Clathrates with halogens

The skeletal nitrogen atoms in cyclophosphazenes possess a lone pair of electrons and, hence, they have long been viewed as potential donor sites to bind a proton or to form complexes with electron-acceptor molecules. The possibility of formation of anion-cation complexes by release of a halogen ion to a Lewis acid and charge-transfer complexes has also been studied. In addition, some cyclopho-sphazene derivatives form crystalline inclusion clathrates with a variety of guest molecules. Allcock (21, 22) has reviewed these aspects in detail. 

The range of compounds which combine with thiourea is still more varied. As regards their formation, the rule is that clathrates are most easily formed from aliphatic compounds with two methyl groups or with substituents of approximately the same size (halogens) in the chain. A larger side chain (ethyl, isopropyl) prevents the formation of clathrates with thiourea. Thiourea also forms adducts with cycloparaffins simple aromatic compounds (benzene, nahphthalene, anthracene) do not form clathrates with thiourea. 

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