2-Amidoindole-based anion receptors

Four receptors containing either 2-amidoindole or 7-nitro-2-amidoindole groups have been synthesised and shown to complex oxoanions in DMSO-d6/0.5% water solution. X-ray crystal structure elucidation reveals that receptor 1 complexes dihydrogen phosphate ion pairs in the solid state, which are part of a continuous chain. While this receptor binds dihydrogen phosphate in a 1:1 stoichiometry in solution, compound 4, which contains 7-nitroindole groups, does form 1:2 receptor:dihydrogen phosphate complexes in DMSO-d6/0.5% water.