Driving forces for the phase transition of CuQ2-TCNQ molecular crystals
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Date
2016-05-23
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Royal Society of Chemistry
Abstract
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
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Keywords
Phase transformations, Inelastic scattering, Molecular dynamics method, Density functional method, Enthalpy, Hydrogen, Phase transformations
Citation
Yu, D., Kearley, G. J., Liu, G., Mole, R. A., McIntyre, G. J., & Tao, X. (2016). Driving forces for the phase transition of CuQ2-TCNQ molecular crystals. CrystEngComm, 18(27), 5070-5073. doi:10.1039/C6CE00754F