Fig. 7.
Dimensional cross-over reflected in changed angle and length of dimers. The temperature dependence of Cu–Cu bond lengths and tilt angles with respect to the a–b plane derived from neutron powder diffraction at high pressure. A symmetry change from C121 to P121 occurs at Tc = 122 K. (A) The relative ratio of the bond lengths of the red to the blue Cu–Cu dimers of Fig. 5B (solid squares) diverges from 1 for T < Tc, where all Cu–Cu dimers are no longer equivalent. (B) Tilting of the red and blue dimers out of the a–b plane below Tc.