Hydrogen Encapsulation in a Silicon Clathrate Type I Structure:  Na 5.5 (H 2 ) 2.15 Si 46 :  Synthesis and Characterization (original) (raw)

A hydrogen-encapsulated inorganic clathrate, which is stable at ambient temperature and pressure, has been prepared in high yield. Na5.5(H2)2.15Si46 is a sodium-deficient, hydrogen-encapsulated, type I silicon clathrate. It was prepared by the reaction between NaSi and NH4Br under dynamic vacuum at 300°C. The Rietveld refinement of the powder X-ray diffraction data is consistent with the clathrate type I structure. The type I clathrate structure has two types of cages where the guest species, in this case Na and H2, can reside: a large cage composed of 24 Si, in which the guest resides in the 6d crystallographic position, and a smaller one composed of 20 Si, in which the guest occupies the 2a position. Solid-state 23 Na, 1 H, and 29 Si MAS NMR confirmed the presence of both sodium and hydrogen in the clathrate cages. 23

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