Zinc-mediated diastereoselective assembly of a trinuclear circular helicate

Abstract

Coordination of a triptycene-based ditopic Schiff base ligand (H₂L) with Zn²⁺ leads to the formation of a novel trinuclear circular species. A combination of ¹H NMR spectroscopy, infrared spectroscopy, mass spectrometry and elemental analysis allow the unambiguous characterization of H₂L and Zn₃L₃·8H₂O. DFT molecular modelling has been used to study the possible isomers of the cyclic trinuclear Zn(II) complex that results from the combination of conformational and optical isomers of the ligand. A NOESY experiment demonstrated that in the trinuclear circular zinc(II) helicate the three isomers of the ligand have an anti configuration of N,O-donor domains and an s-cis configuration of their imine bonds. Besides, a UV-VIS absorption and fluorescence emission study of H₂L and Zn₃L₃·8H₂O has been performed.