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Several recent studies have demonstrated the great promise of ligand-protected atomically precise copper nanoclusters in driving various chemical transformation processes. The insights into key factors in controlling the catalytic performance of copper clusters at the molecular level are highly desirable but difficult to gain. Herein, we report the synthesis and comprehensive characterization of two novel Cu20nanoclusters, with the molecular formulae of Se@Cu20(PhSe)12(PPh3)2(C6H5COO)6(Cu20-1) and Se@Cu20(PhSe)12(PPh3)2(CF3COO)6(Cu20-2), which are proved to be great candidates in clarifying the structure and property relationship in catalysis. As revealed by single-crystal X-ray analysis, the two Cu20structures share an identical metal skeleton and similar ligand distributions with the only difference being in the carboxylate ligands on the surface: C6H5COO for Cu20-1 while CF3COO for Cu20-2. Surprisingly, such small distinctions in the structure cause a 16-fold catalytic activity leap in the catalytic reduction of 4-nitrophenol to 4-aminophenol. The electronic structures of the resulting clusters are distinct, which accounts for their distinct catalytic performances. This work not only provides a model system to highlight the importance of the carboxylate structures on controlling the catalysis of copper clusters but, more importantly, is also expected to simulate research attention on carboxylate engineering to modulate physicochemical properties of carboxylate-functionalized copper metal nanoclusters beyond catalysis.

Owing to the inherent instability caused by the low Cu(I)/Cu(0) half-cell reduction potential, Cu(0)-containing copper nanoclusters are quite uncommon in comparison to their Ag and Au congeners. Here, a novel eight-electron superatomic copper nanocluster [Cu31(4-MeO-PhC≡C)21(dppe)3](ClO4)2(Cu31, dppe = 1,2-bis(diphenylphosphino)ethane) is presented with total structural characterization. The structural determination reveals that Cu31features an inherent chiral metal core arising from the helical arrangement of two sets of three Cu2units encircling the icosahedral Cu13core, which is further shielded by 4-MeO-PhC≡C–and dppe ligands. Cu31is the first copper nanocluster carrying eight free electrons, which is further corroborated by electrospray ionization mass spectrometry, X-ray photoelectron spectroscopy and density functional theory calculations. Interestingly, Cu31demonstrates the first near-infrared (750–950 nm, NIR-I) window absorption and the second near-infrared (1000–1700 nm, NIR-II) window emission, which is exceptional in the copper nanocluster family and endows it with great potential in biological applications. Of note, the 4-methoxy groups providing close contacts with neighboring clusters are crucial for the cluster formation and crystallization, while 2-methoxyphenylacetylene leads only to copper hydride clusters, Cu6Hor Cu32H14. This research not only showcases a new member of copper superatoms but also exemplifies that copper nanoclusters, which are nonluminous in the visible range may emit luminescence in the deep NIR region.

Growing attention has been paid to nanoclusters with face-centered cubic (fcc) metal kernels, due to its structural similarity to bulk metals. We demonstrate that the use of tetradentate formamidinate ligands facilitate the construction of two fcc silver nanoclusters: [Ag52(5-F-dpf)16Cl4](SbF6)2(Ag52, 5-F-Hdpf = N,N′-di(5-fluoro-2-pyridinyl)formamidine) and [Ag53(5-Me-dpf)18](NO3)5(Ag53, 5-Me-Hdpf = N,N′-di(5-methyl-2-pyridinyl)formamidine). Single-crystal X-ray structural analysis revealed that the silver atoms in both clusters are in a layer-by-layer arrangement, which can be viewed as a portion of the fcc packing of silver. The nitrogen donors of amidinate ligands selectively passivate the {111} facets. All silver atoms are involved in the fcc packing, that is, no staple motifs are observed due to the linear arrangement of the four N donors of the dpf ligands. The characteristic optical absorption bands of Ag52and Ag53have been studied with a time-dependent density functional theory. This work provides a facile access to assembling atomically precise fcc-type nanoclusters and shows the prospect of amidinates as protecting ligands in synthesizing metal nanoclusters.

