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Coinage-metal clusters with excellent luminescence properties have attracted considerable interest due to their intriguing structures and potential applications. However, achieving strong near-infrared (NIR) luminescence in these clusters is highly challenging. Here, we have successfully synthesized the first LnIII/CuIbimetallic clusters, formulated as [LnCu54O6Cl3(2-MeO-PhC≡C)36] (ClO4)6(Ln = Yb for YbCu54, Er for ErCu54, and Gd for GdCu54). Single crystal X-ray diffraction showed that the LnCu54clusters have a three-layered core–shell structure, consisting of (LnO6)@Cu18Cl3@Cu36units protected by 36 2-MeO-PhC≡C–ligands. Notably, the YbCu54cluster exhibits significant NIR-II luminescence at 986 nm with the solid quantum efficiency of 33.3%, the highest among Cu clusters with NIR-II emission. This work not only reports the first category of LnIII/CuIclusters but also presents a method to enhance NIR luminescence in coinage-metal clusters through the incorporation of LnIIIions.

The magneto-optical response of chiral materials holds significant potential for applications in physics, chemistry, and biology. However, exploration of the near-infrared (NIR) magneto-optical response remains limited. Herein, we report the synthesis and strong NIR-II magneto-optical activity of three pairs of chiral 3d–4fclusters of R/S-Ln15Cu54(Ln = Sm, Gd, and Dy). Structural analysis reveals that R/S-Ln15Cu54features a triangular prism cage with C3symmetry. Interestingly, magnetic circular dichroism (MCD) spectra exhibit remarkable magneto-optical response in the NIR-II region, driven by the f–ftransition. The maximum g-factor of R/S-Sm15Cu54reaches 5.5 × 10–3T–1around 1300–1450 nm, surpassing values associated with DyIIIand CuIIions. This remarkable NIR-II magneto-optical activity may be attributed to strong magnetic-dipole-allowed f–ftransitions and helix chirality of the structure. This work not only presents the largest Ln-Cu clusters to date but also demonstrate the key role of magnetic-dipole-allowed transitions on magneto-optical activity.