Ligand Structure Determines Nanoparticles' Atomic Structure, Metal-Ligand Interface and Properties

Abstract

The nature of the ligands dictates the composition, molecular formulae, atomic structure and the physical properties of thiolate protected gold nanomolecules, Aun(SR)m. In this review, we describe the ligand effect for three classes of thiols namely, aliphatic, AL or aliphatic-like, aromatic, AR, or bulky, BU thiol ligands. The ligand effect is demonstrated using three experimental setups namely: (1) The nanomolecule series obtained by direct synthesis using AL, AR, and BU ligands; (2) Molecular conversion and interconversion between Au38(S-AL)24, Au36(S-AR)24, and Au30(S-BU)18 nanomolecules; and (3) Synthesis of Au38, Au36, and Au30 nanomolecules from one precursor Aun(S-glutathione)m upon reacting with AL, AR, and BU ligands. These nanomolecules possess unique geometric core structure, metal-ligand staple interface, optical and electrochemical properties. The results unequivocally demonstrate that the ligand structure determines the nanomolecules' atomic structure, metal-ligand interface and properties. The direct synthesis approach reveals that AL, AR, and BU ligands form nanomolecules with unique atomic structure and composition. Similarly, the nature of the ligand plays a pivotal role and has a significant impact on the passivated systems such as metal nanoparticles, quantum dots, magnetic nanoparticles and self-assembled monolayers (SAMs). Computational analysis demonstrates and predicts the thermodynamic stability of gold nanomolecules and the importance of ligand-ligand interactions that clearly stands out as a determining factor, especially for species with AL ligands such as Au38(S-AL)24.

Elucidating ligand effects in thiolate-protected metal clusters using Au24Pt(TBBT)18 as a model cluster

“…1(a)). 28,29,[43][44][45][46] In this work, we have succeeded in preventing the deformation of the framework structure by using cluster 1, which has a strong metal framework, as a precursor cluster.…”

“…Because of this difference in pK a , in cluster 2, the Au-S bond is thought to be weaker than in cluster 1 and the Au 2 (SR) 3 staple is distant from the metal core. 29 Electronic structure. The following has come to light from previous studies for Au 24 Pt(SR) 18 (SR = PET or 1-hexanethiolate (C6)): (i) as for Au 24 Pt(SR) 18 , the total number of valence electrons of the cluster satisfies the closed-shell electron structure as a divalent negative ion ([Au 24 Pt(SR) 18 ] 2− ), and in this [Au 24 Pt(SR) 18 ] 2− , the energy of the highest occupied molecular orbital (HOMO) is triply degenerated (left side in Fig.…”

“…5 In the study of Au n (SR) m clusters, when 2-phenylethanethiolate (PET; Scheme S1(a) †) or 4-tert-butylbenzenethiolate (TBBT; Scheme S1(b) †) is used as a ligand, the single crystallization of clusters is relatively easy and the determination of the geometrical structure of Au n (SR) m clusters is possible by singlecrystal X-ray diffraction analysis (SCXRD). 28,29 Therefore, to understand the correlation between the chemical composition and geometrical structure and that between geometrical structure and physical properties, PET and TBBT have been the two most commonly used ligands in the study of Au n (SR) m clusters. Because these SRs have substantially different functional groups (Scheme S1 †), the resulting Au n (SR) m clusters have different chemical compositions and geometrical structures.…”

“…Because these SRs have substantially different functional groups (Scheme S1 †), the resulting Au n (SR) m clusters have different chemical compositions and geometrical structures. 28,29 For example, when PET is used as the ligand, Au n (PET) m clusters, such as [Au 25 (PET) 18 ] − , [Au 38 (PET) 24 ] 0 , [Au 52 (PET) 32 ] 0 , [Au 144 (PET) 60 ] 0 , and [Au 329 (PET) 84 ] 0 , are formed, whereas, in the case of TBBT, Au n (TBBT) m clusters, such as [Au 28 (TBBT) 20 ] 0 , [Au 36 (TBBT) 24 ] 0 , [Au 52 (TBBT) 32 ] 0 , [Au 133 (TBBT) 52 ] 0 , and [Au 279 (TBBT) 84 ] 0 , are generated. The numbers of gold atoms and ligands are the same in [Au 52 (PET) 32 ] 0 and [Au 52 (TBBT) 32 ] 0 , but their framework structures are significantly different.…”

“…In addition to the chemical composition of the cluster, the stability, electronic structure, and functions of Au n (SR) m clusters change depending on the functional-group structure of the ligand. 9,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] For example, it has been demonstrated that properties of Au 25 (SR) 18 , such as the stability in solution, reducibility, dissociation pattern under laser irradiation, quantum yield of photoluminescence, and catalytic activity, along with other properties, differ depending on the functional-group structure of the ligand. Therefore, the selection of the ligand functional group is essential in the functionalization of Au n (SR) m clusters.…”