Phase transition between cubic and monoclinic polymorphs of the tetracyanoethylene crystal: the role of temperature and kinetics

Abstract

Prediction of the relative stabilities and phase transition behavior of molecular crystalline polymorphs is highly coveted as distinct phases can possess different physical and chemical properties while having similar energies. Crystalline tetracyanoethylene (TCNE, C 6 N 4 ) is known to exhibit rich solid state phase behavior under different thermodynamic conditions, as demonstrated by a wealth of experimental studies on this system. Despite this fact, the role of temperature and kinetics on the phase diagram of TCNE remains poorly understood. Here, first-principles calculations and highresolution Fourier-transformed infrared (HR-FTIR) spectroscopy experiments are used to study the relative stabilities of the cubic and monoclinic phases of TCNE as a function of temperature. Specifically, density-functional theory with the van der Waals interactions method of Tkatchenko and Scheffler (DFT+vdW) is employed. The accuracy of this approach is demonstrated by the excellent agreement between the calculated and experimental structures. We find that the cubic phase is the most stable polymorph at 0 K, but becomes less favorable than the monoclinic phase at 160 K. This temperature-induced phase transition is explained on the basis of varying close contacts and vibrational entropies as a function of temperature. These findings are supported by a temperaturedependent HR-FTIR linewidth study of the CMN vibrons.

First‐principles modeling of molecular crystals: structures and stabilities, temperature and pressure

“…Furthermore, it was shown by Reilly and Tkatchenko that a high‐level vdW‐inclusive DFT method is able to describe the relative enthalpy and entropy of the two known polymorphs of aspirin correctly, offering a resolution for a long‐standing controversy regarding the metastability of form‐II aspirin . In addition, Schatschneider et al have shown that vdW‐inclusive DFT is able to describe temperature‐induced phase transitions between molecular crystal polymorphs of tetracyanoethylene in excellent agreement with experimental data …”

Electrosteric colloidal stabilization for obtaining SrTiO3/TiO2 heterojunction: Microstructural evolution in the interface and photonics properties

“…However, these works are related to single phase materials and not for heterojunctions with interface formed with different chemical compounds, phases and crystalline lattices tensions. It has been reported in several works that physical chemistry parameters deriving from growth surface between materials [18] and from synthesis procedure [19,20] can promote changes in crystalline phase stability, and hence changes on energy emission behavior. Different synthesis have been proposed in order to modulate the heterostructure properties, but, traditional methods are generally complex [10,14,21,22].…”

Many‐Body Dispersion Interactions in Molecular Crystal Polymorphism

“…To incorporate these long‐range electron correlation effects within DFT, significant progress has been made by using the standard C 6 / R 6 pairwise additive expression for the dispersion energy 5–7. Indeed, DFT with pairwise dispersion terms can yield accurate results when the energy differences between molecular crystal polymorphs are sufficiently large 8–10. Notably, Neumann et al.…”