Competitive 7Li NMR Study on the Mn2+, Zn2+ and Cd2+ Complexes of Two New Branched Hexadentate (N6) Amines Containing the Pyridine Moiety in Nitromethane and Acetonitrile Solutions

Lithium-7 NMR spectroscopy was used to investigate the stoichiometry and stability of a Li+ complex with two new branched amines, 4,7-bis(2-pyridylmethyl)-4,7-diazadecane-1,10-diamine (L-1) and 4,8-bis(2-pyridylmethyl)-4,8-diazaundecane-1,11-diamine (L-2), in acetonitrile and nitromethane. A competitive Li-7 NMR method was also employed to probe the complexation of Mn2+, Zn2+ and Cd2+ ions with L-1 and L-2 in the same solvent systems. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data with an equation that relates the observed chemical shifts to the formation constant. In both solvents, the stability of the resulting 1:1 complexes was found to vary in the order Cd2+ > Zn2+ > Mn2+ > Li+.