On a mechanism of low-pressure insertion of chain molecules into crystalline matrices

A microscopic mechanism of low-pressure insertion and separation of chain-like molecules in host matrices is proposed. It is shown that the intramolecular correlations combined to appropriate host activities are responsible for a low-pressure condensation of chain molecules. This allows to recover a fine structure of the isotherms and to explain recent experiments on the insertion of C(2)H(2) and CO(2) guest species into metal-organic microporous materials. We argue that the mechanism should be dominant in low-dimensional host geometries, where the effects related to the chain conformations or reorientations are strongly suppressed and the major factors are the chain connectivity and the segment packing.