Anion control of the formation of geometric isomers in a triple helical array

The amide-substituted unsymmetrical ligand L1 upon coordination to Co2+ forms the dinuclear triple helicate [Co2(L1)3]4+ which exists as both possible C1 and C3 symmetric geometric isomers in solution, however, upon addition of nitrate ions, the formation of an anion binding cavity is favoured and hence the sole product is the C3 symmetric isomer in which all three amide substituents are hydrogen bonded to the nitrate anion.