Reversible Dissociation for Effective Storage of Diborane Gas within the UiO-66-NH2 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 (B2H6) in the UiO-66-NH2 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 B2H6 adsorbed within UiO-66-NH2 indicates hydrogen bonding with the mu(3)-OH groups of the MOF nodes and chemisorption at the -NH2 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 B2H6-TPD studies, both the weakly and strongly bound species were found to desorb exclusively as molecular B2H6. 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" B2H6 intermediate and resulted in the formation of two NH2-bound BH3 units, which leave the MOF as B2H6 via recombinative desorption. The close spacing of -NH2 groups in the UiO-66-NH2 MOF is key to enabling high-temperature chemisorptive storage of B2H6, and the spatial arrangement of the amine groups has a significant effect on the dissociation energy profile. This work demonstrates that reversible dissociation of B2H6 on precisely engineered, nucleophile-rich materials represents a promising pathway to diborane stabilization and long-term storage.