A pair of alkynyl–diphosphine-coprotected copper(I) clusters, namely, [Cu6(4-MeO-PhC≡C)5(dppe)3](ClO4) [Cu6; dppe = 1,2-bis(diphenylphosphino)ethane] and [Cu11(H)(4-MeO-PhC≡C)8(dpppe)3](ClO4)2[Cu11; dpppe = 1,5-bis(diphenylphosphino)pentane], featuring trigonal-prismatic frameworks have been synthesized by a reduction method. Their molecular structures are determined by X-ray crystallography and characterized by multiple techniques. The length of the spacer of the diphosphine ligand can directly affect the aspect ratio of the clusters. Cu6with dppe as ligands has a trigonal-prismatic core. The longer alkyl spacer of dpppe helps to elongate the trigonal-prismatic framework to form Cu11, with its trigonal-prismatic framework encapsulating a Cu5H unit. Electrospray ionization mass spectrometry, 2H NMR, and liberations of hydrogen further verify the presence of a hydride in the cluster. Density functional theory calculations help to locate the position of the hydride and understand the electronic structures of the clusters. Cu11is the first alkynyl–phosphine-coprotected copper hydride cluster. These two clusters show distinct luminescence properties. The compact Cu6is phosphorescent upon radiation, while the longer Cu11with more flexibility is nonluminous. This work enriches the family of copper hydrides and demonstrates the ligand effects in the extension of the length and structural complexity of clusters.

Identification of the authentic active species of cluster catalysis is rather challenging, and direct structural evidence is quite valuable and difficult to obtain. Two “isostructural” clusters, Ag25Cu4Cl6(dppb)6(PhC≡C)12(SO3CF3)3(1) and Ag25Cu4Cl6H8(dppb)6(PhC≡C)12(SO3CF3)3(2H) (dppb is 1,4-bis(diphenylphosphine)butane), have been successfully isolated and structurally characterized. Both these clusters have a centered icosahedron Ag13core with the same peripheral composition and structure. The only difference is that 2Hhas eight hydrides but 1has none, that is, the kernels are Ag135+and Ag13H85+in 1and 2H, respectively. The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as a model reaction is assessed with the two clusters. Cluster 2His very active with 100% yield within 2 h, whereas 1shows a very low conversion (∼8%) under the same conditions. Interestingly, high catalytic activity was observed when 1was converted to 2Hwith the oxidation of H2O2under catalytic conditions. The unprecedented transformation of a reduced nanocluster to an Ag(I)Cu(I) bimetallic cluster compound provides an excellent platform to determine the real active cluster in terms of metal cluster catalysis. The present work presents clear structural evidence that the catalytic performance of metal nanoclusters can be modulated by properly regulating the oxidation state of their constituted metal atoms.

An atomically resolved gold nanocluster Au99(C≡CC6H3-2,4-F2)40(Au99) with an unusual 59 valence electrons has been synthesized. Single-crystal X-ray diffraction reveals that its Au79kernel is a Au49Marks decahedron capped by two Au15units. The surface structure of Au99consists of 20 linear Au(C≡CR)2staples. Intercluster interactions are observed between these D5symmetric clusters. The existence of an unpaired electron is verified by magnetic measurement. Interestingly, this open-shell gold cluster Au99stays intact in toluene solution at 80 °C for more than a week, and it has good charging–discharging capability under electrochemical conditions. The compact ligand shell protection around the symmetric core accounts for the high stability. This work suggests that geometric factors may play a crucial role in determining the stability of a metal nanocluster, even though the cluster has an open-shell electronic structure.

