Calix[4]pyrrole-capped metalloporphyrins as ditopic receptor models for anions.

Strapped calix[4]pyrrole-metalloporphyrin conjugates, potential hosts for anionic guests, have been synthesized and characterized. The condensation unexpectedly resulted in the formation of the two conformational isomers of calix[4]pyrrole-capped porphyrins 6 and 7. The anion binding studies revealed that only isomer 6 showed strong binding with fluoride anion in organic solvent, and neither isomer showed any appreciable binding with Cl-, Br-, and I-. [structure: see text]