Probing host-guest interaction energies in solid inclusion compounds from experimental studies of competitive inclusion

An approach to assess host-guest interaction energies in solid inclusion co mpounds with tunnel host structures is described, based on experimental stu dies of competitive inclusion of two different types of potential guest mol ecules X(S)(q)X and X(S)(r)X (q not equal r) within the host tunnel. The pr oportions (m and 1-m) of the two types of guest molecule included within th e host tunnel depend on the proportions (gamma and 1-gamma) of the two type s of guest in the external "pool" of potential guest molecules and the rela tive "affinities" (chi and 1/chi) of the host tunnel for including the two types of guest. Expressions linking chi, m and gamma can be applied to dete rmine chi directly From experimental measurements of m for inclusion compou nds prepared with different values of gamma, The value of chi depends on th e intermolecular interaction energies per unit length of tunnel for the two types of guest molecule, and chi may be expressed in terms of the host-gue st interaction energies for the spacer units S and the end-groups X, and th e guest-guest (X . . .X) interaction energy. Preliminary experimental resul ts for urea inclusion compounds containing binary mixtures of alpha,omega - dibromoalkane guest molecules are presented.