Fig. 2: Evidence of CN– flips in Cd(CN)2.
a Intensity map of the temperature-dependent neutron powder diffraction pattern of 114Cd(CN)2, showing the existence of a phase transition at Tc = 130 K. b Rietveld fits to the diffraction pattern at representative temperatures above (top, \({Pn}\bar{3}m\)) and below (bottom, \(I{4}_{1}/{amd}\)) Tc. Data are shown in black, fits in red, difference in grey and reflection positions as blue vertical bars. The contribution from a minor Hg(CN)2 impurity39 is indicated by asterisks. c Representation of the \(I{4}_{1}/{amd}\) crystal structure of Cd(CN)2 at 10 K: Cd atoms are shown in green, C in white, and N in black. Thermal ellipsoids (isotropic) are shown at 50% probability. d Temperature evolution of the spontaneous strain (red circles) and long-range CN– orientational order (black circles) determined by Rietveld refinement; error bars denote the standard errors obtained from refinement and, for the strain, are smaller than the symbols. The emergence of CN– order implies that CN– flips occur. The divergence of the strain and orientational order parameters marks a glass transition at Tg \(\simeq\) 80 K. e Contour plot of the 113Cd EXSY spectrum of natural-abundance Cd(CN)2 at 60 °C showing the correlation between resonances collected before (subscript ‘i’) and after (subscript ‘f’) a mixing period of 1 s. Intensities are scaled relative to the maximum value, and contour levels are indicated on the accompanying colour spectrum. The existence of off-diagonal correlations proves the activation of CN– flips, such as those which interconvert CdC3N and CdC2N2 coordination environments (marked).
