Anion Electronegativity Regulates d-Orbital Activation under High Pressure

Pressure-induced activation of previously inactive electronic states can drive unconventional chemical phenomena, yet the chemical factors governing orbital activation remain unclear. Here, using Sr-Ch (Ch═O, S, Se, and Te) compounds as a model system, we uncover an anion-electronegativity-regulated mechanism for pressure-induced Sr 4d activation through first-principles calculations and structure prediction. We demonstrate that pressure serves as the primary driving force, whereas anion electronegativity regulates activation by tuning the Sr 4d band position, d-state delocalization, and p-d hybridization. The activation strength increases systematically with decreasing anion electronegativity, accompanied by pronounced electronic reconstruction and a charge-transfer reversal from Sr → Te to Te → Sr in Sr-Te at ∼400 GPa. Analysis of nine reported heavy alkali- and alkaline-earth-metal chalcogenide systems provides a qualitative comparison supporting the general trend of this anion-dependent regulation. These findings establish an anion-tunable framework for controlling orbital activation under extreme compression.