Alfred Werner revisited: the coordination chemistry of anions.

A series of macrocyclic receptors were designed to probe the influence of four factors, hydrogen bonding, charge, dimensionality, and topology, on anion binding. Monocyclic and bicyclic polyammonium and polyamide receptors were synthesized from either 2,2'-diaminodiethylamine derivatives (dien) or 2,2',2''-aminoethylamine (tren) building blocks, plus aromatic or heterocyclic spacers. Supramolecular complexes of these hosts with three simple anion topologies were probed: spherical (halides), trigonal planar (nitrate), and tetrahedral (sulfate). Results indicate a number of corollaries with transition-metal coordination chemistry in terms of binding concepts such as the chelate effect and dual valencies, as well as geometries for anion complexes that are strikingly similar to those observed in transition-metal coordination chemistry.