Gas Diffusion in a Porous Organic Cage: Analysis of Dynamic Pore Connectivity Using Molecular Dynamics Simulations

Molecular dynamics simulations were used to investigate the diffusion of six small gas molecules in a crystalline porous organic cage, CC3. A flexible host model was used to simulate transient channel formation, the effects of which are reflected in the calculated diffusion coefficients for the six gases of 5.64 x 10(-8), 5.94 x 10(-9), 2.60 x 10(-9), 9.60 x 10(-9), 2.40 x 10(-9), and 1.83 x 10(-10) m(2) s(-1), respectively, for H-2, N-2, CO2, CH4, Kr, and Xe. By contrast, a larger gas molecule, SF6, was predicted to be unable to diffuse in the pores of this material. We introduce a new method a void space histogram to analyze dynamic pore topologies and to graphically illustrate the structural factors determining guest diffusion.