Synthesis, and characterization of cobalt(III) complexes with Schiff bases derived from 2-hydroxynaphthaldehyde, (naph)2dien and (naph)2dpt, and monodentate amine ligands: Crystal structure, spectral and redox properties

Two series of complexes of the type [CoIII{(naph)2dien}(amine)]BPh4 {(naph)2dien = bis-(2-hydroxy-1-naphthaldimine)-N-diethylenetriamine dianion, and amine = piperidine (pprdn) (1), pyrrolidine (prldn) (2), pyridine (py) (3), N-methylimidazole (N-MeIm) (4)}, and [CoIII{(naph)2dpt}(amine)]BPh4 {(naph)2dpt = bis-(2-hydroxy-1-naphthaldimine)-N-dipropylenetriamine dianion, and amine = piperidine (pprdn) (5), 3-methylpyridine (3-Mepy) (6)} have been synthesized and characterized by elemental analyses, IR, UV–Vis, and 1H NMR spectroscopy. The crystal structures of (2) and (6) have been determined by X-ray diffraction. The redox potentials of the central cobalt ion show a relatively good correlation with the σ-donor ability of the axial ligands. The spectroscopic and electrochemical properties of these complexes are also influenced by the mutual steric hindrance between the pentadentate Schiff base and the ancillary ligands.

The synthesis and structures of [CoIII{(naph)2dien}(amine)]BPh4 and [CoIII{(naph)2dpt}(amine)]BPh4 complexes are reported. The effect of the ancillary ligands, mutual steric hindrance between pentadentate Schiff base and the bulky ancillary ligands, and the influence of the fused phenyl rings of (naph)2dien and (naph)2dpt on the spectroscopic and redox properties of cobalt complexes are presented.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis of Schiff bases L = (naph)2dien, (naph)2dpt, and [CoIII(L)(amine)]BPh4.
► Investigation of the structure, spectroscopic, and electrochemical properties.
► X-ray structures of [CoIII{(naph)2dien}(prldn)]+ and [CoIII{(naph)2dpt}(3-Mepy)]+.
► The steric and electronic effects of the ligands on Co(III)/Co(II) redox potential.
► The CoIII/II reduction occurs at more positive potentials relative to Me-sal analogs.