Chirality is ubiquitous in nature and occurs at all length scales. The development of applications for chiral nanostructures is rising rapidly. With the recent achievements of atomically precise ...nanochemistry, total structures of ligand‐protected Au and other metal nanoclusters (NCs) are successfully obtained, and the origins of chirality are discovered to be associated with different parts of the cluster, including the surface ligands (e.g., swirl patterns), the organic–inorganic interface (e.g., helical stripes), and the kernel. Herein, a unified picture of metal–ligand surface bonding‐induced chirality for the nanoclusters is proposed. The different bonding modes of M–X (where M = metal and X = the binding atom of ligand) lead to different surface structures on nanoclusters, which in turn give rise to various characteristic features of chirality. A comparison of Au–thiolate NCs with Au–phosphine ones further reveals the important roles of surface bonding. Compared to the Au–thiolate NCs, the Ag/Cu/Cd–thiolate systems exhibit different coordination modes between the metal and the thiolate. Other than thiolate and phosphine ligands, alkynyls are also briefly discussed. Several methods of obtaining chiroptically active nanoclusters are introduced, such as enantioseparation by high‐performance liquid chromatography and enantioselective synthesis. Future perspectives on chiral NCs are also proposed.
Atomically precise, ligand‐protected metal nanoclusters provide an excellent opportunity to reveal that chirality is intrinsic and “outside‐in.” A unified picture of metal–ligand surface bonding‐induced chirality is provided; that is, the Aun(SR)n+1 staple motifs, Agn(SR)m mount motifs, and even the whole Ag‐SR cage are responsible for the chirality in Au‐SR and Ag‐SR nanoclusters.
Conspectus Ultrasmall metal nanoparticles (often called nanoclusters) possess unique geometrical structures and novel functionalities that are not accessible in conventional nanoparticles. Recent ...progress in their synthesis and structural determination by X-ray crystallography has led to deep understanding of the structural evolution, structure–property correlation, and growth modes, such as the layer-by-layer growth in face-centered cubic (fcc)-type nanoclusters, linear assembly of vertex-shared icosahedral units, and other unique modes. The enriched knowledge on the correlation between the structure and the properties has rendered metal nanoclusters a new class of functional nanomaterials. Despite the significant achievements in structural determinations, mapping out the structure–property correlation is still very challenging because of the core–shell structures of nanoclusters (e.g., Au n (SR) m protected by thiolate ligands) with metal atoms partitioned between the core and the shell. In such structures, the core and the surface are entangled and cannot be separately studied because changing the core structure would inevitably change the surface (or vice versa). Thus, it is of great importance to develop the “tailoring” chemistry for structural modification of the core (or surface) while retaining the other parts, in order to achieve fundamental understanding of what part of the nanocluster structure plays what role in the functionalities. In this Account, we summarize some recent work on the strategies to control the atomic structures of metal nanoclusters for tuning their properties, such as stability, optical absorption, excited-state electron dynamics, and photoluminescence, as well as their catalytic reactivity. The development of a ligand-based strategy has permitted the synthesis of structural isomers of nanoclusters with the same size but different functionalities. Successful modification of the core (or surface) structure while maintaining the other components has led us to gain some fundamental understanding of the respective roles of the core and the surface in the nanocluster functionalities. Such “tailoring” chemistry on metal nanoclusters can provide a strong basis for functional nanomaterials consisting of nanocluster components with desired properties. Further development of the tailoring chemistry will guide materials chemists to new directions and tailor-made functional nanomaterials for specific applications.
We report a three-orders-of-magnitude variation of carrier lifetimes in exotic crystalline phases of gold nanoclusters (NCs) in addition to the well-known face-centered cubic structure, including ...hexagonal close-packed (hcp) Au
and body-centered cubic (bcc) Au
NCs protected by the same type of capping ligand. The bcc Au
NC had an exceptionally long carrier lifetime (4.7 microseconds) comparable to that of bulk silicon, whereas the hcp Au
NC had a very short lifetime (1 nanosecond). Although the presence of ligands may, in general, affect carrier lifetimes, experimental and theoretical results showed that the drastically different recombination lifetimes originate in the different overlaps of wave functions between the tetrahedral Au
building blocks in the hierarchical structures of these NCs.
