Macrocyclic complexes: Part XIII - syntheses, structure & electrochemical properties of Co (III) -Ph4 cyclopean complexes

Abstract

Cobalt(III) complexes of the types, [Co(Ph₄cyclopean)YX]⁺,[Co(Ph₄cyclopean)X]⁺ and [Co(Ph₄cyclopean)]⁺, [Y = pyridine, <em>β</em>-picoline or γ-picoline and X = Cl^-, Br^-, or I^-] have been synthesised from the respective cobalt(III) oximato open chain precursors by cyclization with BF₃. The IR spectral data indicate that the nitrogen atoms of the cyclic ligands and their precursors are coordinated to the metal ion. The electronic spectra of the [13]-, [14]- and [16]-membered cyclopeans show low symmetry ligand field components corresponding to tetragonal symmetry while the spectra of the [19]-membered cyclopean complexes conform to an octahedral geometry. Each cobalt(III) complex shows two one-electron redox waves. The redox steps for macrocyclic complexes of the type [Co.cyclop.YX]⁺ occur at relatively more anodic potentials than those for the corresponding precursors, but the redox steps of the sixteen- and nineteen-membered cyclic complexes are more cathodic than those of their respective open chain counterparts.