Layer-by-Layer Deposition of Rh(I) Diisocyanide Coordination Polymers on Au(111) and Their Chemical and Electrochemical Stability
Gwendolynne L. Lee, Thomas Chan, Joseph M. Palasz, Clifford P. Kubiak
Abstract
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.