Ice-thirteen (Ice XIII)
Ice-thirteen (ice XIII) is the proton-ordered form of ice-five (shown opposite), formed by doping with HCl below 130K and at 500 MPa to facilitate the phase transition . A reversible transition between ice XIII and (metastable) ice V is observed on cycling between 80 and 120 K . The crystals were monoclinic P21/a with cell
dimensions a 9.24 Å, b 7.47 Å and c 10.30 Å (90°,
109.7°, 90°, 28 molecules; at atmospheric pressure
and 80 K) and a unit cell contains 28 water molecules (four each of seven distinct types) .
Interactive Jmol structure is given.