Probing Host-Guest Interaction Energies in Solid Inclusion Compounds from Experimental Studies of Competitive Inclusion

Abstract

An approach to assess host-guest interaction energies in solid inclusion compounds with tunnel host structures is described, based on experimental studies of competitive inclusion of two different types of potential guest molecules X(S) q X and X(S) r X (q ≠ r) within the host tunnel. The proportions (m and 1-m) of the two types of guest molecule included within the host tunnel depend on the proportions (γ and 1-γ) of the two types of guest in the external “pool” of potential guest molecules and the relative “affinities” (χ and 1/χ) of the host tunnel for including the two types of guest. Expressions linking χ, m and γ can be applied to determine χ directly from experimental measurements of m for inclusion compounds prepared with different values of γ. The value of χ depends on the intermolecular interaction energies per unit length of tunnel for the two types of guest molecule, and χ may be expressed in terms of the host-guest interaction energies for the spacer units S and the end-groups X, and the guest-guest (X…X) interaction energy. Preliminary experimental results for urea inclusion compounds containing binary mixtures of α,Ω-dibromoalkane guest molecules are presented.