Gold Nanomaterials

Abstract

The strong development of activities related to the nanoscience and nanotechnology of gold has led to a great number of publications in this research field. In this chapter, we will focus on the synthesis of cluster aggregates displaying gold-gold bonds and the formation of gold nanoparticles. Special consideration will be given to the chemical bottom-up approach for the synthesis of gold nanomaterials using different methods.Section 3.2 describes the synthesis and structure of small gold clusters taking into account the number of gold atoms, the reducing agents employed and the stabilizing ligands used, such as phosphines, arsines, thiols, and so on. Section 3.3 discusses the synthesis and properties of large size gold clusters such as the Au 55 cluster series. Finally, in Section 3.4, we describe the synthesis of gold nanoparticles and the development of new nanomaterials based on gold nanoparticles using bottom-up chemical methods and give a short summary of their properties and applications. Molecular Gold ClustersHerein we describe the synthesis and characterization of small-size homonuclear gold cluster compounds with a nuclearity ranging from 3 to 39 gold atoms. These types of clusters are usually characterized through definitive structural techniques such as single-crystal X-ray diffraction, enabling in-depth study of the structural arrangements found in the solid state.This section is divided into two main subsections. The first describes the synthesis and characterization of phosphine-stabilized gold clusters. The second focuses on the synthesis and characterization of thiol-stabilized gold clusters and the study of other stabilizers such as arsines or boranes are described.The first tetranuclear gold clusters were reported in the 1980s, namely [Au 4 (PPh 3 ) 4 (m-I) 2 ] (Au-Au distances from 2.649(1) to 2.828(1) Å) [1] and [Au 4 (dppm) 3 (m 3 -I)I] (Au-Au distances from 2.724(1) to 2.947(1) Å) [2]. The first cluster was prepared through a degradation reaction of the nonanuclear cluster [Au 9 (PPh 3 ) 8 ] 3þ , while the second was obtained by reaction of the already mentioned [Au 4 (PPh 3 ) 4 (m-I) 2 ] cluster and one equivalent of dppm ligand. Both structures display distorted tetrahedral cores of gold atoms with the iodine atoms bridging two different gold centers in the first case and three gold centers in the second (Scheme 3.1).In the 1990s, tetranuclear gold clusters [Au 4 (PR 3 ) 4 ]BF 4 (R ¼ t Bu [3] and (C 6 H 3 Me-1,3,5) [4]) were reported. Both clusters are synthesized from the corresponding oxonium salts [O{Au(PR 3 )] 3 ]BF 4 and [HO{Au(PR 3 )] 2 ]BF 4 (R ¼ t Bu and (C 6 H 3 Me-1,3,5)). In both clusters, X-ray diffraction analysis showed that gold atoms form a regular tetrahedron and each phosphine ligand is coordinated to one gold center (Scheme 3.2).The latest examples of tetranuclear gold clusters are based on phosphinocarborane ligands, namely [Au 4 {(PPh 2 ) 2 C 2 B 9 H 10 } 2 {P(4-OMeC 6 H 4 ) 3 } 2 ] [5] and, more recently, [Au 4 {(PPh 2 ) 2 C 2 B 9 H 10 } 2 {PPh 3 } 2 ] [6]. The firs...

Electronic Properties of [Core+exo]-type Gold Clusters: Factors Affecting the Unique Optical Transitions

“…Single-crystal X-ray analyses provide precise structural information, thus being most useful for elucidating the relationship between the geometry and the optical properties of ultrasmall molecular clusters. The molecular structures of numerous phosphine- and thiolate-coordinated gold clusters with well-defined nuclearity, which form major families in cluster chemistry, have been reported. − From a structural standpoint, phosphine-coordinated clusters can be simply partitioned into the inorganic moiety (metal) and surrounding organic ligands (shell) because of the neutral character of phosphine, whereas thiolate-capped clusters are rather complicated because the gold core is covered by a gold–thiolate layer. − Thus, the phosphine-coordinated family offers suitable structural models for studying the nature of the central gold moieties. The crystal structures of monophosphine-coordinated clusters (Au 7 , Au 8 , Au 9 , Au 11 , − Au 13 , ) have indicated that the gold units favor icosahedron-based geometries.…”

Ligand-Based Toolboxes for Tuning of the Optical Properties of Subnanometer Gold Clusters

“…The electronic and optical properties of nanometer-sized gold compounds continue to receive interest in relation to applications in diverse areas including sensing, optoelectronic materials, and catalysis. − It is well-known that conventional colloidal nanoparticles with diameters of several nanometres exhibit visible electronic absorption bands due to the localized surface plasmon. ,− However, when the size is decreased to less than 2 nm, such plasmon resonances disappear, and instead, structured UV–vis absorptions indicative of discrete electronic transitions emerge. − Such molecular-like behaviors are characteristic of small clusters with nuclearity of less than 50, whose sizes reach to the subnanometer regime. Thus, it is now well recognized that small clusters are different from conventional colloidal nanoparticles in terms of electronic structures and properties.…”

Protonation-Induced Chromism of Pyridylethynyl-Appended [core+exo]-Type Au8 Clusters. Resonance-Coupled Electronic Perturbation through π-Conjugated Group

“…The interaction between gold and CC π systems continues to be of interest because it has a number of versatile applications. − Simple complexes of gold(I) and gold(III) have been extensively studied with regard to their unique photoluminescence (PL) ,− as well as their crucial role in some catalytic organic reactions. − However, although phosphine- and thiolate-capped gold clusters and nanoparticles have been well characterized, − examples of alkyne (alkynyl)-modified clusters/nanoparticles are quite rare , and so the potential interactions between CC π systems and a gold kernel have been left unexplored. Herein we report the first phosphine-coordinated molecular gold clusters having alkynyl substituents ( 2 – 6 ).…”