Counterintuitive Adsorption of [PW₁₁O₃₉]^7- on Au(100)

Understanding the interaction between charged species and surfaces is one of the most challenging topics in chemistry, given its wide involvement in several fields such as electrocatalysis, stabilization of metal nanoparticles, preparation of devices, etc. In general, these systems are particularly complex to model because of the elevated number of factors that must be taken into account. Here, we report a robust strategy based on density functional theory for studying these interactions, which has been applied to the highly charged lacunary [PW₁₁O₃₉]^7- (PW₁₁) adsorbed on gold and silver surfaces. In this context, we find that, unlike the modeling of polyoxoanions in solution, the incorporation of counterions in the computational models is crucial for accurately reproducing the properties of the system, even if an implicit solvent is used. Most interestingly, we find that the PW₁₁ cluster does not preferentially adsorb to the gold surface via its more nucleophilic monodefect face but, rather, through less negatively charged terminal oxygen ligands, with an orientation similar to that found for the nondefective Keggin anion [SiW₁₂O₄₀]^4-, induced by the strong anion-cation interactions from the same and neighboring units. This counterintuitive result is important for ongoing efforts to understand and utilize the properties of polyoxometalate monolayers on gold and other reactive metal surfaces.