Platinum nanoparticles stabilized by CO and octanethiol ligands or polymers: FT-IR, NMR, HREM and WAXS studies

The reaction of Pt-2(dba)(3) with CO leads rapidly to the formation of platinum nanoparticles. Stabilization of the particles was achieved by octanethiol or various polymers. Spectroscopic studies demonstrate the coordination of thiol at the surface of the particles. The size distribution is quasi monodisperse and centered near 1.6 +/- 0.15 nm as demonstrated by HREM. However, only the core of the particles is crystalline, the outer shell being heavily disordered as demonstrated both by HREM and WAXS. This disorder is attributed to the influence of strongly coordinating ligands. For comparison, HREM and WAXS data were recorded on platinum nanoparticles prepared in various polymers: polyvinylpyrrolidone (PVP), nitrocellulose (NC) and cellulose acetate (CA). In addition, a sample has been obtained from decomposition of Pt-2(dba)(3) by dihydrogen in PVP. The particles are well-crystallized and display HREM sizes that vary as a function of the polymer: <1 nm (PVP/CO), 1.30 +/- 0.15 nm (NC), 1.70 +/- 0.15 nm (CA) and 1.50 +/- 0.15 nm (PVP/H-2). Models elaborated from WAXS data recorded on these different colloids are in agreement with the presence of, respectively, one-shell clusters, a mixture of two- and three-shell clusters (85 : 15), a mixture of three- and four-shell clusters (80 : 20) and three-shell clusters. There is little or no discrepancy between the HREM and WAXS data in these cases, hence demonstrating the absence of strong interactions between the polymers and the surface. The best fit was obtained for the colloid prepared under H-2 in PVP, which resembles a free platinum nanoparticle, whereas the colloid stabilized by thiol(ate) ligands behaves as a 'giant cluster'.