Competitive 7Li NMR study of the stoichiometry, stability and thermodynamic data for the complexation of Li+, Mn2+, Zn2+ and Cd2+ ions with two asymmetrical branched pentadentate (N5) amines containing pyridine moiety in ionic liquid–acetonitrile mixtures

• Using 7 Li NMR spectroscopy to investigate the stoichiometry of Li + complex of amines • The formation constants of the resulting complexes were evaluated from computer fitting. • The inverse relationship between the complex stability and the amount of ionic liquid. Lithium-7 NMR spectroscopy was used to investigate the stoichiometry, stability and thermodynamic data of a Li + complex with two asymmetrical branched amines, 3,6-bis(2-pyridylmethyl)-5-methyl-3,6-diazahexane-1-amine (A 1 ) and 4,7-bis(2-pyridylmethyl)-6-methyl-4,7-diazaheptane-1-amine (A 2 ) in 50–50 and 75–25 wt% acetonitrile (AN)- [BMIM][PF 6 ] (ionic liquid) mixture solution at various temperatures. A competitive 7 Li NMR method was also employed to probe the complexation of Mn 2+ , Zn 2+ and Cd 2+ ions with A 1 and A 2 in the same solvent systems. 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. There is an inverse relationship between the complex stability and the amount of ionic liquid in the solvent mixtures. The temperature dependence formation constant was used for the evaluation of the enthalpy and entropy values for the complexation reaction. It was concluded that in all complexes, except for lithium ion, the resulting complex enthalpy is stabilized and the Δ H compensates the T Δ S contribution. In the all studied solvent mixtures, the stability of the resulting 1:1 complexes was found to vary in the order Cd 2+ > Mn 2+ > Zn 2+ > Li + .