Reentrant Gel-Sol-Gel transition of a lipophilic Co(II) coordination polymer

A reentrant gel-sol-gel phase transition in organic media is achieved for a single-component, thermoresponsive Co(II)-based coordination polymer bridged by suitably designed lipophilic 1,2,4-triazole ligands. Its green chloroform solution at room temperature turns into a blue gel upon heating, whereas it is transformed to a yellow gel by cooling. These unique thermal phase transitions are reversible and occur all by themselves, which originate from the simultaneous pursuit of entropy-driven changes in coordination structures and enthalpydriven interactions between the coordination polymers.