Pressure-induced complexation of NH3BH3-H2

High pressure Raman spectroscopy of NH3BH3-H-2 mixtures up to 60 GPa reveals unusual pressure-induced complexation and intermolecular interactions. Stretching modes of H-2 in the complex arise at 6.7 and 10 GPa, increasing in frequency with pressure of up to 60 GPa with different pressure coefficients, and at similar to 40 GPa, the lower frequency mode approaches vibron frequency of bulk H-2. Pressure-induced transformations in pure NH3BH3 studied up to 60 GPa reveal a disorder-order transition at 1 GPa (phase II) and further transitions at 5 (phase III) and 10 GPa (phase IV). The spectra of both pure NH3BH3 and the NH3BH3-H-2 complex provide evidence for strengthened of the N-H delta+center dot H delta--B dihydrogen bonding linkages up to 50 GPa, beyond which they weaken. The dihydrogen bonding breaks down due to interactions with H-2 between 15 and 20 GPa in the NH3BH3-H-2 complex. The behavior of the nu(NH3) modes in the NH3BH3-H-2 complex indicates a dominant role of the NH3 functional group in the observed interactions.