The macro properties of crystalline inclusion compounds depend on their structures. Their thermal stabilities are a function of the strength and the directionality of the various nonbonded interactions occurring in the host-guest assembly. Their lattice energies, as measured by the method of atom-atom potentials, correlate with the thermodynamics of the guest-release reactions and the selectivity that a given host displays for a particular guest. The kinetics of solid-host:vapor-guest reactions and of guest exchange are important in our understanding of catalytic processes. Crystal engineering, in which materials of predetermined properties may be synthesized, is still at the empirical stage.

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1,1,6,6-Tetraphenylhexa-2,4-diyne-1,6-diol (H) forms inclusion compounds with 2-, 3-, and 4-aminobenzonitrile (2ABN, 3ABN, and 4ABN). In each case the host:guest ratio is 1:2 and the structures are stabilized by hydrogen bonds. Competition experiments show that the host selects the guests in order of preference of 2ABN > 3ABN > 4ABN. These results are in general agreement with lattice energy calculations, thermal analyses, and solid-state reactions. The structure of the solid formed between H and a mixture of 3ABN and 4ABN has also been elucidated.

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Two similar fluorenyl diol hosts H1 and H2 have been employed to study their selectivity toward methylated piperidines. Crystal structures show strong similarities in the packing of these inclusion compounds, but the interesting result arises from the competition of these hosts for equimolar dimethylpiperidines (2,6DMP and 3,5DMP). H1 selects 3,5DMP, while H2 selects 2,6DMP. Packing analysis and lattice energy calculations failed to explain this result, but the differential scanning calorimetry profiles of the four host−guest compounds are in agreement with the selectivity experiments.

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