Competitive 7Li NMR study of the stoichiometry and stability of Mn2+, Zn2+ and Cd2+ complexes with three new branched hexadentate (N6) amines containing pyridine moiety in acetonitrile-[BMIM][PF6] mixture solutions

Three new branched hexadentate amines, N1, N1 - (1, 2 - phenylene) bis (N1 - (pyridine - 2 -ylmethyl) ethane- 1, 2 - diamine) (A1), N1, N1 - (1, 3 - phenylene) bis (N1 - (pyridine - 2 -ylmethyl) ethane - 1, 2 - diamine) (A2) and N1, N1 - (1, 4 - phenylene) bis (N1 - (pyridine - 2 -ylmethyl) ethane - 1, 2 - diamine) (A3), have been synthesized (Scheme 1). Lithium-7 NMR spectroscopy was used to investigate the stoichiometry and stability of a Li+ complex with A1, A2 and A3 amines, in 100-0%, 75-25%, 50-50 and 25-75 wt% acetonitrile (AN)- [BMIM][PF6] (ionic liquid) mixture solution at 25℃. A competitive 7Li NMR method was also employed to probe the complexation of Mn2+, Zn2+ and Cd2+ ions with A1, A2 and A3 in the same solvent system [1]. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant [2]. In all solvents, the stability of the resulting 1:1 complexes was found to vary in the order Cd2+ Zn2+ Mn2+ Li+. The resulting complexes with the amines A1, A2 and A3 vary in the order of MA1 MA2¬ MA3.