Crystalline thiophene—I: Phase diagram and structures of two orientationally disordered crystalline phases. crystallographic evidence for a metastable low temperature phase

doi:10.1016/0022-3697(84)90035-0

Journal of Physics and Chemistry of Solids

Volume 45, Issue 3, 1984, Pages 299-309

https://doi.org/10.1016/0022-3697(84)90035-0 Get rights and content

Abstract

The first order phase diagram of thiophene has been determined from 217.5 to 298 K up to 4̃00 MPa. It shows that a high pressure phase which melts at room temperature is in fact Waddington et al.'s atmospheric pressure phase II and discloses a ∼R ln2 entropy increment at the II→I phase transition. The structures of phases I and II have accordingly been investigated taking this relationship into account. For phase I, the best result is obtained for space group Cmca with 20 equiprobable molecular orientations. This leads us to assume that phase II is better described by space group Pnma with 10 molecular orientations. Finally, a metastable phase I′ can easily be obtained by cooling phase I at atmospheric pressure. Its unit cell is derived from that of I by multiplying parameter b by 2 and parameter c by 20: this can be considered as an a posteriori justification of the multiple-of-five number of molecular orientations in phases I and II.

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The Physics of High Pressure

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These indicate that the rate of the HNB crystal growth is affected strongly by the presence of phenyl ring(s) within molecule. In this respect, it is noticed that benzene and thiophene molecules are known to aggregate in the liquid as well as crystalline state so as to place the phenyl (or thiophene) rings perpendicularly to one another among the nearest neighbors [17–22], as shown in Fig. 10. The C–H⋯π(electron) interaction, being a kind of weak hydrogen bond, is expected to stabilize energetically the arrangement of the molecules [23].
Low-temperature crystal growth was investigated in the fragile liquids of iso-propylbenzene, dimethylphthalate, diphenylphthalate, and 2-methyltetrahydrofuran by using an optical microscope. Homogeneous-nucleation-based (HNB) crystal growth was observed to proceed in the supercooled liquids of the former three substances around and below their glass-transition temperatures, as in the cases of o-terphenyl, toluene, and other fragile liquids, but not detected in 2-methyltetrahydrofuran. Thus far, the growth has been observed only for the substances possessing phenyl group(s) in the molecule. The maximum rates of the growth were found to decrease with increasing the size of substituents to the phenyl ring(s). It was concluded from this fact that the C–H⋯π(electron) intermolecular interaction between phenyl rings enhances to generate an ordered region required for the crystal nucleation and thereby the HNB crystal growth. Among all the observations of the HNB growth, a rough relation was found that the maximum growth rate increases with an increasing maximum-rate temperature normalized by the respective glass transition temperatures.
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Deuterated thiophene has been studied by powder neutron diffraction spectroscopy from ∼ 60 K to melting temperature. Preliminary DSC measurements have shown that the thermodynamic behaviours of hydrogenated and deuterated thiophene are almost identical, so that the conclusions drawn from the present structural studies of C₄D₄S are valid for both compounds. The structures of stable phases IV and V have been observed for the first time: phase V lattice is obtained by multiplying by 2 parameter c of orthorhombic phase III and has been assigned space group P2₁ma; phase IV also corresponds to a superstructure of phase III, but, as expected because of the quasi-fivefold molecular symmetry and of its reorientational dynamics, it can be thought to be an incommensurate phase.
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Heat capacities of thiophene-benzene binary solutions [(1−x)C₄H₄S+xC₆H₆] with x = 0.199, 0.404 and 0.601 were measured by an adiabatic calorimeter in the temperature range 13–300 K. The results are presented in the form of phase diagrams in the thiophene-rich region and over the whole concentration range. The change in temperature, size, and shape of the heat capacity anomalies occasioned by the composition variation indicated that, for this system, changes in molecular environment exerted considerable effects on the phase and glass transitions of pure thiophene. Calculated solidus and liquidus lines based on Raoult's law showed that a considerable deviation from ideal mixing occurred in either or both of the solid and liquid solutions. The calorimetric entropy of each solid solution was calculated to derive a possible residual entropy arising from frozen-in processes in the system.
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Crystalline thiophene—I: Phase diagram and structures of two orientationally disordered crystalline phases. crystallographic evidence for a metastable low temperature phase

Abstract

J. Appl. Cryst.

Bull. Soc. Franc. Miner. Crist.

J. Raman Spectr.

J. Am. Chem. Soc.

High Temp. High Press.

High Temp. High Press.

Thèse de Doctorat

Acta Cryst.

J. Chim. Phys.

J. Am. Chem. Soc.

Acta Cryst.

Bull. Soc. Chim. Belg.

The Physics of High Pressure