Elucidation of flexible metal-organic frameworks: Research progresses and recent developments

Flexibility is a unique property of metal-organic frameworks (MOFs) that differentiates them from other rigid inorganic porous materials such as zeolites and porous silica. Flexible frameworks are not only scientifically interesting, but also applicable for real-world gas storage/delivery, separation, sensing, and catalysis. So far, a plethora of MOFs with flexible frameworks, termed as ‘soft porous crystal’, ‘flexible MOF’, ‘breathing MOF’, ‘sponge-like MOF’ or ‘dynamic MOF’, has emerged as a new subclass of MOFs. In this review, we discuss diverse perspectives and approaches to understand and control the flexible behaviour in an archetypal MOF platform so that the basic principles can be imparted to the broad community of chemists, materials scientists, and engineers. In addition, potential applications of flexible MOFs will be briefly introduced along with advanced analytic tools and molecular modelling that aid the exploration of the flexibility of MOFs in various conditions and widen the insight to design of novel flexible MOFs.