Tuning the anion binding properties of calixpyrroles by means of p-nitrophenyl substituents at their meso-positions

Extended cavity calix4]pyrroles and a calix6]pyrrole were synthesized by cyclization of 5-methyl-5-(4-nitrophenyl)dipyrromethane with acetone in the presence of acid. The solid-state structures of the novel macrocycles were determined by X-ray crystallography. The host-guest chemistry of these receptors towards halide ions was investigated in solution by ¹H NMR titration techniques and compared with those of the meso-octamethylcalix4]pyrrole and meso-dodecamethylcalix6]pyrrole. The binding of chloride anions was observed to occur with different affinities on the two faces of the novel calix6]pyrrole derivative described here.