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The size-dependent influence of palladium doping on the structures of cationic gold clusters† † Electronic supplementary information (ESI) available. See DOI: 10.1039/d1na00587a

ABSTRACT: The physicochemical properties of small metal clusters strongly depend on their precise geometry. Determining such geometries, however, is challenging, particularly for clusters formed by multiple elements. In this work, we combine infrared multiple photon dissociation spectroscopy and density functional theory calculations to investigate the lowest-energy structures of Pd doped gold clusters, PdAun−1+ (n ≤ 10). The high-quality experimental spectra allow for an unambiguous determination of the structures adopted by the clusters. Our results show that the Pd–Au interaction is so large that the structures of PdAun−1+ and Aun+ are very different. Pd doping induces a 2D to 3D transition at much smaller cluster sizes than for pure Aun+ clusters. PdAun−1+ clusters are three-dimensional from n = 4, whereas for Aun+ this transition only takes place at n = 7. Despite the strong Au–Pd interaction, the Aun−1+ cluster geometries remain recognizable in PdAun−1+ up to n = 7. This is particularly clear for PdAu6+. In PdAu8+ and PdAu9+, Pd triggers major rearrangements of the Au clusters, which adopt pyramidal shapes. For PdAu4+ we find a geometry that was not considered in previous studies, and the geometry found for PdAu8+ does not correspond to the lowest-energy structure predicted by DFT, suggesting kinetic trapping during formation. This work demonstrates that even with the continuous improvement of computational methods, unambiguous assignment of cluster geometries still requires a synergistic approach, combining experiment and computational modelling. The physicochemical properties of small metal clusters strongly depend on their precise geometry.

SUBMITTER: Ferrari P

PROVIDER: S-EPMC8548875 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Reducing dilute aqueous HAuCl4 with NaSCN under alkaline conditions produces 2-3 nm diameter yellow nanoparticles without the addition of extraneous capping agents. We here describe two very simple methods for producing highly stable oligomeric grape-like clusters (oligoclusters) of these small nanoparticles. The oligoclusters have well-controlled diameters ranging from ?5 to ?30 nm, depending mainly on the number of subunits in the cluster. Our first ["delay-time"] method controls the size of the oligoclusters by varying from seconds to hours the delay time between making the HAuCl4 alkaline and adding the reducing agent, NaSCN. Our second ["add-on"] method controls size by using yellow nanoparticles as seeds onto which varying amounts of gold derived from "hydroxylated gold", Na(+)[Au(OH4-x)Clx](-), are added-on catalytically in the presence of NaSCN. Possible reaction mechanisms and a simple kinetic model fitting the data are discussed. The crude oligocluster preparations have narrow size distributions, and for most purposes do not require fractionation. The oligoclusters do not aggregate after ?300-fold centrifugal-filter concentration, and at this high concentration are easily derivatized with a variety of thiol-containing reagents. This allows rare or expensive derivatizing reagents to be used economically. Unlike conventional glutathione-capped nanoparticles of comparable gold content, large oligoclusters derivatized with glutathione do not aggregate at high concentrations in phosphate-buffered saline (PBS) or in the circulation when injected into mice. Mice receiving them intravenously show no visible signs of distress. Their sizes can be made small enough to allow their excretion in the urine or large enough to prevent them from crossing capillary basement membranes. They are directly visible in electron micrographs without enhancement, and can model the biological fate of protein-like macromolecules with controlled sizes and charges. The ease of derivatizing the oligoclusters makes them potentially useful for presenting pharmacological agents to different tissues while controlling escape of the reagents from the circulation.

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The size-dependent influence of palladium doping on the structures of cationic gold clusters† † Electronic supplementary information (ESI) available. See DOI: 10.1039/d1na00587a

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