A New Dimension for Coordination Polymers and Metal-Organic Frameworks: Towards Functional Glasses and Liquids

There are two categories of coordination polymers (CPs): inorganic CPs (i-CPs) and organic ligand bridged CPs (o-CPs). Based on the successful crystal engineering of CPs, we here propose noncrystalline states and functionalities as a new research direction for CPs. Control over the liquid or glassy states in materials is essential to obtain specific properties and functions. Several studies suggest the feasibility of obtaining liquid/glassy states in o-CPs by design principles. The combination of metal ions and organic bridging ligands, together with the liquid/glass phase transformation, offer the possibility to transform o-CPs into ionic liquids and other ionic soft materials. Synchrotron measurements and computational approaches contribute to elucidating the structures and dynamics of the liquid/glassy states of o-CPs. This offers the opportunity to tune the porosity, conductivity, transparency, and other material properties. The unique energy landscape of liquid/glass o-CPs offers opportunities for properties and functions that are complementary to those of the crystalline state.