Ship-in-a-Bottle Synthesis of High Concentration of N₂ Molecules in a Cage-Structured Electride

We report the formation of neutral nitrogen molecules in the cages of [Ca₁₂Al₁₄O₃₂]²⁺ (C12A7) framework compensated by extra-framework anions. NH₃ treatment of C12A7 electride (C12A7:e^-) at 800 °C leads to the formation of N₂ and NH^2- species in the C12A7 cages. N₂ and NH species in the cages are identified using the Raman spectroscopy of ¹⁴NH₃ and ¹⁵NH₃-treated C12A7:e^-. The concentration of H and N in the C12A7 cages after NH₃ treatment is ∼10²¹ cm^-3. We propose a two-step mechanism, supported by density functional theory (DFT) modeling, of N₂ incorporation into the C12A7 cages, i.e., incorporation of NH^2- formed from decomposition of NH₃ at C12A7:e^- surface followed by the NH^2- species reacting to form N₂ molecules. Encapsulation of neutral molecules, as opposed to negatively charged species reported in C12A7 previously, offers new opportunities for trapping and storing gaseous substances in nanoporous materials.