Local structure and dynamics of benzene confined in the IRMOF-1 nanocavity as studied by molecular dynamics simulation

Abstract

The local structure and dynamic behaviour of a benzene molecular assembly confined within the nano-cavities of a zinc-based metal–organic framework, [Zn₄O(CO₂C₆H₄CO₂)₃]_n (IRMOF-1), were investigated by means of molecular dynamics (MD) simulations. The local structure of the confined benzene molecules was evaluated using radial distribution functions. The sites for adsorption of benzene in IRMOF-1 were well defined by the simulation. The diffusion coefficients at ambient temperature suggested that the mobility of the confined benzene was high, comparable to the bulk fluid. Decreasing the temperature gave rise to the aggregation of benzene in the IRMOF-1 frameworks. Molecular aggregation was attributed to the localization of benzene in the large and the small cavities of IRMOF-1, respectively. Both the translational diffusion coefficient and the trajectory of benzene provided evidence that the localization of benzene in the large and the small cavities takes place at ca. 200 K. Furthermore, at high benzene loading, the migration of benzene in the small cavities was prevented (frozen) below 135 K. Thus, the translational degree of freedom of the benzene molecules changed drastically, depending on the temperature.