Ferrimagnetic Cage Framework in Ca12Fe10Si4O32Cl6.

The positively charged cage framework of the natural mineral mayenite, which enables various species with negative charge to be stabilized, is one of the key structures to provide the new functionalities exploited in applications. Here we report the structural and magnetic properties of recently found eltyubyuite, Ca12Fe10Si4O32Cl6, which is the first compound bearing a transition metal oxide as a main constituent in the mayenite-type structure. From neutron powder diffraction measurements at T = 20 K and the low temperature Mössbauer measurement, we determined the magnetic structure of eltyubyuite to be a ferrimagnet with oppositely aligned magnetic moments of +3.17(3) and -3.05(8) µB in two tetrahedral Fe sites with different oxygen ligands, all bridging oxygens or mixed bridging and nonbridging oxygens. As far as is known, this result is likely to be a first example showing ferrimagnetism stemming from only tetrahedral Fe3+ ions. The reduced magnetic moment per Fe3+ and the resultant small net moment per unit cell of 22 µB at µ0H = 5 T and T = 15 K are attributed to strong covalency in much shorter Fe-O bonds in the FeO4 tetrahedra.

Electron anions and the glass transition temperature.

Properties of glasses are typically controlled by judicious selection of the glass-forming and glass-modifying constituents. Through an experimental and computational study of the crystalline, molten, and amorphous [Ca12Al14O32](2+) ⋅ (e(-))2, we demonstrate that electron anions in this system behave as glass modifiers that strongly affect solidification dynamics, the glass transition temperature, and spectroscopic properties of the resultant amorphous material. The concentration of such electron anions is a consequential control parameter: It invokes materials evolution pathways and properties not available in conventional glasses, which opens a unique avenue in rational materials design.

NH(2-) dianion entrapped in a nanoporous 12CaO·7Al2O3 crystal by ammonothermal treatment: reaction pathways, dynamics, and chemical stability.

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 NH(2-), can be incorporated into the nanocages of the mayenite crystals, [Ca24Al28O64](4+)(e(-))4 and [Ca24Al28O64](4+)(O(2-))2, by ammonothermal treatment. We evaluated the reaction conditions and found that the anion exchange reaction proceeded at higher than 500 °C. Raman spectroscopy showed that the N-H band position of encaged NH(2-) was close to that of CaNH and MgNH crystals. We also studied the reaction pathways that yield NH2(-) and NH(2-) anions and their dynamic motions by (1)H NMR spectroscopy. Successive reactions of encaged e(-) and O(2-) ions with NH3 yielded NH2(-), NH(2-), and H(-) or OH(-), in which the O(2-) ion reacted more efficiently with NH3. The maximum NH(2-) concentration and content were ∼2.7 × 10(20) cm(-3) and ∼0.25 (wt %)NH, respectively. The short spin-lattice relaxation time found in (1)H NMR suggests that the incorporated NH2(-) and NH(2-) rotate or librate in the cage near room temperature. Stability tests showed that the encaged NH(2-) 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 NH(2-) desorbed as NH3 at higher than 500 °C under vacuum (Ea = 172 kJ mol(-1)). It is thus expected that C12A7:NH(2-) will function as a reactive nitrogen source for nitrogen transfer reactions by in situ cage degradation.