The evolution of the optical properties of gold nanoclusters (NCs) versus size is of great importance because it not only reveals the nature of quantum confinement in NCs, but also helps to ...understand how the molecular-like Au NCs transit to plasmonic nanoparticles. While some work has been done in studying the optical properties of NCs of certain individual sizes, the global picture remains unclear, such as the detailed relationship between size/structure and properties. Here, we investigate the grand evolution of the optical properties by comparing the steady-state absorption, bandgap, transient absorption, as well as carrier dynamics of a series of thiolate-protected gold NCs ranging from tens to hundreds of gold atoms. We find that, on the basis of their optical behaviors, gold NCs can be classified into three groups: (i) ultrasmall NCs (ca. <50 Au atoms) are nonscalable as their optical properties are strongly dependent on the structure rather than size; (ii) medium-sized NCs (about 50–100 Au atoms) show both size- and structure-dependent optical properties; and (iii) large-sized gold NCs (ca. >100 Au atoms) exhibit optical properties solely dependent on size, and the structure effect fades out. Unraveling the grand evolution from nonscalable to scalable optical properties and their mechanisms will greatly deepen scientific understanding of the nature of quantum-sized gold NCs and will also provide implications for plasmonic NPs.
Recent advances in the synthetic chemistry of atomically precise metal nanoclusters (NCs) have significantly broadened the accessible sizes and structures. Such particles are well defined and have ...intriguing properties, thus, they are attractive for catalysis. Especially, those NCs with identical size but different core (or surface) structure provide unique opportunities that allow the specific role of the core and the surface to be mapped out without complication by the size effect. Herein, we summarize recent work with isomeric Aun NCs protected by ligands and isostructural NCs but with different surface ligands. The highlighted work includes catalysis by spherical and rod‐shaped Au25 (with different ligands), quasi‐isomeric Au28(SR)20 with different R groups, structural isomers of Au38(SR)24 (with identical R) and Au38S2(SR)20 with body‐centred cubic (bcc) structure, and isostructural Au38L20(PPh3)42+ (different L). These isomeric and/or isostructural NCs have provided valuable insights into the respective roles of the kernel, surface staples, and the type of ligands on catalysis. Future studies will lead to fundamental advances and development of tailor‐made catalysts.
Every atom counts: Recent advances in metal nanocluster chemistry have realized isomers and/or isostructural nanoclusters. Catalytic applications of such nanoclusters allow a deeper insight to be obtained into the respective roles of the respective structural parts on catalytic performance without complication by the size effect.
Nanoscience has progressed tremendously in the exploration of new phenomena not seen in bulk materials, however, the transition between nanoscale and bulk properties is not yet fully understood. Here ...the authors identify and discuss remaining open questions that call for future efforts.
The origin of the near-infrared photoluminescence (PL) from thiolate-protected gold nanoclusters (Au NCs, <2 nm) has long been controversial, and the exact mechanism for the enhancement of quantum ...yield (QY) in many works remains elusive. Meanwhile, based upon the sole steady-state PL analysis, it is still a major challenge for researchers to map out a definitive relationship between the atomic structure and the PL property and understand how the Au(0) kernel and Au(I)–S surface contribute to the PL of Au NCs. Herein, we provide a paradigm study to address the above critical issues. By using a correlated series of “mono-cuboctahedral kernel” Au NCs and combined analyses of steady-state, temperature-dependence, femtosecond transient absorption, and Stark spectroscopy measurements, we have explicitly mapped out a kernel-origin mechanism and clearly elucidate the surface–structure effect, which establishes a definitive atomic-level structure–emission relationship. A ∼100-fold enhancement of QY is realized via suppression of two effects: (i) the ultrafast kernel relaxation and (ii) the surface vibrations. The new insights into the PL origin, QY enhancement, wavelength tunability, and structure–property relationship constitute a major step toward the fundamental understanding and structural-tailoring-based modulation and enhancement of PL from Au NCs.
