Pressure-Induced Polymorphic Transitions in Crystalline Diborane Deduced by Comparison of Simulated and Experimental Vibrational Spectra

Abstract

We investigate and assign the pressure-induced structural transformations in crystalline diborane (B 2 H 6 ) observed spectroscopically by Song and co-workers (J.

Pressure-induced phase transition in hydrogen-bonded molecular crystal acetamide: combined Raman scattering and X-ray diffraction study

“…It is worth noting that the mode marked by a solid circle shows red shift at 3.2 GPa, which can be explained as the increased bond length and smaller chemical force constant induced by pressure. 50 The evolution of the internal modes versus pressure in the range of 400-1800 cm -1 is depicted in Fig. 4(b), most of the internal modes show increasing frequencies when pressure is increased, and discontinuities are observed at 0.9 and 3.2 GPa, which is consistent with the changes in Raman spectra, suggesting the structural changes.…”

“…With increasing pressure, most of internal modes shift gradually toward higher frequencies due to the decrease in bond lengths and increase in effective force constants. 50 However, remarkable changes are observed at 0.9 GPa. For example, the two modes marked by arrows (0.3 GPa) around 582 cm -1 related to the deformation of N-C=O show obvious variation in intensity.…”

The Search for Superconductivity in High Pressure Hydrides

“…211,212 The computed IR and Raman spectra of ten candidate phases that contained the molecular diborane unit were compared with those obtained experimentally. 216 This study showed that phase I corresponds to the β-diborane structure, and the best candidates for phases II and III possessed a P 2 1 /c symmetry lattice, but with different molecular orientations. Importantly, all of the experimental data was consistent with phases containing B 2 H 6 units, suggesting that transformation to the thermodynamically preferred products, cyclic oligomers and polymer chains, is kinetically hindered.…”

“…Early theoretical studies concluded that molecular boranes become thermodynamically unstable towards systems comprised of extended bonded networks by ∼100-300 GPa, and that a BH 3 analogue of AlH 3 would become metallic below 30 GPa. 215 Twenty years later DFT calculations 213,216 were carried out to help characterize the phases investigated in Refs. 211,212 The computed IR and Raman spectra of ten candidate phases that contained the molecular diborane unit were compared with those obtained experimentally.…”

A theoretical study of the spectroscopic properties of B2H6 and of a series of BHyz−species (x = 1−12, y = 3−14, z = 0−2): From BH3 to B12H

“…Diborane, B 2 H 6 [61], is the simplest stable borohydride at ambient condition [62]. It has a ring-type molecular structure and has two-bridging hydrogens [63] (see Figure 1). Begue [64] used high-level calculations to investigate the anharmonic vibrational properties of this compound.…”