The boundary between molecular and metallic gold nanoclusters is of special interest. The difficulty in obtaining atomically precise nanoclusters larger than 2 nm limits the determination of such a boundary. The synthesis and total structural determination of the largest all-alkynyl-protected gold nanocluster (Ph4P)6[Au156(C≡CR)60] (R = 4-CF3C6H4-) (Au156) are reported. It presents an ideal platform for studying the relationship between the structure and the metallic nature. Au156has a rod shape with the length and width of the kernel being 2.38 and 2.04 nm, respectively. The cluster contains a concentric Au126core structure (Au46@Au50@Au30) protected by 30 linear RC≡C–Au–C≡CR staple motifs. It is interesting that Au156displays multiple excitonic peaks in the steady-state absorption spectrum (molecular) and pump-power-dependent excited-state dynamics as revealed in the transient absorption spectrum (metallic), which indicates that Au156is a critical crossover cluster for the transition from molecular to metallic state. Au156is the smallest-sized gold nanocluster showing metal-like electron dynamics, and it is recognized that the cluster shape is one of the important factors determining the molecular or metallic nature of a gold nanocluster.

Tailoring the surface ligands of metal nanoclusters is important for engineering unique configurations of metal nanoclusters. Thiacalix[4]arene has found extensive applications in the construction of metal nanoclusters. In this investigation, we present the synthesis and characterization of the first all-calixarene-protected silver nanoclusters, [Ag(CH3CN)4]2[Ag44(BTCA)6] (Ag44, H4BTCA = p-tert-butylthiacalix[4]arene). Single-crystal X-ray structural analysis reveals that all silver atoms are in a face-centered cubic (fcc) arrangement. The formation of such an fccstructure is attributed to the selectively passivation on {100} facets by BTCA4–. Thiacalixarene substantially facilitates the stability of Ag44due to its multiple coordination sites and bulkiness. Mass spectrometry and theoretical calculations reveal that Ag44is a superatomic silver nanocluster with 22 free electrons in the following configuration: 1S21P61D61F22S21D4. This work not only elucidates the impact of macrocyclic ligands on the stabilization of silver clusters but also furnishes an approach for assembling atomically precise fccnanoclusters.

It remains a grand challenge to amplify the chiroptical activity of chiral metal nanoclusters (NCs) although it is desirable for fundamental research and practical application. Herein, we report a strategy of surface/interface solidification (SIS) for enhancing the chiroptical activity of gold NCs. Structural analysis of [Au19(2R,4R/2S,4S-BDPP)6Cl2]3+(BDPP is 2,4-bis(diphenylphosphino)pentane) clusters reveals that one of the interfacial gold atoms is flexible between two sites and large space is present on the surface, thus hampering chirality transfer from surface chiral ligands to metal core and leading to low chiroptical activity. Following SIS by filling the flexible sites and replacing chlorides with thiolate ligands affords another pair of [Au20(2R,4R/2S,4S-BDPP)6(4-F-C6H4S)2]4+, which shows a more compact and organized structure and thus an almost 40-fold enhancement of chiroptical activity. This work not only provides an efficient approach for amplifying the chiroptical activity of metal nanoclusters but also highlights the significance of achiral components in shaping chiral nanostructures.

We report the controlled synthesis and structures of two isomeric gold nanoclusters, whose compositions are determined to be Au23(C≡CBut)15(denoted as Au23-1and Au23-2) by single-crystal X-ray diffraction and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. This is the first time isomerism is discovered in alkynyl-protected gold nanoclusters. The metal-to-ligand ratios in these two clusters are different from known Aun(SR)msystems and have not been observed in the Aux(C≡CPh)yfamily. This pair of isomers exhibits different optical properties, although they have similar structures and identical components. For both Au23clusters, time-dependent density functional theory calculations revealed the frontier orbitals highest occupied molecular orbital (HOMO)–1, HOMO, and lowest unoccupied molecular orbital (LUMO) are mainly constructed from the Au15kernel and V-shaped alkynyl–gold motifs. The HOMO → LUMO transition of Au23-1is optically forbidden, whereas it is allowed in Au23-2. It is also found that Au23-2cluster can be transformed to Au23-1spontaneously under ambient conditions. This work offers further insight into the synthesis and isomerism of all-alkynyl-protected gold nanoclusters and will stimulate more investigation of isomeric metal nanoclusters.

