Spectrophotometric and potentiometric study on iron(II) complexes with some macrocyclic ligands

One new macrocycle, 4,10-bis(2-hydroxy-5-nitrobenzyl)-4,10-diaza-1,7,-dioxadodecane (L0) has been synthesised and characterised. Its basicity behaviour, as well as that of the two related azamacrocycles 1,7-bis(2-hydroxy-5-nitrobenzyl)-4,10-dimethyl-1,4,7,10-tetraazadodecane (L1) and 1,13-bis(2-hydroxy-5-nitrobenzyl)-4,10-dimethyl-4,7,10,16-tetramethyl-1,4,7,10,13,16-hexaazaoctadecane (L2), was studied by potentiometry in 0.1 M N(CH3)4Cl at 25 °C, characterising moreover the ionisation processes related to macrocyclic nitrogens and to nitrophenolic moieties on the base of spectral variations. The equilibria of the three ligands with iron(II) were studied. 1:1 complexation models with different protonation degrees were found for the three ligands and the related formation constants were estimated from potentiometric results. The pH distribution curves are discussed on the basis of spectrophotometric findings.