Bis-amidopyrrolyl Receptors Based on Anthracene and Carbazole

A new set of diamide receptors containing anthracene and carbazole bridging subunits and either pyrrole or phenyl substituents were synthesized. The four systems produced in this way were shown to bind representative anions in DMSO-d(6) solution and in the solid state. A higher relative affinity for two test oxoanions, namely dihydrogen phosphate and benzoate, over chloride anion was seen in solution, with the anions in question being studied in the form of their respective tetrabutylammonium salts. However, the specifics of the anion recognition process were seen to depend on structure, with the pyrrole-containing systems displaying higher relative affinities than their corresponding phenyl-containing congeners, and the carbazole receptors proving more effective than the anthracene analogues. Such observations provide support for the notion that both the carbazole NH and the pyrrolic NH protons play an important role in stabilizing the receptor-bound anions in solution. Structural analyses of several anion complexes of the diamidopyrrole carbazole receptor reveal that this is not necessarily the case in the solid state; specifically, the pyrrole NH protons are seen to interact with the amide oxygen of another molecule. The net result is an extended a one-dimensional coordinaton polymer.