Dynamic disorder, Strain and Sublimation of Crystalline Caged Hydrocarbons from First Principles

Abstract

Caged hydrocarbons exhibit diverse molecular and material properties thanks to a large variability of the three-dimensional carbon backbone of such molecules. High molecular symmetry of caged hydrocarbons predetermines these materials to pack very efficiently in crystal lattices that belong to highly symmetric space groups, as well as to easily form plastic solid phases with highly pronounced dynamic disorder in the vicinity of the melting temperature. This work aims at resolving the literature debate about the two contradictory values of experimental sublimation enthalpy for cubane, being a typical state of the art for such uncommon molecules. For this purpose, we use density functional theory (DFT) powered quasi-harmonic protocol, further fortified with the ab inito fragment-based calculation of the cohesive energy of crystalline cubane at the CCSD(T) level. Further, this work presents a viable first-principles treatment of dynamic disorder of molecules via their hindered rotations in the crystal lattice. A protocol for assessment of the energetic and entropic aspects of this local disorder, as well as to the related anharmonic contributions to the thermodynamic properties arising from these dynamic degrees of freedom is presented and validated. Finally, the question, whether the molecular steric strain is compensated by stronger crystal cohesion, is addressed.

First-Principles Models of Polymorphism of Pharmaceuticals: Maximizing the Accuracy-to-Cost Ratio

“…Such a computational setup has been extensively validated previously for various molecular crystals. 3,4,8,53 It will be termed PBE hereafter. More details on the computational setup are given in Table S3.…”

Orientational Disorder in Crystalline Disubstituted Benzenes and Its Implications for Sublimation and Polymorphism

“…To decipher how the local molecular interactions are affected by unit-cell perturbations, a fragment-based scheme was adopted. It identifies all pair interactions of a reference molecule in the crystal lattice within a certain cutoff, which was set to 4 Å in this case to focus on the first coordination shell only . Individual pair interaction energies were calculated in the Molpro software, version 2019.1, using the explicitly correlated dispersion-corrected MP2C-F12 method with the aug-cc-pVTZ basis set, established earlier as a reliable way for efficient calculations of noncovalent interactions …”

“…5 We also developed a first-principles methodology for modeling the anharmonic contributions of the dynamic disorder in molecular crystals. 26 In this work, four benzene derivatives, namely, 4ethynylbenzonitrile, 1-ethynyl-2-fluorobenzene, 1-ethynyl-4fluorobenzene, and 4-nitrobenzaldehyde, are selected for a case study of the impact of local static disorder on the thermodynamic properties and phase behavior of these molecular crystals. Except 1-ethynyl-4-fluorobenzene, all compounds were explicitly reported to form locally disordered crystals.…”

“…Recently, we illustrated that configurational entropy might be required within the quasi-harmonic ab initio predictions of relative stability of polymorphs of succinic and fumaric acid . We also developed a first-principles methodology for modeling the anharmonic contributions of the dynamic disorder in molecular crystals …”

Computational Exploration of the Thermal Rearrangement of Basketene: One Forbidden versus Two Allowed Pericyclic Reactions

“…As computer hardware and algorithms advance and play an increasingly indispensable role, density functional theory (DFT) and wavefunction methods have been widely applied to provide probative evidence for mechanism studies and, specially, to determine between stepwise and concerted pathways . Although various experimental and computational studies have been performed on (CH) 10 hydrocarbons recently, , none involved a study of the rearrangement mechanism. We now report a computational study of the thermal rearrangement of basketene to Nenitzescu’s hydrocarbon using DFT (M06-2X and ωB97X-D) and DLPNO–CCSD(T) to determine the favored mechanism and how strain and orbital symmetry factors influence the mechanism.…”