Department of Materials Science & Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS (UK).
Diamond Light Source Ltd. Diamond House, Harwell Science & Innovation Campus, Didcot, Oxfordshire, OX11 0DE (UK).
Angew Chem Int Ed Engl. 2015 May 26;54(22):6447-51. doi: 10.1002/anie.201410167. Epub 2015 Apr 14.
Desolvated zeolitic imidazolate framework ZIF-4(Zn) undergoes a discontinuous porous to dense phase transition on cooling through 140 K, with a 23 % contraction in unit cell volume. The structure of the non-porous, low temperature phase was determined from synchrotron X-ray powder diffraction data and its density was found to be slightly less than that of the densest ZIF phase, ZIF-zni. The mechanism of the phase transition involves a cooperative rotation of imidazolate linkers resulting in isotropic framework contraction and pore space minimization. DFT calculations established the energy of the new structure relative to those of the room temperature phase and ZIF-zni, while DSC measurements indicate the entropic stabilization of the porous room temperature phase at temperatures above 140 K.
脱溶剂沸石咪唑酯骨架 ZIF-4(Zn) 在冷却至 140 K 时经历了非连续的多孔到致密相转变，单元细胞体积收缩了 23%。低温非多孔相的结构是通过同步辐射 X 射线粉末衍射数据确定的，其密度略低于最密集的 ZIF 相 ZIF-zni。相转变的机制涉及到咪唑配体的协同旋转，导致各向同性的骨架收缩和孔隙空间最小化。DFT 计算确定了新结构相对于室温相和 ZIF-zni 的能量，而 DSC 测量表明在 140 K 以上温度下多孔室温相的熵稳定化。
