title: Balancing the rate of cluster growth and etching for gram-scale synthesis of thiolate-protected Au(25) nanoclusters with atomic precision.
abstract: We report a NaOH-mediated NaBH4 reduction method for the synthesis of mono-, bi-, and tri-thiolate-protected Au25 nanoclusters (NCs) with precise control of both the Au core and thiolate ligand surface. The key strategy is to use NaOH to tune the formation kinetics of Au NCs, i.e., reduce the reduction ability of NaBH4 and accelerate the etching ability of free thiolate ligands, leading to a well-balanced reversible reaction for rapid formation of thermodynamically favorable Au25 NCs. This protocol is facile, rapid (≤3 h), versatile (applicable for various thiolate ligands), and highly scalable (>1 g Au NCs). In addition, bi- and tri-thiolate-protected Au25 NCs with adjustable ratios of hetero-thiolate ligands were easily obtained. Such ligand precision in molecular ratios, spatial distribution and uniformity resulted in richly diverse surface landscapes on the Au NCs consisting of multiple functional groups such as carboxyl, amine, and hydroxy. Analysis based on NMR spectroscopy revealed that the hetero-ligands on the NCs are well distributed with no ligand segregation. The unprecedented synthesis of multi-thiolate-protected Au25 NCs may further promote the practical applications of functional metal NCs.
authors.affiliation: Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585 (Singapore).
authors.forename: Xun
authors.initials: X
authors.lastname: Yuan
authors.forename: Bin
authors.initials: B
authors.lastname: Zhang
authors.forename: Zhentao
authors.initials: Z
authors.lastname: Luo
authors.forename: Qiaofeng
authors.initials: Q
authors.lastname: Yao
authors.forename: David Tai
authors.initials: DT
authors.lastname: Leong
authors.forename: Ning
authors.initials: N
authors.lastname: Yan
authors.forename: Jianping
authors.initials: J
authors.lastname: Xie
keywords: nanoparticles; noble metal clusters; surface chemistry; synthesis (inorg.); thiolate