One‐Pot Synthesis of Phenylmethanethiolate‐Protected Au₂₀(SR)₁₆ and Au₂₄(SR)₂₀ Nanoclusters and Insight into the Kinetic Control

Abstract

We report two synthetic routes for concurrent formation of phenylmethanethiolate (-SCH2Ph)-protected Au20(SR)16 and Au24(SR)24 nanoclusters in one-pot by kinetic control. Unlike the previously reported methods for thiolate-protected gold nanoclusters, which typically involve rapid reduction of the gold precursor by excess NaBH4 and subsequent size focusing into atomically monodisperse clusters of a specific size, the present work reveals some insight into the kinetic control in gold-thiolate cluster synthesis. We demonstrate that the synthesis of -SCH2Ph-protected Au20 and Au24 nanoclusters can be obtained through two different, kinetically controlled methods. Specifically, route 1 employs slow addition of a relatively large amount of NaBH4 under slow stirring of the reaction mixture, while route 2 employs rapid addition of a small amount of NaBH4 under rapid stirring of the reaction mixture. At first glance, these two methods apparently possess quite different reaction kinetics, but interestingly they give rise to exactly the same product (i.e., the coproduction of Au20(SCH2Ph)16 and Au24(SCH2Ph)20 clusters). Our results explicitly demonstrate the complex interplay between the kinetic factors that include the addition speed and amount of NaBH4 solution as well as the stirring speed of the reaction mixture. Such insight is important for devising synthetic routes for different sized nanoclusters. We also compared the photoluminescence and electrochemical properties of PhCH2S-protected Au20 and Au24 nanoclusters with the PhC2H4S-protected counterparts. A surprising 2.5 times photoluminescence enhancement was observed for the PhCH2S-capped nanoclusters when compared to the PhC2H4S-capped analogues, thereby indicating a drastic effect of the ligand that is merely one carbon shorter.

Atomically precise metal nanoclusters: stable sizes and optical properties

“…This 20-gold-atom cluster was not in the series of Au n (SG) m clusters reported in the classic work by Negishi et al 16 Zhu et al first observed this size in a size-controlled synthesis of phenylethylthiolate-protected gold nanoclusters in 2009. 42 The Au 20 (SC 2 H 4 Ph) 16 synthesis was done by a kinetically controlled method; specifically, the Au(III) reduction to Au(I) by excess thiol and the subsequent aggregation of Au(I) to the [Au (I) 43 The Au 20 (SR) 16 cluster is charge neutral. The optical absorption spectrum of Au 20 (SC 2 H 4 Ph) 16 shows a distinct band at ∼ 485 nm and a weak band at ∼420 nm, as shown in Fig.…”

Facile synthesis of Au23(SC(CH3)3)16 clusters

“…39 Similar quasi/irreversible electrochemical behaviour has been reported for Au 20 (SC 2 H 4 Ph) 16 and Au 24 (SC 2 H 4 Ph) 20 clusters, with generally a broad peak at $À1.0 V vs. Ag/AgCl. 59 One can conclude that the electronic (and even crystal) structures of Au 20 , Au 23 and Au 24 are similar in terms of the origin of the HOMO and LUMO orbital locations and properties. Further optical properties were investigated using photoluminescence (PL) spectrometry.…”

Ligand Design in Ligand‐Protected Gold Nanoclusters

“…[ 104 ] This method can be further modified to achieve Au NC synthesis in one phase, using a polar solvent like tetrahydrofuran (THF) and methanol. [ 4 ] A wide range of hydrophobic thiolate ligands can be used in this method, and some successful examples are Au 24 (SCH 2 Ph) 20 , [ 54 ] Au 44 (TBBT) 28 (TBBT = 4‐tert‐butylbenzenethiolate), [ 77 ] Au 64 (S‐ c ‐C 6 H 11 ) 32 (S‐ c ‐C 6 H 11 = cyclohexanethiolate), [ 105 ] and Au 25 (SC 2 H 4 Ph) 18. [ 106 ] The reaction conditions, such as temperature and stirring rate, can also be used to further control the reaction kinetics to synthesize different sized Au NCs.…”