, ammonia, H2S, SO2, NOx, and even elemental halogens, and we review the progress in designing stable materials for these gases. Looking forward, we envision that the continued pursuit of strategies for kinetic stabilization in the synthesis of new MOFs will provide increasing numbers of robust frameworks suited to harsh conditions, and that short-term stability towards these challenging gases will be predictive of long-term stability for applications in less demanding environments.

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