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 alpha-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 alpha-K9AlW11O39 (K(9)1) and alpha-Na5AlW12O40 (Na(5)2) 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. (C) 2010 Elsevier B.V. All rights reserved.