Dynamics in molecular and molecular-ionic crystals: A combined experimental and molecular simulation study of reorientational motions in benzene, pyridinium iodide, and pyridinium nitrate

Abstract

Molecular dynamics (MD) simulations for crystalline benzene (C(6)H(6)), pyridinium iodide [C(5)NH(6)](+)I(-), and pyridinium nitrate [C(5)NH(6)](+)NO(3)(-) have been performed as a function of temperature and pressure. Despite the similar shape of the benzene molecule and the pyridinium cation, the experimental and simulated data have showed clear differences in their dynamics. Therefore, the rotational dynamics have been explored in detail by comparing thoroughly the existing experimental results together with new quasielastic neutron scattering (QENS) data obtained for (PyH)NO(3) and molecular dynamics simulations. The correlation times, activation energy, geometry of motion of benzene molecule and pyridinium cation, isothermal compressibility, and activation volume obtained from the simulations are compared with the experimental results obtained by nuclear magnetic resonance and QENS methods. MD simulations have also revealed that reorientation of the pyridinium cation in pyridinium nitrate between two inequivalent positions is strongly affected by the hydrogen bond N-H···O between the cation and the anion and the influence of temperature on strength of the hydrogen bond is much more important than that of the pressure.

Internal Vibrations of Pyridinium Cation in One-Dimensional Halide Perovskites and the Corresponding Halide Salts

“…Upon heating from cryogenic to room temperature, these materials undergo an order–disorder phase transition from the monoclinic to the rhombohedral phase, in which the previously frozen PyH + cations begin to rotate around the pseudo-six-fold axis (“C 6 ”) ( Figure 1 c) [ 37 , 38 , 39 ]. The order–disorder phase transitions and molecular motions of the PyH + cation in various compounds have been studied [ 36 , 37 , 38 , 39 , 40 , 44 , 45 , 46 , 47 ]. Pyridinium internal vibrational modes are shown to be sensitive to such phase transitions [ 48 , 49 , 50 , 51 ].…”

“…Of particular interest is the movement of the simple aromatic pyridinium cation PyH + = C 5 H 5 NH + , which stabilizes both perovskite-like compounds and PyHX (X − = I − , Br − ) salts [ 36 , 37 , 38 , 39 , 40 ]. The hybrid halide perovskites PyPbX 3 (X − = I − , Br − ) have the 1D structure of face-shared octahedra chains [ 31 , 32 , 41 , 42 ].…”

Unravelling guest dynamics in crystalline molecular organics using solid-state NMR and molecular dynamics simulation

“…DMSO molecules have been observed to rotate through 180° in MD simulations of a DMSO solvate of carbamazepine, allowing the experimental crystallographic data to be rationalised 28 . MD simulations have been used in a similar way to rationalise experimental data on the dynamics of pyridinium cations obtained from quasi-elastic neutron scattering [29][30][31] , and 19 F NMR relaxation data observing molecular motion in solid octafluoronaphalene 32 .…”