Reversible Dissociation for Effective Storage of Diborane Gas within the UiO-66-NH 2 Metal-Organic Framework.

There is an acute need for materials that can store the toxic and highly reactive diborane gas at room temperature. In this work, the interfacial chemistry leading to safe and reversible storage of diborane (B 2 H 6 ) in the UiO-66-NH 2 metal-organic framework (MOF) was investigated via in situ transmission infrared (IR) spectroscopy, temperature-programmed desorption (TPD), and electronic structure calculations. The infrared spectrum of B 2 H 6 adsorbed within UiO-66-NH 2 indicates hydrogen bonding with the μ 3 -OH groups of the MOF nodes and chemisorption at the -NH 2 groups of the MOF linkers. The conversion of physisorbed to chemisorbed diborane, as observed through a spectroscopically unique intermediate species, occurred over a broad temperature regime from 80 to 410 K. During B 2 H 6 -TPD studies, both the weakly and strongly bound species were found to desorb exclusively as molecular B 2 H 6 . Infrared spectroscopic studies, performed during diborane adsorption and reaction, combined with electronic structure calculations, revealed that chemisorption occurred via a reversible dissociation reaction involving a "half-open" B 2 H 6 intermediate and resulted in the formation of two NH 2 -bound BH 3 units, which leave the MOF as B 2 H 6 via recombinative desorption. The close spacing of -NH 2 groups in the UiO-66-NH 2 MOF is key to enabling high-temperature chemisorptive storage of B 2 H 6 , and the spatial arrangement of the amine groups has a significant effect on the dissociation energy profile. This work demonstrates that reversible dissociation of B 2 H 6 on precisely engineered, nucleophile-rich materials represents a promising pathway to diborane stabilization and long-term storage.