Synthesis of acyclic tetrakis- and pentakis(N₂O₂) ligands for single-helical heterometallic complexes with a greater number of winding turns

Abstract

Acyclic oligooxime ligands (H8L4 and H10L5) that have four or five N2O2 coordinating moieties (salamo moieties) were synthesised in order to obtain single-helical metal complexes with a greater number of winding turns. When the complexation of the tetrakis (salamo) ligand H8L4 with zinc(II) took place, a complicated mixture of zinc(II) complexes was formed. However, the mixture was converted to a discrete pentanuclear complex in the presence of a guest ion with a suitable size (La3+, Ba2+), which was evidenced by the well-resolved sharp 1H NMR spectra and the mass spectra. Other ions with a smaller size (Lu3+, Ca2+) did not lead to such a discrete species. The 1H NMR spectral feature of the pentanuclear complex [L4Zn4La(OAc)3] is consistent with the single-helical structure in which the nth benzene ring approximately lies on the (n+3)th benzene ring.