Acridinylresorcinol as a Self-Complementary Building Block of Robust Hydrogen-Bonded 2D Nets with Coordinative Saturation. Preservation of Crystal Structures upon Guest Alteration, Guest Removal, and Host Modification

Acridinylresorcinol host 3 (9-(3,5-dihydroxy-1-phenyl)acridine) forms such adducts as 3·(benzene),
3·(chloroform), 3·0.5(toluene), and 3·(isobutyl benzoate). Modified acridinol host 4 (9-(3,5-dihydroxy-1-phenyl)-4-hydroxyacridine) having an additional OH group on the acridine ring affords such adducts as
4·(benzene), 4·(chloroform), 4·0.5(toluene)·0.5(water), 4·(methanol)·(water), and 4·(ethyl acetate). In the
crystals, hosts 3 and 4 form hydrogen-bonded (O−H···O−H) poly(resorcinol) chains which are linked
together via interchain O−H···N hydrogen bonds to give a coordinatively saturated (O−H···O−H···N) 2D
net composed of doubly hydrogen-bonded and antiparallel-stacked, self-complementary cyclic dimer 32 or
42 as a rigidified building block, the otherwise flexible O−H···O−H hydrogen bonds being thereby taken in
a cyclophane-like structure. This network turns out to be remarkably well preserved among the above
adducts. Guest molecules, which are disordered in many cases, are incorporated in the cavities left. The
binding of small polar guests to host 4 is primarily due to hydrogen bonding to the OH group on the acridine
ring. The latter therefore acts only as a polarity modifier of preserved cavities. Adduct 3·(benzene), that is,
32·2(benzene) readily loses one of two guest molecules bound in each cavity to give a microporous half-filled adduct 32·(benzene) which adsorbs 1 mol of benzene to regenerate the starting full adduct without
involving a phase change, as confirmed by X-ray powder diffractions and reversible Langmuir-type
adsorption/desorption isotherms. The self-complementarity strategy for designing rigid crystal structures is
discussed with a particular reference to the possibility of systematic perturbation/variation approaches in
crystal engineering.