Pentadentate thioether-oxime macrocyclic and quasi-macrocyclic complexes of copper(II) and nickel(II)

Abstract

A series of new pentadentate thioether-oximes (TtoxH2, MeTtoxH2, OdtoxH2) were synthesized along with their Ni(II) and Cu(II) complexes. BF2+-bridging is accomplished by reaction of the H-bonded oxime complex with BF3·OEt2, though when Cu(BF4)2 is used as the Cu(II) salt, direct macrocyclization occurs during the metal complexation reaction. Crystallographic studies reveal: [Cu(TtoxH)]ClO4 has a N2S3 square-pyramidal geometry, with an H-bond forming a quasi-macrocycle. In [Cu(OdtoxH)](ClO4)·[Cu(OdtoxH2)](ClO4)2, while retaining the same overall geometry as [Cu(TtoxH)]ClO4, half of the cations are singly deprotonated and the remaining half retain both their protons. In addition, there is an unexpected interaction involving a perchlorate oxygen and the dimethylene bridges between the ligand’s ether oxygen and thioether sulfurs. [Ni(OdtoxBF2)]ClO4·H2O has an N2S2O2 octahedral geometry. The ligand occupies the equatorial plane and one of the apical positions; the coordination sphere is completed by a water oxygen. Cyclic voltammetry and rotating disk electrode (RDE) polarography reveal that N2S3 donor sets stabilize both Ni(III) and Ni(I), whereas the Cu(II) complexes stabilize only Cu(I). The copper complexes show axial ESR spectra typical of tetragonal Cu(II). Nitrogen superhyperfine structure is observed in both the room temperature fluid and 77 K cryogenic glass spectra. Macrocyclization by BF2+ enforces the in-plane geometry around the metal ion.