Structure-property relationships on thiolate-protected gold nanoclusters

A theoretical study of the monolayer-protected gold cluster Au317(SR)110

Significant efforts have been made to uncover the structures of monolayer-protected gold nanoclusters. However, the synthesis, crystallization, and structural analysis of gold nanoclusters with over 300 metal atoms is a grand challenge. In this work, a new gold nanocluster containing 317 gold atoms and 110 thiolate (SH) ligands (referred to as Au₃₁₇(SH)₁₁₀) is theoretically studied, which is larger in size than the formerly reported Au₂₇₉(SR)₈₄ cluster. The stability of the Au₃₁₇(SH)₁₁₀ cluster is studied based on calculations of the averaged cluster formation energy (E_ave), indicating that Au₃₁₇(SH)₁₁₀ has good structural stability and that the SPhCOOH (p-MBA) ligand is a good candidate for stabilizing the cluster. The calculation of density of state and the time-dependent density functional theory (TD-DFT) calculations of the optical absorption properties show that Au₃₁₇(SH)₁₁₀ is in a metallic state.

Origin of the structural stability of cage-like Au144 clusters

Cage-like metal nanoclusters are rarely found due to the densely packed property of metals. Recently, single crystallography has unraveled for the first time that multi-shell golden cages are formed in large-size thiolate (SR) and alkynl (CCR) protected neutral Au₁₄₄ nanoclusters, denoted as Au₁₄₄(SR)₆₀ and Au₁₄₄(CCR)₆₀. In this study, the origin of the structural stability of golden cage Au₁₄₄ clusters is studied based on the density functional theory (DFT) energy calculation and energy decomposition analysis (EDA). The formation of hollow cages rather than centre-filled icosahedrons in the Au₁₄₄ clusters is attributed to the significant Pauli repulsion between the central gold atom and the surrounding metal shell, which leads to the decrease of the averaged formation energy of the clusters. The present study also shows that the Au₁₄₄ cluster is unique in size. The smaller size clusters Au₁₃₃ and Au₁₃₀ and the larger size cluster Au₂₇₉ both preferred the centre-filled golden icosahedrons, decahedrons or octahedrons.

Correlating structural rules with electronic properties of ligand-protected alloy nanoclusters

Thiolate protected gold nanoclusters (TPNCs) are a unique class of nanomaterials finding applications in various fields, such as biomedicine, optics, and catalysis. The atomic precision of their structure, characterized through single crystal x-ray diffraction, enables the accurate investigation of their physicochemical properties through electronic structure calculations. Recent experimental efforts have led to the successful heterometal doping of TPNCs, potentially unlocking a large domain of bimetallic TPNCs for targeted applications. However, how TPNC size, bimetallic composition, and location of dopants influence electronic structure is unknown. To this end, we introduce novel structure-property relationships (SPRs) that predict electronic properties such as ionization potential (IP) and electron affinity (EA) of AgAu TPNCs based on physically relevant descriptors. The models are constructed by first generating a hypothetical AgAu TPNC dataset of 368 structures with sizes varying from 36 to 279 metal atoms. Using our dataset calculated with density functional theory (DFT), we employed systematic analyses to unravel size, composition, and, importantly, core-shell effects on TPNC EA and IP behavior. We develop generalized SPRs that are able to predict electronic properties across the AgAu TPNC materials space. The models leverage the same three fundamental descriptors (i.e., size, composition, and core-shell makeup) that do not require DFT calculations and rely only on simple atom counting, opening avenues for high throughput bimetallic TPNC screening for targeted applications. This work is a first step toward finely controlling TPNC electronic properties through heterometal doping using high throughput computational means.

High photoluminescence from self-assembled Ag2Cl2(dppe)2 clusters through metallophilic interactions

Ligand protected metal nanoclusters (NCs) are an emerging class of functional materials with intriguing photophysical and chemical properties. The size and molecular structure play an important role in endowing NCs with characteristic optical and electronic properties. Modulation of these properties through the chemical reactivity of NCs is largely unexplored. Here, we report on the synthesis of self-assembled Ag₂Cl₂(dppe)₂ clusters through the ligand-exchange-induced transformation of [Pt₂Ag₂₃Cl₇(PPh₃)₁₀] NCs [(dppe): 1,2-bis(diphenylphosphino)ethane; (PPh₃): triphenylphosphine]. The single crystal x-ray structure reveals that two Ag atoms are bridged by one dppe and two Cl ligands, forming a Ag₂Cl₂(dppe) cluster, which is subsequently self-assembled through dppe ligands to form [Ag₂Cl₂(dppe)₂]_n. Importantly, the Ag₂Cl₂(dppe)₂ cluster assembly exhibits high photoluminescence quantum yield: ∼18%, which is attributed to the metallophilic interactions and rigidification of the ligand shell. We hope that this work will motivate the exploitation of the chemical reactivity of NCs as a new path to attain cluster assemblies endowed with enhanced photophysical properties.

