Crystal engineering is the field of chemistry that studies the design, properties, and application of crystals. An aspect of crystal engineering is the design of coordination networks formed by the rational combination of metal nodes and organic linker ligands. Porous coordination networks, which are also known as porous coordination polymers (PCPs), Metal Organic Materials (MOMs) or Metal Organic Frameworks (MOFs), have captured the interest of researchers worldwide because of their inherent modularity and amenability to crystal engineering principles. PCPs and porous MOMs have been classified into four generations: 1st generation materials collapse on guest removal and lose crystallinity; 2nd generation materials possess a rigid nature upon guest insertion/removal and exhibit a type I isotherm; 3rd generation materials alter their original structure and maintain overall framework connectivity when exposed to external stimuli such as guest incorporation/removal, pressure and heat; 4th generation materials can be fine-tuned via post synthetic modification (PSM), defects or solid solutions. 3 rd generation materials or porous flexible MOMs, have attracted attention owing to their potential applications in gas storage, separation, drug delivery and catalysis. These flexible MOMs tend to exhibit ‘stepped’ or ‘S-shaped’ isotherm profiles. Herein, we propose classification of such MOMs based on their gas sorption isotherm profiles as follows, i) type F-I (gradual change from open to more open, ii) type F-II (sudden change from open to more open sudden), iii) type F-III (gradual change from closed to open gradual), iv) type F-IV(sudden change from closed to open) and v) type F-V (shape-memory effect). This thesis also examines the three types of network topologies, primitive cubic unit (pcu), diamondiod (dia) and square lattice (sql) networks. The systematic studies we conducted herein offer design principles for future studies of porous flexible coordination networks in terms of understanding their structural transformations and improving the performance of gas storage/separation.
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