Synthesis and competitive 7Li NMR studies of two morpholine-based ligands

Abstract 7Li NMR spectroscopy was used to investigation the stability, stoichiometry and thermodynamic information of a Li+ complex with one known, N1-(2-morpholinoethyl)-N1-((pyridine-2-yl)methyl)propane-1,3-diamine (A1) and one new asymmetrical branched amines, N1-(2-morpholinoethyl)-N1-(pyridine-2-yl)methyl)butane-1,4-diamine (A2) in various acetonitrile-nitromethane solutions. Competitive 7Li NMR was used to probe the complexation of these two amines with Co2+, Ni2+, Cu2+ and Li+ ions in the same solvent systems. The stability constants of the resulting complexes were estimated from fitting of the mole ratio information using an equation that relates the observed chemical shifts to the stability constants. There is a reverse relationship between the stability of the complex and the amount of acetonitrile in the solvent mixture. In all the solvent mixtures, the stability of the 1:1 complex were found to change in the order M-A1>M-A2 and Co2+ > Ni2+ > Cu2+ > Li+. Computational investigations on the ligand structures have been carried out.