A host material may be used for the separation of elements or compounds, wherein the host material is an organic molecular solid with suitable cavities for accommodating a guest material to be separated, and with interconnections between the cavities to allow the guest material to diffuse through the host material, and wherein said interconnections are closed for a proportion of the time or have a static pore limiting diameter which is smaller than the static dimension of the guest material. Applications include separations of rare gases, chiral molecules, and alkanes. One class of suitable host materials may be made by imine condensation.

A host material may be used for the separation of elements or compounds, wherein the host material is an organic molecular solid with suitable cavities for accommodating a guest material to be separated, and with interconnections between the cavities to allow the guest material to diffuse through the host material, and wherein said interconnections are closed for a proportion of the time or have a static pore limiting diameter which is smaller than the static dimension of the guest material. Applications include separations of rare gases, chiral molecules, and alkanes. One class of suitable host materials may be made by imine condensation.