A pair of enantiopure Au13nanoclusters have been enantioselectively synthesized by chiral ligands with stereogenic centers at the phosphorus atoms. Their structures are determined by X-ray crystallography, which are typical models with a high symmetric core and chiral surface ligand arrangement. Correlation between the crystallographic structure, the calculation, and the circular dichroism (CD) study indicates that helical ligand arrangement inducing the core into chiral distortion accounts for the chiroptical activities in the visible region. A rare example of cocrystallization of a mixture of diastereomers has been observed for the first time for gold nanoclusters, reflecting the lack of chiral self-sorting of the ligands.

We report the synthesis and crystal structure determination of two novel chiral gold nanoclusters. By utilizing BINAP, we isolate atomically precise intrinsically chiral Au nanoclusters [Au9(R-/S-BINAP)4](CF3COO)3and [Au10(R-/S-BINAP)4(p-CF3C6H4C≡C)](CF3COO)3in high yield with one-pot synthesis. Au9has C2geometry, while Au10is C1symmetric. Interestingly, reversible interconversion between Au9and Au10can be realized by the addition or removal of a RC≡CAu component. The transformation from Au9to Au10leads to significant enhancement of CD signals. The maximum anisotropy factor in the visible region of [Au10(BINAP)4(p-CF3C6H4C≡C)]3+is the hitherto largest (up to 6.6 × 10–3) among gold nanoclusters, which is approximately twice of that of [Au9(BINAP)4]3+. This work demonstrates that the chiroptical activity of gold nanoclusters can be modulated by structural control through the introduction of second ligands.

The past decades have witnessed great advances in the synthesis, structure determination, and properties investigation of coinage metal nanoclusters. These monodisperse clusters have well-defined molecular structures, which is advantageous in correlating structures and properties. Metal nanoclusters are large molecules consisting of many components, so it is a big challenge to prepare them in a rational way. Strenuous efforts have been made to control their geometric and electronic structures, in order to optimize their various properties.

Porous materials have been widely applied for supercapacitors; however, the relationship between the electrochemical behaviors and the spatial structures has rarely been discussed before. Herein, we report a series of porous coordination cage (PCC) flexible supercapacitors with tunable three-dimensional (3D) cavities and redox centers. PCCs exhibit excellent capacitor performances with a superior molecular capacitance of 2510 F mmol–1, high areal capacitances of 250 mF cm–2, and unique cycle stability. The electrochemical behavior of PCCs is dictated by the size, type, and open–close state of the cavities. Both the charge binding site and the charge transportation pathway are unambiguously elucidated for PCC supercapacitors. These findings provide central theoretical support for the “structure–property relationship” for designing powerful electrode materials for flexible energy storage devices.

The first mixed-valence nanocluster CuI/CuIIwith the highest percentage of CuIIions was synthesized by using 4-tert-butylcalix[4]arene (Calix4), with the formula DMF2⊂[(CO3)2-@CuII6CuI3(Calix4)3Cl2(DMF)5(H3O)]•DMF (1), as a photothermal nanocluster. Its structure was characterized using single-crystal X-ray diffraction, Fourier-transform infrared spectroscopy, and powder X-ray diffraction. In addition, the charge state and chemical composition of the nanocluster were determined using electrospray ionization spectrometry and X-ray photoelectron spectroscopy (XPS) spectrum. The results of the XPS and X-ray crystallography revealed that there are two independent CuIIand CuIcenters in nanocluster 1with the relative abundances of 66.6 and 33.3% for CuIIand CuI, respectively. The nanocluster contains three four-coordinated CuIions with a square-planar geometry and six five-coordinated CuIIions with a square pyramid geometry. The nanocluster shows strong near-infrared optical absorption in the solid state and excellent photothermal conversion ability (the equilibrium temperature ∼78.2 °C) with the light absorption centers in 286–917 nm over previous reported pentanucleus CuI4CuIIclusters and CuIIcompounds.

A 64-nuclearity silver cluster encapsulating a unique POM anion [MnIIIMnIV2Mo14O56]17–has been synthesized. The formation of the templating core performs a reassembly process for increasing nuclearities from {MnMo9} to {Mn3Mo14}. It represents a rare inorganic meso anion containing mixed-valent Mn that is built up by d-{MnIVMo7} and l-{MnIVMo7} units connecting together through a {MnIII} fragment.