Browsing by Author "Bridgeman, AJ"

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    Elucidating negative thermal expansion in MOF-5
    (American Chemical Society, 2010-9-09) Lock, N; Wu, Y; Christensen, M; Cameron, L; Peterson, VK; Bridgeman, AJ; Kepert, CJ; Iversen, BB
    Multi-temperature X-ray diffraction studies show that twisting, rotation, and libration cause negative thermal expansion (NTE) of the nanoporous metal−organic framework MOF-5, Zn4O(1,4-benzenedicarboxylate)3. The near-linear lattice contraction is quantified in the temperature range 80−500 K using synchrotron powder X-ray diffraction. Vibrational motions causing the abnormal expansion behavior are evidenced by shortening of certain interatomic distances with increasing temperature according to single-crystal X-ray diffraction on a guest-free crystal over a broad temperature range. Detailed analysis of the atomic positional and displacement parameters suggests two contributions to cause the effect: (1) local twisting and vibrational motion of the carboxylate groups and (2) concerted transverse vibration of the linear linkers. The vibrational mechanism is confirmed by calculations of the dynamics in a molecular fragment of the framework. © 2010, American Chemical Society