Reversible binding of an inorganic cluster-anion to the surface of a gold nanoparticle

Reversible dissociation of POM ligands from electrostatically stabilized monolayer assemblies on metal(0)-nanoparticle surfaces would provide substrates with direct access to reactive metal(0) lattices. As a result, POM-ligand lability could play an important role in catalysis by POM-monolayer protected metal(0) nanoparticles. POM-ligand lability was addressed by first obtained cryogenic transmission electron microscopy (cryo-TEM) images of monolayers of α-AlW11O399- on a 5.4 nm diameter gold-core nanoparticle. These are the smallest nanoparticles on which POM monolayers have been imaged by cryo-TEM. The binding affinities of α-K9AlW11O39α-K9AlW11O39 (K91) and α-Na5AlW12O40α-Na5AlW12O40 (Na52) were obtained from Langmuir isotherms, and the relative labilities of the two ligands were assessed by UV–Vis analysis of changes in surface plasmon resonance (SPR) upon incremental additions of citrate. Thermodynamic constants, K, for monolayer formation by 1 and 2 are 20,000 and 150 M−1, respectively. In timed reactions with citrate, 1 exhibits a substantial kinetic barrier to dissociation, while 2 is rapidly exchanged by the organic protecting ligand.

Graphical abstractCryogenic transmission electron microscopy (cryo-TEM) reveals monolayers of α-AlW11O399- (1) on a 5 nm gold-core nanoparticle. UV–Vis spectroscopic analysis of changes in the surface plasmon resonance (SPR) are then used to assess the relative binding constants and labilities of 1 and of the less highly charged protecting anion, α-AlW12O405- (2).Figure optionsDownload full-size imageDownload as PowerPoint slide