Mode of adsorption of (CH ₃) ₂Au(acac) onto partially dehydroxylated silica

The deposition of volatile cis-(CH ₃) ₂Au((O, O'-acac) onto silica partially dehydroxylated at 400 °C leads to molecular dispersion of the organogold complex. X-ray absorption near-edge structure demonstrates that the gold retains its oxidation state upon binding. IR and ¹H magic-angle spinning NMR spectra suggest that the molecular framework also remains intact. Computational models involving hydroxyl-terminated octasilses-quioxane cube clusters to represent silica predict the most energetically favorable interaction to be hydrogen-bonding between two surface hydroxyls and the oxygen donor atoms of the chelated acetylacetonate ligand. This mode of adsorption was confirmed by analysis of the IR and the Au L _III edge extended X-ray absorption fine structure. The surface hydroxyls most likely to participate in the attachment of the gold complex to silica are vicinal silanol pairs that are not involved in hydrogen bonding to other silanols.