The determination of pore volumes, pore shapes and diffusion paths in microporous crystals

Abstract

The original optionSOLVof the programPLATON, which is primarily devoted to the study of organic structures, has been extended to studies of microporous inorganic crystals. The space that is available for a potential spherical guest within a pore can be regarded as being outlined by rolling a sphere of the guest's radius over the surfaces of the host atoms that form the pore. The volumes of the pores are determined in Å3and the pore shapes can be drawn. The pore volumes of several microporous phases have been calculated and compared with results obtained with other methods. An essential feature of the program is the option to vary a parameter called `probe radius', which models the size of a guest. The decision whether a void is a pore or not and the dimensionality of a pore depend on the radius of the guest, which is approximated by a sphere. This is demonstrated for the structure of the zeolite afghanite. With decreasing probe radius, cages can coalesce into larger cages and finally into channels and channel systems. The variation of the probe radius allows one to determine whether a window between adjacent pores is permeable to guests; in addition, diffusion paths in zeolites and zeolite-like structures can be determined and visualized.