Michael A. Leech, Judith A. K. Howard, Slimane Dahaoui, Nayan K. Solanki and Malcolm A. Halcrow
The complex [Cu{2,6-di(pyrazol-1-yl)pyridine}2](BF4)2 undergoes a solid-state phase transition at 41 K, involving the cooperative ordering of its planar dynamic pseudo-Jahn–Teller system; this unique phase transition is characterised by single-crystal X-ray diffraction techniques, employing an open-flow helium cryostat.