Nb2O5 and Ta2O5 Thin Films from Polyoxometalate Precursors: A Single Proton Makes a Difference

Thin film materials from water-based, precursors follow the principals of green chemistry, leading to a more sustain-able future in the energy intensive era in which we currently reside. While simple in practice, aqueous metal-oxide chemistry is complex at the molecular level. Here we develop the first water-based formation of Nb2O5 and Ta2O5 thin films; utilizing tetramethylammonium salts of [H2Ta6O19](6-) and [H3Nb6O19](5-),polyoxometalates. Although the clusters are.Structurally identical group V analogues and differ only by a Single proton, this difference has a considerable influence on the quality of films that are obtained. Through characterization of the solid-state precursor (single-crystal X-ray diffraction), the aqueous precursor solution (X-ray scattering), and the thin films (atomic force and scanning electron microscopies, X-ray diffraction; and reflectivity), we rationalize the important roles of cluster protonation that carry through all chemical processes from the precursor to the metal oxide coating.