Synthesis of Au₃₈(SCH₂CH₂Ph)₂₄, Au₃₆(SPh‑<i>t</i>Bu)₂₄, and Au₃₀(S‑<i>t</i>Bu)₁₈ Nanomolecules from a Common Precursor Mixture

Phenylethanethiol protected nanomolecules such as Au₂₅, Au₃₈, and Au₁₄₄ are widely studied by a broad range of scientists in the community, owing primarily to the availability of simple synthetic protocols. However, synthetic methods are not available for other ligands, such as aromatic thiol and bulky ligands, impeding progress. Here we report the facile synthesis of three distinct nanomolecules, Au₃₈(SCH₂CH₂Ph)₂₄, Au₃₆(SPh-<i>t</i>Bu)₂₄, and Au₃₀(S-<i>t</i>Bu)₁₈, exclusively, starting from a common Au_<i>n</i>(glutathione)_<i>m</i> (where <i>n</i> and <i>m</i> are number of gold atoms and glutathiolate ligands) starting material upon reaction with HSCH₂CH₂Ph, HSPh-<i>t</i>Bu, and HS<i>t</i>Bu, respectively. The systematic synthetic approach involves two steps: (i) synthesis of kinetically controlled Au_<i>n</i>(glutathione)_<i>m</i> crude nanocluster mixture with 1:4 gold to thiol molar ratio and (ii) thermochemical treatment of the purified nanocluster mixture with excess thiols to obtain thermodynamically stable nanomolecules. Thermochemical reactions with physicochemically different ligands formed highly monodispersed, exclusively three different core-size nanomolecules, suggesting a ligand induced core-size conversion and structural transformation. The purpose of this work is to make available a facile and simple synthetic method for the preparation of Au₃₈(SCH₂CH₂Ph)₂₄, Au₃₆(SPh-<i>t</i>Bu)₂₄, and Au₃₀(S-<i>t</i>Bu)₁₈, to nonspecialists and the broader scientific community. The central idea of simple synthetic method was demonstrated with other ligand systems such as cyclopentanethiol (HSC₅H₉), cyclohexanethiol­(HSC₆H₁₁), <i>para</i>-methylbenzenethiol­(pMBT), 1-pentanethiol­(HSC₅H₁₁), 1-hexanethiol­(HSC₆H₁₃), where Au₃₆(SC₅H₉)₂₄, Au₃₆(SC₆H₁₁)₂₄, Au₃₆(pMBT)₂₄, Au₃₈(SC₅H₁₁)₂₄, and Au₃₈(SC₆H₁₃)₂₄ were obtained, respectively

Core-Size Conversion of Au₃₈(SCH₂CH₂Ph)₂₄ to Au₃₀(S–<i>t</i>Bu)₁₈ Nanomolecules

Au₃₈(SCH₂CH₂Ph)₂₄ nanomolecules upon etching with <i>tert</i>-butylthiol undergo core-size conversion to green-gold Au₃₀(S–<i>t</i>Bu)₁₈ via Au₃₆(SCH₂CH₂Ph)_{24‑<i>x</i>}(S–<i>t</i>Bu)_<i>x</i> intermediate. The structural transformation from Au₃₈ to Au₃₀ indicates a strong steric effect due to the <i>tert</i>-butyl group of the exchanging ligand in contrast to electronic effect by ligands such as thiophenol, which transforms the Au₃₈(SCH₂CH₂Ph)₂₄ to Au₃₆(S–<i>t</i>Bu)₂₄. In this work, fast reaction kinetics were observed and thermodynamically stable Au₃₀(S–<i>t</i>Bu)₁₈ was obtained in molecular purity

Organosoluble Au₁₀₂(SPh)₄₄ Nanomolecules: Synthesis, Isolation, Compositional Assignment, Core Conversion, Optical Spectroscopy, Electrochemistry, and Theoretical Analysis

Characterization of <i>p</i>-mercaptobenzoic acid (p-MBA) protected Au₁₀₂(p-MBA)₄₄ nanomolecules has been so far limited by its water-soluble ligand system. In this work we report the first synthesis and isolation of thiolate-protected organosoluble Au₁₀₂(SPh-X)₄₄ nanomolecules via one-phase synthesis. Monodispersity of the nanomolecules was confirmed from matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), and composition was determined from high-resolution electrospray ionization mass spectrometry (ESI-MS). For the first time we report the electrochemical behavior and temperature-dependent optical spectra of Au₁₀₂(SPh)₄₄. Theoretical simulations on the titled nanomolecules fully validate experimental data and demonstrate the role of electronic conjugation on optical properties

