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 μ₃-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.