“…The observation of such complex phase behaviour has been attributed to the fact that high-pressure forces electron density to order in less conventional ways to accommodate the pressure-induced reduction in volume, and hence minimize the impact of the pV contribution to the enthalpy of the system. A limited number of other elemental metals (Porsch & Holzapfel, 1993), as well as peroskites and pure inorganics (Kabbour et al, 2012;Downie et al, 2013;Brinkmann et al, 2004), have been show to display pressure-induced re-entrant phase behaviour, defined by Dove as a transition where there is a sequence of two phase transitions, with the first and third phases having the same symmetry and effectively identical structures (Dove, 2011). In molecular solids, such transitions are exceptionally rare, with only two well-known purely structural examples, namely rochelle salt and malonitrile (Levitskii et al, 2010;Beevers & Hughes, 1941;Suzuki & Shiozaki, 1996;David et al, 2013;Dove & Rae, 1983;Wasiutynski et al, 1987;Dove, 2011).…”