Data_Sheet_1_Ligand Structure Determines Nanoparticles' Atomic Structure, Metal-Ligand Interface and Properties.PDF

<p>The nature of the ligands dictates the composition, molecular formulae, atomic structure and the physical properties of thiolate protected gold nanomolecules, Au_n(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 Au_n(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.</p

Au₃₈(SPh)₂₄: Au₃₈ Protected with Aromatic Thiolate Ligands

Au₃₈(SR)₂₄ is one of the most extensively investigated gold nanomolecules along with Au₂₅(SR)₁₈ and Au₁₄₄(SR)₆₀. However, so far it has only been prepared using aliphatic-like ligands, where <i>R</i> = −SC₆H₁₃, −SC₁₂H₂₅ and −SCH₂CH₂Ph. Au₃₈(SCH₂CH₂Ph)₂₄ when reacted with HSPh undergoes core-size conversion to Au₃₆(SPh)₂₄, and existing literature suggests that Au₃₈(SPh)₂₄ cannot be synthesized. Here, contrary to prevailing knowledge, we demonstrate that Au₃₈(SPh)₂₄ can be prepared if the ligand exchanged conditions are optimized, under delicate conditions, without any formation of Au₃₆(SPh)₂₄. Conclusive evidence is presented in the form of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), electrospray ionization mass spectra (ESI-MS) characterization, and optical spectra of Au₃₈(SPh)₂₄ in a solid glass form showing distinct differences from that of Au₃₈(S-aliphatic)₂₄. Theoretical analysis confirms experimental assignment of the optical spectrum and shows that the stability of Au₃₈(SPh)₂₄ is not negligible with respect to that of its aliphatic analogous, and contains a significant component of ligand−ligand attractive interactions. Thus, while Au₃₈(SPh)₂₄ is stable at RT, it converts to Au₃₆(SPh)₂₄ either on prolonged etching (longer than 2 hours) at RT or when etched at 80 °C

Crystal Structure and Theoretical Analysis of Green Gold Au₃₀(S‑<i>t</i>Bu)₁₈ Nanomolecules and Their Relation to Au₃₀S(S‑<i>t</i>Bu)₁₈

We report the complete X-ray crystallographic structure as determined through single-crystal X-ray diffraction and a thorough theoretical analysis of the green gold Au₃₀(S-<i>t</i>Bu)₁₈. While the structure of Au₃₀S­(S-<i>t</i>Bu)₁₈ with 19 sulfur atoms has been reported, the crystal structure of Au₃₀(S-<i>t</i>Bu)₁₈ without the μ₃-sulfur has remained elusive until now, though matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS) data unequivocally show its presence in abundance. The Au₃₀(S-<i>t</i>Bu)₁₈ nanomolecule not only is distinct in its crystal structure but also has unique temperature-dependent optical properties. Structure determination allows a rigorous comparison and an excellent agreement with theoretical predictions of structure, stability, and optical response

Crystal Structure and Theoretical Analysis of Green Gold Au₃₀(S‑<i>t</i>Bu)₁₈ Nanomolecules and Their Relation to Au₃₀S(S‑<i>t</i>Bu)₁₈

We report the complete X-ray crystallographic structure as determined through single-crystal X-ray diffraction and a thorough theoretical analysis of the green gold Au₃₀(S-<i>t</i>Bu)₁₈. While the structure of Au₃₀S­(S-<i>t</i>Bu)₁₈ with 19 sulfur atoms has been reported, the crystal structure of Au₃₀(S-<i>t</i>Bu)₁₈ without the μ₃-sulfur has remained elusive until now, though matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS) data unequivocally show its presence in abundance. The Au₃₀(S-<i>t</i>Bu)₁₈ nanomolecule not only is distinct in its crystal structure but also has unique temperature-dependent optical properties. Structure determination allows a rigorous comparison and an excellent agreement with theoretical predictions of structure, stability, and optical response