Dihydrogen Bonding under High Pressure: A Raman Study of BH3NH3 Molecular Crystal

The effects of high pressures (up to 40 kbar) on the dihydrogen-bonded BH 3 NH 3 molecular crystal were investigated using Raman spectroscopy in diamond and moissanite anvil cells. The stretching mode frequencies of the NH 3 proton donor groups exhibited moderate red shifts with increasing pressures, as found in many conventional hydrogen-bonded systems of weak to medium strength. The stretching modes corresponding to the BH 3 proton acceptor group, on the other hand, showed large blue shifts with increasing pressure, which, however, are not related to the changes in the N−H···H−B interactions. The BH 3 NH 3 crystals undergo a pressure-induced disorder−order phase transition around 8 kbar, which is facilitated by the presence of dihydrogen bonds.