Layer-by-Layer Deposition of Rh(I) Diisocyanide Coordination Polymers on Au(111) and Their Chemical and Electrochemical Stability

The synthesis of electrode-attached Rh(I) diisocyanide coordination polymers that incorporate a series of arylene diisocyanide linkers and which are grown from gold surfaces by a bottom-up, layer-by-layer procedure that allows for a high level of control for the film thickness is reported. A seed layer of the arylene diisocyanide ligand is used to template directional growth of the coordination polymer made using the well-studied square-planar rhodium tetrakis(isocyanide) as the metal node. Materials ranging from 1 to 30 layers were prepared via layer-by-layer solution-phase deposition. Characterization of the polymer films using scanning electron microscopy and ellipsometry shows layer-by-layer control in these films with linear thickness growth per layer. Phase-modulated infrared reflection absorption spectroscopy (PM-IRRAS), diffuse reflectance UV-vis, and X-ray photoelectron spectroscopy (XPS) were used to confirm the structures of the films. Although prior reports of related coordination polymers and films based on diisocyanides showed considerable air-instability, the films reported here demonstrate significantly improved chemical stability and electrochemical stability at a moderately high applied bias. Electrochemical characterization and ex situ XPS demonstrate that these diisocyanide films are stable to stripping at potentials up to -2.2 V versus decamethylferrocene in acetonitrile, supporting their relevance for electrochemical applications.