Figure 1. Phase transitions of ZIF-4 on heating.

(a) Highlighting the rings and imidazolate linkages in zeolitic topologies, in the ordered structure of crystalline ZIF-4 (left) and ZIF-8 (center), and the disordered HDA phase (right) obtained by Molecular Dynamics modelling (Supplementary Methods). Zn, orange; N, blue; C, green; and H, grey. (b) Thermogravimetric analysis and C_p plots for ZIF-4 and ZIF-8, showing, for the former (inset), exothermic collapse to the LDA phase (1) which is closely followed by (2) endothermic formation of the HDA phase, and (3) recrystallization (exothermic). Endothermic melting (4) then follows before thermal degradation. (c) X-ray PDF data D(r) measured for the MQG (green), ZIF-4 (broken black) and the HDA phase (broken pink). The X-ray total scattering data S(q) is presented in Supplementary Fig. 1. Inset: optical images of (left) ZIF-4 (right) MQG, showing the typical fracture pattern of a non-metallic bulk glass. Scale bars, 100 μm.