Crystalline Host-Guest Complexes of Constitutionally Isomeric Diol Hosts. A Structural Case Study

The formation of crystalline host-guest complexes of three constitutionally isomeric host compounds 1-3 featuring two diphenylhydroxymethyl groups attached in different positions to a biphenylylene central moiety is studied. Dependent on the connection mode (2,2'-, 3,3'-, or 4,4'-) with reference to the biphenylylene unit, a distinctly different complex behavior of the host compounds is observed. X-ray crystal structures of the solvent-free hosts are reported including a third polymorph with respect to already known polymorphous structures. The crystal structures of eight host-guest complexes of 1-3, including a pair of complexes differing only in the host/guest stoichiometry, are described and comparatively discussed covering the structures of known complex species of the isomeric hosts. Correlations between the constitutional isomerism of the host molecules and their conformational as well as packing structures in the crystalline state, both in unsolvated and solvent complexed form, are demonstrated providing potential usefulness in the future design of crystalline host-guest complexes.