1,3-diindolylureas and 1,3-diindolylthioureas: anion complexation studies in solution and the solid state.

1,3-Diindolylureas and thioureas have been synthesised and their anion complexation properties in solution studied. Whilst diindolylthioureas showed only moderate affinities and selectivities, diindolylureas show remarkably high affinity for dihydrogen phosphate in solution for an acyclic, neutral receptor in water/[D(6)]DMSO mixtures. These easy-to-make compounds adopt relatively planar conformations in the solid-state and are able to donate four hydrogen bonds and yet not fill the coordination sphere of carbonate or phosphate, allowing two or three receptors to bind to each anion in the solid-state.