Browsing by Author "Tao, X"

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    Driving forces for the phase transition of CuQ2-TCNQ molecular crystals
    (Royal Society of Chemistry, 2016-05-23) Yu, DH; Kearley, GJ; Liu, G; Mole, RA; McIntyre, GJ; Tao, X
    The driving forces for the phase transition and relative stability of the two forms of CuQ2-TCNQ molecular crystals have been studied using inelastic neutron scattering (INS), density functional theory (DFT), and Hirshfeld surface analysis. DFT molecular dynamics (MD) simulations show that form-II has a lower enthalpy, but with increasing temperature form-I becomes thermodynamically stable due to the greater entropy. INS and MD simulations both show that the entropy of the hydrogen-bond network that holds molecules together within layers is higher in form-I. The interlayer π–π interactions are also weaker in form-I, leading to an overall “loosening” of the structure. The phase transition is kinetically hindered by the requirement to re-optimize the orientation of the layers. The strong H-bond interactions keep the in-plane atomic arrangement stable, while the weak interlayer π–π interactions provide the coupling between layers during the phase-transition. This subtle interplay of the two interactions maintains the integrity of the crystal upon phase transition even with dramatic physical dimension changes. © The Royal Society of Chemistry 2016