Perspective view of the thiourea pyridinium iodide inclusion compound at . Thiourea molecules form channel in which cations stack. Anions are at the edge of the channels (Ref. 26).
Temperature dependencies of the specific heat (left axis) and the entropy (right axis).
Evolution of the diffracted intensity in the reciprocal plane between the HT and LT phases. The symmetry breaking, associated with the change from a to unit cell, is characterized by the appearance of numerous peaks (inside the circles) indexed at LT.
Temperature dependence of the intensity of some Bragg reflections associated with the symmetry breaking , clearly indicating a second order phase transition around . A power-law fit of the intensities performed in the vicinity of the phase transition as , gave . The lines below are guide for the eyes.
Temperature dependencies of the lattice parameters , , and and of the volume V for which weak anomalies are observed at .
The scheme of the thiazolium cation and the direction of the dipole moment. The molecular sites correspond to a statistical chemical disorder of the two orientations, as molecules are located on a symmetry plane.
View along at (top, left) and (top, right) and along at (bottom left) and (bottom right) showing the relative rotation and translation of the thiazolium cations from one channel to another one and related to the symmetry breaking from to unit cell. It is accompanied by a deformation of the thiourea ribbons. The top views correspond to a slice of the structure (rectangle in bottom figures).
View along the direction at (left) and (right). The vertical axis is . The rotation of 180° of the cations between the different channels at LT also modifies the short contacts values between H of the guest and Br of the host in the different channels in the LT phase.
The thermal ellipsoids of thiourea molecules at indicating out of plane motion. For clarity, hydrogen atoms are omitted.
Permittivity [(a) and (c)] and loss tangent [(b) and (d)] in in the different frequency ranges. The vertical dot lines indicate the phase transition.
The correlation time obtained from dielectric spectroscopy [(◻) frequency range of ; (◼) frequency range of ] and from spin-lattice relaxation times (——) and (----) . The vertical dot line indicates the phase transition.
The temperature dependences of NMR second moment for . The vertical dot line indicates the phase transition.
The temperature dependences of spin-lattice relaxation time at (◼) and relaxation time in the rotating frame at (▲) and (○) . The solid lines are theoretical fits. The vertical dot line indicates the phase transition.
The schematic view of the thiazolium cation (a) and thiourea molecules (b) showing the possible motions about the different axes.
Crystal data and structure refinement measured at 250 and . CCDC reference numbers are 689075 and 689076.
The fit activation parameters and values obtained for .
The experimental and simulated values of the second moment for
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