Porous and Dense Magnesium Borohydride Frameworks: Synthesis, Stability, and Reversible Absorption of Guest Species

Abstract

A highly porous form of Mg(BH4)2 (see picture; Mg green, BH4 blue, unit cells shown in red) reversibly absorbs H2, N2, and CH2Cl2. At high pressures, this material transforms into an interpenetrated framework that has 79 % higher density than the other polymorphs. Mg(BH4)2 can act as a coordination polymer that has many similarities to metal–organic frameworks

Fast carbon dioxide recycling by reaction with γ-Mg(BH4)2

“…1 Among them, gamma phase of Mg(BH 4 ) 2 possesses the interesting peculiarity to show a large permanent porosity, accounting for about the 33% of the material volume (see Fig. 1).…”

“…1). 1 Its structure is constituted by Mg 2+ ions in tetrahedral coordination, linked through a shared [BH 4 ] -, giving rise to an highly 3D porous structure characterized by hexagonal overtures with a narrowest dimension of 5.95 Å (geometrical distance). Each hexagon, having a chair conformation, shares every Mg-BH 4 -Mg side with a vicinal hexagon through a tetrahedral angle.…”

Characterization of Gas‐Solid Reactions using In Situ Powder X‐ray Diffraction

“…The molecules interact with the BH 4 -units in the structure, thus revealing new physisorption interactions. [10] Gas adsorption was successfully investigated by in situ SR-PXD heating a closed, isobar sample container. The isosteric heats of adsorption of nitrogen and hydrogen in γ-Mg(BH 4 ) 2 were determined from in situ SR-PXD data to be Q st (N 2 ) ≈ 15 kJ mol -1 and Q st (H 2 ) ≈ 6 kJ mol -1 (average values) and Q st Ͼ 7 kJ mol -1 at a loading of 15 mg H 2 g -1 .…”

“…position of adsorbed gas molecules. [10] . Additionally, information of thermodynamic and kinetic data of gas release and uptake can be extracted.…”

“…[9] In situ SR-PXD has proven superior to any other technique as it simultaneously probes the exact host-guest interactions, provides information on the amount of gas physisorbed as a function of pressure and temperature and in some cases simultaneously thermodynamic data such as the isosteric enthalpy of adsorption. [10] …”