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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.

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.