Understanding stable adsorption states in flexible soft porous coordination polymers through free energy profiles†

Abstract

Soft porous coordination polymers (SPCPs) are flexible porous materials comprised of metal–organic polyhedrons (MOPs) connected by organic linkers, with potential in adsorption applications. We performed molecular simulations of various SPCPs that vary in the length and flexibility of the organic linkers to address how the flexibility can result in various configurations and affects adsorption performance. We examined free energy profiles as a function of volume of different SPCPs while varying methane loading, resulting in different stable configurations. We found significant differences in the volume of the stable configurations and their number for the various structures, with more flexible linkers having more stable configurations in free energy. We also characterized the textural properties and methane adsorption isotherms of the stable configurations for the SPCPs and analyzed density profiles of the adsorption in the various configurations. Altogether, our examination can be used to predict the relevant configurations of the SPCPs at a given loading and provides molecular-level understanding of how the flexibility of the organic linkers affects the structure of the system and adsorption performance.