Self-assembly and peripheral guest-binding of two triangular Zn(II) helicates

Two Zn(II) complexes, referred to as helicate 1 and helicate 2, were synthesized using subcomponent self-assembly of zinc(II) trifluoromethanesulfonate (Zn(CF₃SO₃)₂), 2,4,6-tris(3-aminophenoxy)triazine, and either 2-formylpyridine or 3-methyl-2-pyridinecarboxaldehyde in CH₃CN solution. The triangular helicate structure of both complexes was verified by ¹H NMR and ESI–MS measurements, and the host–guest interactions between the helicates and a number of guest molecules were investigated. It was discovered that the effect of the host–guest interactions significantly changed when the aldehyde component was replaced by 3-methyl-2-pyridinecarboxaldehyde, which suggested that the guest-binding sites may occur around the peripheral apertures of the complex. Additionally, the binding behaviour between helicate 1 and tetraphenylborate guests was further investigated, which allowed for the quantification of the host–guest stoichiometry in a 1:2 ratio.