A structural model for silicotungstate (α-SiW₁₂O₄₀^4-) monolayers on silver (111)

Self-assembled monolayers of α-SiW₁₂C₄₀^4- anions on Ag(111) surfaces adopt an ordered structure in which approximately square domains of anions separated by 10.2 ± 0.5 Å are misoriented by about 30° relative to each other. An anion-substrate bonding model is proposed where α-SiW₁₂O₄₀^4- anions act as tetradentate ligands bridging four silver surface atoms arranged at the vertices of 2 × √3 rectangle. The anions occupy translationally-equivalent brinding sites on a (4 1 1 4) Ag(111) superlattice whose primitive unit cell is almost square, with a′ = b = √13 a = 10.42 Å and α = 92.2°.