Tetraazamacrocycle bearing quinoline pendant arms and its complexation properties

A new tetraazamacrocycle containing two 5-chloro-8-hydroxyquinoline side arms, L1, was synthesized. The protonation constants of L1 and the stability constants of its complexes with Cu2+, Zn2+, Cd2+ and Pb2+ were determined by potentiometric or spectrophotometric methods, at 20 °C in methanol:water (5:1, v/v) and ionic strength 0.10 mol dm−3 in tetrabutylammonium nitrate (TBAN). Compound L1 has three high protonation constants, the most basic centres being both phenolates of the arms. Mono- and dinuclear complexes were found in solution for all the metal ions, the complexes of copper are thermodynamically very stable, and the dinuclear complexes of lead(II) are the predominant species even in 1:1 mixtures. UV–Vis spectra of some complexes and EPR of the copper ones confirmed the presence of dinuclear complexes.