Synthetic and Postsynthetic Chemistry of M4AuxAg44–x(p‑MBA)30 Alloy Nanoparticles
journal contributionposted on 29.05.2018, 00:00 by Brian E. Conn, Aydar Atnagulov, Badri Bhattarai, Bokwon Yoon, Uzi Landman, Terry P. Bigioni
Metal heteroatom substitution in molecular nanoparticles offers a unique opportunity to study alloying with an unprecedented level of detail and control, which may be important for applications in optics, electronics, medicine, and catalysis. Many examples of single- or few-heteroatom substitutions exist in molecular nanoparticles, but true alloys with compositions varying over a wide range of substitutions are rare. Here, we study M4AuxAg44–x(p-MBA)30 alloy nanoparticles as a model system, where M is a countercation and p-MBA is a p-mercaptobenzoic acid ligand, and where 0 ≤ x ≤ 12 represents the full range of possible compositions, all of which are stable in solution. Synthetic reactions produced M4AuxAg44–x(p-MBA)30 alloy nanoparticle products whose compositions were found to be a complex function of the reaction mixture composition. Postsynthetic reactions showed that oxidation of M4AuxAg44–x(p-MBA)30 nanoparticles was slowed in a monotonic fashion by the addition of gold atoms. Density functional theory provided insights into the variation in the chemistry, electronic structure, and reactivity of M4AuxAg(44–x)(p-MBA)30 nanoparticle alloys as a function of composition and showed that the stabilization mechanism was the result of the electrophilicity of the gold atoms, which polarized the metal core. An oxidation reaction mechanism was proposed based on these experimental and computational results, which involved the octahedrally located silver atoms.