Atom-by-Atom Evolution of the Same Ligand-Protected Au21, Au22, Au22Cd1, and Au24 Nanocluster Series

Atom-by-atom manipulation on metal nanoclusters (NCs) has long been desired, as the resulting series of NCs can provide insightful understanding of how a single atom affects the structure and properties as well as the evolution with size. Here, we report crystallizations of Au22(SAdm)16 and Au22Cd1(SAdm)16 (SAdm = adamantanethiolate) which link up with Au21(SAdm)15 and Au24(SAdm)16 NCs and form an atom-by-atom evolving series protected by the same ligand. Structurally, Au22(SAdm)16 has an Au3(SAdm)4 surface motif which is longer than the Au2(SAdm)3 on Au21(SAdm)15, whereas Au22Cd1(SAdm)16 lacks one staple Au atom compared to Au24(SAdm)16 and thus the surface structure is reconstructed. A single Cd atom triggers the structural transition from Au22 with a 10-atom bioctahedral kernel to Au22Cd1 with a 13-atom cuboctahedral kernel, and correspondingly, the optical properties are dramatically changed. The photoexcited carrier lifetime demonstrates that the optical properties and excited state relaxation are highly sensitive at the single atom level. By contrast, little change in both ionization potential and electron affinity is found in this series of NCs by theoretical calculations, indicating the electronic properties are independent of adding a single atom in this series. The work provides a paradigm that the NCs with continuous metal atom numbers are accessible and crystallizable when meticulously designed, and the optical properties are more affected at the single atom level than the electronic properties.

Heteroatom Tracing Reveals the 30-Atom Au-Ag Bimetallic Nanocluster as a Dimeric Structure

Understanding the formation of face-centered cubic (fcc) nanostructures at the atomic level remains a major task. With atomically precise nanoclusters (NCs) as model systems, herein we devised an atom-tracing strategy by heteroatom doping into Au₃₀(SR)₁₈ (SR = S-^tC₄H₉) to label the specific positions in M₃₀(SR)₁₈ NCs (M = Au/Ag), which clearly reveals the dimeric nature of M₃₀. Interestingly, the specific position is also consistent with the Ag-doping site in M₂₁(SR)₁₅. Electronic orbital analysis shows intrinsic orbital localization at the two specific positions in M₃₀, which are decisive to the electronic structure of M₃₀, regardless of Au or Ag occupancy. The fcc dimeric NC, which would not be discovered without Ag tracing, provides a possible explanation for the wide accessibility of nonsuperatomic Au-SR NCs.

Rapid Prediction of Bimetallic Mixing Behavior at the Nanoscale

The nanoparticle (NP) design space allows for variations in size, shape, composition, and chemical ordering. In the search for low-energy structures, this results in an extremely large search space which cannot be screened by brute force methods. In this work, we develop a genetic algorithm to predict stable bimetallic NPs of any size, shape, and metal composition. Our method predicts nanostructures in agreement with experimental trends and it captures the detailed chemical ordering of an experimental 23,196-atom FePt NP with nearly atom-by-atom accuracy. Our developed screening process is extremely fast, allowing us to generate and analyze a database of 5454 low-energy bimetallic NPs. By identifying thermodynamically stable NPs, we rationalize bimetallic mixing at the nanoscale and reveal metal-, size-, and temperature-dependent mixing behavior. Importantly, our method is applicable to any bimetallic NP size, bridging the materials gap in nanoscale simulations, and guides experimentation in the lab by elucidating stability, mixing, and detailed chemical ordering behavior of bimetallic NPs.

Towards elucidating structure of ligand-protected nanoclusters

Developing a centralized database for ligand-protected nanoclusters can fuel machine learning and data-science-based approaches towards theoretical structure prediction.