Electrochemical, spectroscopic, magnetic and structural studies of complexes bearing ferrocenyl ligands of N-(3-hydroxypicolinoyl)picolinamide

Abstract

The synthesis and in-depth characterisation including X-ray crystallography of a new hydroxy derivative of bis(2-pyridylcarbonyl)amine Hbpca, namely N-(3-hydroxypicolinoyl)picolinamide (Hbpca-OH), as well as two ferrocenyl derivatives of Hbpca-OH, namely 2-(picolinoylcarbamoyl)pyridin-3-yl ferrocenoate (HL¹) and bis(2-(picolinoylcarbamoyl)pyridin-3-yl) 1,1′-ferrocenoate (H₂L²), is reported. HL¹ and H₂L² were complexed with five different transition metal cations, namely Fe²⁺, Zn²⁺, Ni²⁺, Cu²⁺ and Cu⁺, to give ten complexes with varying stoichiometries, which were characterised by different analytical methods including ¹H NMR, ESI-MS, IR spectroscopy and microanalysis. The metal complexation was also confirmed by electrochemical measurements for all complexes except Zn(L¹)₂ and FeL², for which the changes in formal redox potentials of ferrocene ΔE°′ observed were not significant enough. Furthermore, two X-ray structures of Cu^II complexes, namely [Cu₂I₂L¹₂] and [Cu₂I₂L²]_n, were determined. Both structures contain an extremely rare Cu^II–I₂–Cu^II bridge. Finally, a small antiferromagnetic coupling in [Cu₂I₂L²]_n was observed.