A comprehensive review of clathrate inclusion compounds is given. Following this orientating survey, a study of the role of hydrogen bonding in clathrate formation is described, the host chosen for structural modification being Dianin's compound, 4-p-hydroxyphenyl-2,2,4-trimethylchroman. Replacement of the hydroxyl function by the mercapto group gives a new host, which is isomorphous with Dianin's compound, and has sextets of thiol molecules linked by hydrogen bonds involving their SH groups, such that the sulphur atoms form a hexagon. On the other hand, replacement of the OH group of Dianin's compound by the NH2 group gives an amine which undergoes spontaneous resolution on recrystallisation, without inclusion of solvent. The wide-ranging inclusion properties of 3-p-(2,2,4-trimethylchroman-4-yl)-phenyl-2-phenyl-4(3H)-quinazolinone have been studied, important classes of guest being cycloalkanes, cyclic ethers, halides and ketones and aromatic molecules. In the case of the methylcyclohexane adduct, two guest molecules reside in each large closed cavity formed in the crystal host lattice. A thia-analogue of this versatile host has also been investigated. A new rationale for the design of clathrate inclusion compounds, whose structures are not directly related/ related to any known host, is described. This approach, based on analogy is distinct from the earlier idea which depends on making judicious modifications to known hosts. Thus a series of hexa-substituted benzenes which incorporate the same symmetry and overall dimensions as the hydrogen-bonded hexameric units found in the clathrates of phenol, hydroquinone and Dianin's compound have been prepared. No less than twelve "hexa-hosts" have been discovered and shown to exhibit a wide range of inclusion behaviour. The crystals of the carbon tetrachloride adduct of hexaphenylthiobenzene are isomorphous with the above hydrogen-bonded hosts' clathrate structures. Furthermore, the substantial selective inclusion behaviour towards mixtures of isomeric hydrocarbon solvents observed for these hosts is of potential commercial interest
