Urea and thiourea based coordination polymers and metal-organic frameworks: Synthesis, structure and applications

Coordination polymers (CPs) and metal–organic frameworks (MOFs) are commonly constructed by self-assembly of metal ions and multidentate organic linkers and have gained a significant attention in the past two decades. Due to their structural properties, high chemical and thermal stability and tunable pore sizes, they show potential application in different areas, such as gas adsorption and separation, catalysis, sensing, drug delivery, etc. Moreover, their tunability with functional organic ligands is of unquestionably importance due to the limitless possibility of designing various functional organic linkers as well as the particular chemical properties of functional groups. Designing of CPs/MOFs by incorporating different functionalities can be undertaken either via direct synthesis or via modification of ligand or metal centre. Due to the conformational flexibility, strong hydrogen bonding capabilities and polarizability of the urea and thiourea groups, recently a significant attention has been dedicated to developing functionalized CPs/MOFs with such moieties. These functional groups decorated compounds can show not only attractive structures but also a significant improvement in gas adsorption, catalytic and sensing properties. Although this area of research has been developed remarkably in the last few years, it had not yet been reviewed. This review describes recent developments in urea and thiourea functionalized frameworks by discussing their synthesis, structure and applications. It addresses the different synthetic methodologies, followed by their structural description. Lastly, their applications on gas adsorptions and separation, heterogeneous catalytic reactions, and sensing are described. The effects of functional groups on the structure and applications of functionalized materials are also discussed.