An Ultrastable Matryoshka [Hf 13 ] 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, Hf 13 (μ 4 ‐O) 8 (OCH 3 ) 36 ( 1 ), which features extraordinary chemical stability by preserving its crystalline state in concentrated aqueous solutions of both acid (10  m HNO 3 ) 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 HNO 3 ) 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.