Copper(II) and nickel(II) complexes of mono-oxocyclam(5-oxo-1,4,8,11-tetraazacyclotetradecane). Synthetic and potentiometric studies

Abstract

The macrocyclic mono-oxotetraamine, 5-oxo-1,4,8,11-tetraazacyclotetradecane (mono-oxocyclam=LH) has been prepared by reaction of methyl acrylate with 2,3,2-tetra(1,9-diamino-3,7-diazanonane). The protonation constants of the ligand are log K1=9.40, log K2=6.65 and log K3=2.87 at 25 °C (I=0.1 mol dm−3 NaClO4). Detailed potentiometric studies of the interaction of the base with copper(II) and nickel(II) have been carried out. In the pH range 2.5–7.0 two complexes, [CuLH]2+ and [CuL]+, form; the deprotonated complex being 100% abundant at pH 7. For nickel(II), only [NiL]+ forms (log β11−1 = 3.90), the yellow low spin nickel complex reaching its maximum concentration above pH 6. The [CuL][ClO4] · H2O and [NiL][ClO4] 0.5 H2O complexes have been characterised in the solid state. The nickel(II) complex is square planar with a d-d band at 22625 cm−1.