Pyrazole‐Protected Heteronuclear Rare‐Earth Boron‐Oxo Cluster Cage With Tunable Luminescence

ABSTRACT Rare‐earth boron‐oxo clusters, which combine the structural diversity of borates with the unique chemical properties of rare‐earth ions, represent a promising platform for advanced functional materials. Herein, we report the synthesis and characterization of a series of heteronuclear rare‐earth boron‐oxo clusters ( BOCs ), [RE ₃ B ₉ (μ ₃ ‐O) ₁₂ Pz ₆ HPz ₆ Cl ₆ ] ( BOC‐9 , Pz = pyrazolate, HPz = pyrazole), [RE ₃ B ₉ (μ ₃ ‐O) ₁₂ Pz ₇ HPz ₆ (MeO) ₂ Cl ₃ ] ( BOC‐10 ), and [RE(NO ₃ ) ₆ RE ₅ B ₁₈ (μ ₃ ‐O) ₂₄ Pz ₁₈ ] _n ( BOC‐11 ), where RE = Dy ^{3 +} /Y ^{3 +} . Structural evolution from discrete to 2‐dimensional (2D) architectures was achieved through systematic variation of boron sources and rare‐earth salts. These clusters exhibit a well‐defined stability gradient correlated with increasing organic ligands and structural dimensionality. Spectroscopic characterizations uncover two distinct photoluminescence emission mechanisms in the boron‐oxo based functional materials. Dy ^{3 +} ‐based BOCs exhibit typical f‐f transition emissions, which are effectively sensitized by the ligand‐to‐metal charge transfer (LMCT) process, whereas closed‐shell Y ^{3 +} ‐based BOCs show exclusive photoluminescence derived from the ligand‐to‐boron charge transfer pathway. Dynamic B─N bond cleavage, as evidenced by electrospray ionization mass spectrometry (ESI‐MS), enables isolation of cluster cores, providing mechanistic insights into structural rearrangements. This work establishes design principles for next‐generation luminescent materials based on rare‐earth boron‐oxo clusters.