Toward an Atomic-Level Understanding of Size-Specific Properties of Protected and Stabilized Gold Clusters

Abstract

Metal clusters consisting of fewer than 100 atoms (diameter <2 nm) are highly promising as a new class of building units for functional materials because of their novel and size-dependent properties. Nevertheless, basic and applied studies of metals clusters have been hampered by the lack of specific guidelines for design and precise synthetic methods. This account surveys recent investigations of gold clusters focusing on our effort toward an atomic-level understanding and control of their size-specific properties. We have developed a size-controlled method for synthesizing gold clusters protected by ligands, stabilized by polymers, and supported on solids. Remarkable size-effects on stabilities and various properties including catalysis were observed. Their mechanisms are discussed based on fundamental knowledge of bare gold clusters in the gas phase.

All-thiol-stabilized Ag44 and Au12Ag32 nanoparticles with single-crystal structures

“…In contrast to such a coordination configuration, we find here that the surface layer of the [M 12 Ag 32 (SR) 30 ] 4 À cluster consists of six three-dimensional Ag 2 (SR) 5 units in which Ag cations bind to three thiolate ligands in a planar Ag(SR) 3 configuration. The five thiolate ligands in each surface Ag 2 (SR) 5 motif are classified into two groups. Although the four thiolates directly bonded to the Ag atoms on the M 12 @Ag 20 core are threefold coordinated, the one thiolate jointing the outmost Ag(I) cations is twofold coordinated.…”

“…As shown in Fig. 1d, the two Ag atoms on the edge of the dodecahedron and the two Ag atoms in each Ag 2 (SR) 5 30 ] 4 À is a completely different binding geometry of surface thiolates as compared with the well-known RS(M-SR-) x , (x ¼ 1, 2) oligomeric unit found in thiolated Au nanoclusters and in self-assembled monolayers of thiolates on Au(111). 13 At the surface of the thiolate-capped Au clusters, Au(I) cations are linearly coordinated to two thiolate ligands that are also bound to two core Au atoms ( Supplementary Fig.…”

“…[1][2][3][4][5][6][7][8][9][10] Size, composition and surface structure are important factors determining the physical, chemical and biological properties of monolayerprotected noble metal nanoparticles. 4,11,12 To achieve chemical fine-tuning, understanding of their structures at the molecular level is crucial.…”

“…[22][23][24][25][26][27][28][29][30][31][32][33] Here we report on the first successful crystal structure determination and theoretical analysis of six all-thiol-protected silver and silver-gold intermetallic nanoparticles, namely three Ag 44 (SR) 30 and three Au 12 Ag 32 (SR) 30 nanoclusters stabilized with fluorinated arylthiols (SR ¼ SPhF, SPhF 2 or SPhCF 3 ). The metal core forms a Keplerate solid of concentric icosahedral and dodecahedral atom shells, protected by six Ag 2 (SR) 5 units in octahedral geometry. The crystal unit cell includes positive counterions indicating a high negative charge of 4 À per nanocluster, and density functional theory (DFT) calculations confirm the expected electronic structure with an 18-electron superatom shell closure in the metal core.…”

“…Each of the six Ag 2 (SR) 5 units is connected to an edge of the Ag 20 pentagonal dodecahedron through Ag-SR interactions. The six edges connected to Ag 2 (SR) 5 units have an octahedral symmetry implicit in the Ag 20 pentagonal dodecahedron. As shown in Fig.…”