NH2- Dianion Entrapped in a Nanoporous 12CaO center dot 7Al(2)O(3) Crystal by Ammonothermal Treatment: Reaction Pathways, Dynamics, and Chemical Stability

作者：Hayashi Fumitaka^*; Tomota Yudai; Kitano Masaaki; Toda Yoshitake; Yokoyarna Toshiharu; Hosono Hideo

来源：Journal of the American Chemical Society, 2014, 136(33): 11698-11706.

DOI：10.1021/ja504185m

Inorganic imides are useful for hydrogen storage and base-catalyzed reactions but are extremely unstable under ambient conditions, which hinders their practical use as functional materials. Here, we demonstrate that NH2- and H-, as well as NH2-, can be incorporated into the nanocages of the mayenite crystals, [Ca24Al28O64](4+)(e(-))(4) and [Ca24Al28O64](4+)(O2-)(2), by ammonothermal treatment. We evaluated the reaction conditions and found that the anion exchange reaction proceeded at higher than 500 degrees C. Raman spectroscopy showed that the N-H band position of encaged NH2- was close to that of CaNH and MgNH crystals. We also studied the reaction pathways that yield NH2- and NH2- anions and their dynamic motions by H-1 NMR spectroscopy. Successive reactions of encaged e(-) and O2- ions with NH3 yielded NH2-, NH2-, and H- or OH-, in which the O2- ion reacted more efficiently with NH3. The maximum NH2- concentration and content were similar to 2.7 X 10(20) cm(-3) and similar to 0.25 (wt %)(NH), respectively. The short spin-lattice relaxation time found in H-1 NMR suggests that the incorporated NH2- and NH2- rotate or librate in the cage near room temperature. Stability tests showed that the encaged NH2- ions are chemically stable under ambient conditions and in organic solvents. These results are attributed to the encapsulation of active anions within subnanometer-sized cages composed of Ca-O-Al oxide frameworks. The encaged NH2- desorbed as NH3 at higher than 500 degrees C under vacuum (E-a = 172 kJ mol(-1)). It is thus expected that C(12)A(7):NH2- will function as a reactive nitrogen source for nitrogen transfer reactions by in situ cage degradation.

• 出版日期2014-8-20