Synthetic and Postsynthetic Chemistry of M₄Au_xAg_44–x(p-MBA)₃₀Alloy Nanoparticles

Abstract

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 M4Au x Ag44–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 M4Au x Ag44–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 M4Au x Ag44–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 M4Au x Ag(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.

The stability enhancement factor beyond eight-electron shell closure in thiacalix[4]arene-protected silver clusters

“…Our theoretical calculation also demonstrates that the interaction energy between the central atom and the Ag 12 shell in 2 is larger than that in 1 (Table S1†). In addition, electrophilicity of gold atoms is also accountable for the stabilization of heteronuclear nanoclusters 38…”

Atomically Precise Alloy Nanoclusters

“…[56,57] This illustrates that [Ag 44 [57] The groups of Xie, Pradeep, and Kappes, and Bigioni independently reported the synthesis of [Ag 44Àx Au x (SR) 30 ] 4À alloy NCs (n = 0-12;S R = p-MBA or SPhF). [89,102,195] In the same paper,X ie et al [89] also reportedt he synthesis of [Ag 44Àx Cu x (p-MBA) 30 ] 4À alloy NCs (x = 0-6). .…”

M4Au12Ag32(p-MBA)30(M= Na, Cs) bimetallic monolayer-protected clusters: synthesis and structure

“…Silver and gold mix readily to form the naturally occurring alloy electrum and therefore the study of mixtures of silver and gold within these MPCs is of interest (Yang et al, 2013). Mixtures of M 4 Au x Ag 44-x (p-MBA) 30 MPCs can be obtained by co-reducing silver and gold polymers of p-MBA, where 0 x 12 (Conn et al, 2018). Gold-rich species have been synthesized and then thermally processed to destroy the species that contained fewer gold atoms, thereby enriching the samples in M 4 Au 12 Ag 32 (p-MBA) 30 MPCs.…”

“…Furthermore, gold is known to be more electronegative and more noble than silver, so the gold atoms are expected to assume positions within the structure where they can possess the lowest oxidation state among the metal atoms. Bader analysis (Bader, 1990;Tang et al, 2009) of the electron distribution in M 4 Ag 44 (p-MBA) 30 has shown that atoms in the inner icosahedral core have an oxidation state of zero (Conn et al, 2015;Yang et al, 2013) whereas in M 4 Au 12 Ag 32 (p-MBA) 30 those atoms are slightly reduced (Conn et al, 2018). The other metal atoms were found to be oxidized, with their oxidation states increasing with distance from the center of the molecule.…”