Self-assembly and distinct guest-binding behaviors of double helicate Ag2L2 and triple helicate Fe2L3

Abstract

Two novel metallo-organic helicates were synthesized through the self-assembly in acetonitrile solution by C₂-symmetric amine 4,4′-(naphthalene-2,7-diylbis(oxy))dianiline, 2-pyridinecarboxaldehyde, and different metal centers: silver (I) trifluoromethanesulfonate (Ag(OTf)) and iron(II) trifluoromethanesulfonate (Fe(OTf)₂) respectively. The helicate architectures were confirmed to be double-stranded Ag₂L₂ and triple-stranded Fe₂L₃ by ¹H NMR spectroscopy, HRMS technology and XRD structural analysis. Further host-guest interactions between the helicates and a number of guest molecules were investigated through ¹H NMR experiments. The interaction patterns not only depend on the charge or geometric configuration of guests, but especially on the distinct architecture feature of the two helices with identical ligand. The double helicate with crossed ligand arrangement exhibited significant binding with sodium tetraphenylborate (NaBPh₄), primarily attributed to peripheral C-H···π interactions occurring in multi-sites. In contrast, the triple helicate demonstrated notable host-guest interactions with planar 1-hydroxypyrene, mainly arising from single-site C-H···π interactions via complementary arrangement to central groove surrounded by parallel naphthalene groups. Further quantitative binding stoichiometry revealed that all two helicates formed 1:1 host-guest binding with their respective guests.