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 anti parallel-stacked, self-complementary cyclic dimer 3(2) or 4(2) 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, 3(2).2(benzene) readily loses one of two guest molecules bound in each cavity to give a microporous half-filled adduct 3(2).(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.