Crystals versus Electrochromic Films: Pathway-Dependent Coordination Networks

We demonstrate the formation of metal-organic frameworks (MOFs) and thin-film coatings that have entirely different compositions and structures, distinct by cation exchange, despite using the same set of starting materials. The reaction of an iron polypyridyl complex with a copper salt by diffusion of one solution into another resulted in iron-to-copper exchange, concurrent ligand rearrangement and the formation of MOFs. This observation shows that polypyridyl complexes can be used as expendable precursors for the growth of MOFs. In contrast, alternative depositions of the iron polypyridyl complex with a copper salt by automated spin-coating on conductive metal-oxides resulted in the formation of electrochromic coatings, and the structure and redox properties of the iron complex were retained. The possibility to form such different networks by “in solution” versus "on surface” coordination chemistry from the same set of molecular building blocks broadens the synthetic space to design functional materials.