Intracrystalline diffusivities and surface permeabilities deduced from transient concentration profiles:: Methanol in MOF manganese formate

The intracrystalline concentration profiles during molecular uptake of methanol by an initially empty, single crystal of microporous manganese(II) formate (Mn(HCO2)(2)), representing an ionic inorganic-organic hybrid within the MOF family, are monitored by interference microscopy. Within these profiles, a crystal section could be detected where over the total of its extension (approximate to 2 mu m x 50 mu m x 30 mu m) molecular uptake ideally followed the pattern of one-dimensional diffusion. Analysis of the evolution of intracrystalline concentration in this section directly yields the permeability of the crystal surface and the intracrystalline diffusivity as a function of the concentration of the total range of 0 <= theta <= 0.57 covered in the experiments. Within this range, the surface permeability is found to increase by 1 order of magnitude, while, within the limits of accuracy (+/- 30%), the transport diffusivity remains constant, thus reflecting the properties of the lattice gas model.