WHAT MAKES CLATHRATES STABLE? Kersti Hermansson, Dept. of Chemistry, Uppsala University, Box 531, S-75121 Uppsala, Sweden

The [[beta]]-quinol clathrate crystal is built up of approximately spherical cages, about 4 Å in diameter. This cage structure is stable only when guest molecules are trapped within the cages. Without guests, another modification of quinol, the [[alpha]]-form, is the most stable structure. The experimentally measured enthalphy difference for the process [[alpha]]-quinol --> [[beta]]-quinol is only 0.6 kJ/mol. The enthalphy change for the inclusion of guest molecules into the [[beta]]-quinol cages has been measured to -25 to -60 kJ/mol, depending on the type of guest molecule.

Many experimental studies of [[beta]]-quinol inclusion compounds have been reported. The preferred sites and the motion of the guest molecules in the cages have been investigated. No ab initio calculations of these crystalline compounds have yet been presented.

This paper presents results from crystal-orbital calculations of different [[beta]]-quinol inclusion compounds at the Hartree-Fock and Hartree-Fock + DFT levels. Optimized structures, clathrate formation energies and the much debated role of the guest-guest interactions will be presented.