Now in Inorganic Chemistry @acs.org 📄! Collaboration with Nick and Liam from SSRL ⚠️ Treating of Mg(BH4)2 with liquid ammonia yields the hexammine (NH3)6Mg(BH4)2 whose structure was solved🔎 using radiation from SLAC. Congrats to the team NREL, @sandialabs.bsky.social ! pubs.acs.org/doi/10.1021/...
Hexammine magnesium borohydride, Mg(NH3)6(BH4)2, consists of adducted NH3 molecules locked in a matrix of Mg cations and borohydride anions. It is a candidate material for hydrogen storage, with 16.8 wt % hydrogen stored in both the NH3 and borohydride anions. It may also be of interest as an Mg2+-conducting electrolyte in solid-state batteries. Its crystal structure has, until now, eluded a proper structural solution due to ambiguity regarding the NH3 position and behavior. In this work, we show using synchrotron X-ray diffraction that the room-temperature structure can be solved only with a model assuming the orientational disorder of ammonia molecules within the crystal structure. Cooling the sample to 120 K yields additional Bragg peaks, which can be solved only with a unit cell expansion consistent with the freezing of the orientational freedom of ammonia molecules. Using this insight from the structure solution, we performed a full assignment of the vibrational modes in the room-temperature infrared spectrum.