We report the synthesis and crystal structure determination of a gold nanocluster with 103 gold atoms protected by 2 sulfidos and 41 thiolates (i.e., 2-naphthalenethiolates, S-Nap), denoted as ...Au103S2(S-Nap)41. The crystallographic analysis reveals that the thiolate ligands on the nanocluster form local tetramers by intracluster interactions of C–H···π and π···π stacking. The herringbone pattern formation via intercluster interactions is also observed, which leads to a linearly connected zigzag pattern in the single crystal. The kernel of the nanocluster is a Marks decahedron of Au79, which is the same as the kernel of the previously reported Au102(pMBA)44 (pMBA = −SPh-p-COOH); this is a surprise given the much bulkier naphthalene-based ligand than pMBA, indicating the robustness of the decahedral structure as well as the 58-electron configuration. Despite the same kernel, the surface structure of Au103 is quite different from that of Au102, indicating the major role of ligands in constructing the surface structure. Other implications from Au103 and Au102 include (i) both nanoclusters show similar HOMO–LUMO gap energy (i.e., E g ≈ 0.45 eV), indicating the kernel is decisive for E g while the surface is less critical; and (ii) significant differences are observed in the excited-state lifetimes by transient absorption spectroscopy analysis, revealing the kernel-to-surface relaxation pathway of electron dynamics. Overall, this work demonstrates the ligand-effected modification of the gold–thiolate interface independent of the kernel structure, which in turn allows one to map out the respective roles of kernel and surface in determining the electronic and optical properties of the 58e nanoclusters.
Atomically precise nanoclusters of coinage metals in the 1-3 nm size regime have been intensively pursued in recent years. Such nanoclusters are attractive as they fill the gap between small ...molecules (<1 nm) and regular nanoparticles (>3 nm). This intermediate identity endows nanoclusters with unique physicochemical properties and provides nanochemists opportunities to understand the fundamental science of nanomaterials. Metal nanoparticles are well known to exhibit plasmon resonances upon interaction with light; however, when the particle size is downscaled to the nanocluster regime, the plasmons fade out and step-like absorption spectra characteristic of cluster sizes are manifested due to strong quantum confinement effects. Recent research has revealed that nanoclusters are commonly composed of a distinctive kernel and a surface-protecting shell (or staple-like metal-ligand motifs). Understanding the kernel configuration and evolution is one of the central topics in nanoscience research. This Review summarizes the recent progress in identifying the growth patterns of atomically precise coinage nanoclusters. Several basic kernel units have been observed, such as the M
4
, M
13
and M
14
polyhedrons (where, M = metal atom). Among them, the tetrahedral M
4
and icosahedral M
13
units are the most common ones, which are adopted as building blocks to construct larger kernel structures
via
various fusion or aggregation modes, including the vertex- and face-sharing mode, the double-strand and alternate single-strand growth, and cyclic fusion of units, as well as the fcc-based cubic growth pattern. The identification of the kernel growth pathways has led to deeper understanding of the evolution of electronic structure and optic properties.
This mini-Review summarizes the fusion growth patterns of metal nanoclusters based upon M
4
, M
13
and M
14
building blocks.
Understanding the isomerism phenomenon at the nanoscale is a challenging task because of the prerequisites of precise composition and structural information on nanoparticles. Herein, we report the ...ligand-induced, thermally reversible isomerization between two thiolate-protected 28-gold-atom nanoclusters, i.e. Au28(S-c-C6H11)20 (where -c-C6H11 = cyclohexyl) and Au28(SPh-tBu)20 (where -Ph-tBu = 4-tert-butylphenyl). The intriguing ligand effect in dictating the stability of the two Au28(SR)20 structures is further investigated via dispersion-corrected density functional theory calculations.