Selective clathration in a cage-type host lattice of cyclophosphazene

Abstract

Tris(naphthalene-2,3-dioxy)cyclotriphosphazene (TNDOCTP) forms a channel-type clathrate with benzene and also a cage-type one with p-xylene. X-Ray analysis of the p-xylene clathrate showed that the cavity size and form were adequate to accommodate para-disubstituted benzenes into the cage lattice. The extracts obtained from the clathrates which crystallized from a mixture of disubstituted benzenes were analysed by gas chromatography in order to examine the selectivity toward guests by the clathration. TNDOCTP selects most preferentially the para-disubstituted benzenes so that it can isolate para, isomers from ortho, meta, and para, mixtures. The guests that can be included in the cage-type cavity are limited to those having a size and shape similar to that of p-xylene. Among para-substituted toluenes, the host does not recognise the difference among methyl, chloro and bromo groups because of their similarities in size and shape. The crystal grown from an equimolar mixture of p-xylene and benzene is a cage-type p-xylene clathrate and includes only p-xylene, which indicates that the cage-type crystal of TNDOCTP is chosen in preference to the channel-type one. The lattice stability of the former might be preferable to the latter.