Driving forces for the phase transition of CuQ2-TCNQ molecular crystals. Issue 27 (2nd June 2016)

• Record Type: Journal Article
• Authors: Yu, Dehong; Kearley, Gordon J.; Liu, Guangfeng; Mole, Richard A.; McIntyre, Garry J.; Tao, Xutang
• Is Part Of: CrystEngComm. Volume 18:Issue 27(2016)
• Page Start: 5070
• Page End: 5073
• Publication Date: 2016-06-02
• Subjects: Crystals -- Periodicals; Crystal growth -- Periodicals; Crystallography -- Periodicals; Cristaux -- Périodiques; Cristaux -- Croissance -- Périodiques; Cristallographie -- Périodiques; 548
• DOI: 10.1039/c6ce00754f
• Languages: English
• ISSNs: 1466-8033

Abstract

Abstract : The interlayer π–π interaction is responsible for the coupling of different layers with dramatic changes in crystal orientations, while the strong intralayer hydrogen bonding maintains the integrity of layer structures upon phase transition. 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.