A family of polyamino phenolic macrocyclic ligands. Acid–base and coordination properties towards Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) ions

Abstract

The acid–base and coordination properties towards Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) of four polyamino-phenol macrocycles 15-hydroxy-3,6,9-triazabicyclo[9.3.1]pentadeca-11,13,1 15-triene L1, 18-hydroxy-3,6,9,12-tetraazabicyclo[12.3.1]octadeca-14,16,1 18-triene L2, 21-hydroxy-3,6,9,12,15-pentaazabicyclo[15.3.1]enaicosa-17,19,1 21-triene L3 and 24-hydroxy-3,6,9,12,15,18-hexaazabicyclo[18.3.1]tetraicosa-20,22,1 24-triene L4 are reported. The protonation and stability constants were determined by means of potentiometric measurements in 0.15 mol dm −3 NMe 4Cl aqueous solution at 298.1 K. L1 forms highly unsaturated Co(II), Cu(II), Zn(II) and Cd(II) mononuclear complexes that are prone to give dimeric dinuclear species with [(MH −1 L1) 2] 2+ stoichiometry, in solution. L2 forms stable Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) mononuclear complexes that can coordinate external species as OH − anion, giving hydroxylated complexes at alkaline pH. L3 forms stable Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) mononuclear complexes and Co(II), Ni(II), Cu(II) and Zn(II) dinuclear [M 2H −1 L3] 3+ species. L4 forms stable mono- and dinuclear Co(II), Cu(II), Zn(II) and Cd(II) complexes, but only mononuclear species with Pb(II). The effect of macrocyclic size is considered in the discussion of results.