Syntheses of mono and bimetallic cyamelurate polymers with reversible chromic behaviour

Ordered coordination polymers (CPs) have been an interesting class of materials for scientific and industrial research for the last few decades. However, their availability as well as certain economic and environmental limitations could slow down their use in many applications. Herein, we present room temperature synthesis in water of a series of CPs (four metal-organic polymers MOPs-(1-4) and three mixed metal-organic polymers MMOPs-(5-7)). All MMOPs were found to be isostructural to MOPs as determined by XRD. Remarkably, MOPs-(2 and 3) and MMOPs-(5-7) exhibit switchable chromic behaviour associated with reversible structural transformation which was facilitated by dehydration/rehydration or solvent exchange (MeOH/H₂O) processes. Chromic behaviour and its mechanism were investigated using IR, solid-state UV-Vis, XRD, PXRD and TGA indicating the coordination/de-coordination of water molecules to be the key factor that influences the colour changes. These results render the potential application of MOPs and MMOPs as sensor materials.