An Ultrastable Matryoshka [Hf13] Nanocluster as a Luminescent Sensor for Concentrated Alkali and Acid

Stable metal clusters that can resist both highly concentrated acid and alkali are unknown. Herein, we present a discrete neutral cluster, Hf13(μ4‐O)8(OCH3)36 (1), which features extraordinary chemical stability by preserving its crystalline state in concentrated aqueous solutions of both acid (10 m HNO3) and alkali (20 m boiling NaOH). Importantly, 1 can serve as a luminescent probe for detecting both concentrated alkali (20 m NaOH) and strong acid (1 m HNO3) with high selectivity and repeatability. DFT studies of the electronic structure and bonding revealed that 1 has an extremely large HOMO–LUMO gap due to strong d π–p π bonding that accounts for the ultrahigh stability. Tough beyond belief: An ultrastable Hf13(μ4‐O)8(OCH3)36 nanocluster (see picture; Hf green, O red, C gray) preserved its crystalline state in concentrated alkali (20 m boiling NaOH) and concentrated acid (10 m HNO3). The cluster acted as a luminescent sensor for the detection of both strong acid and concentrated alkali with high selectivity and repeatability.