Competitive 7Li NMR study of the stoichiometry and stability for the complexation of 〖UO〗_2^(2+) ion with two new amines containing pyridine moiety in acetonitrile–methanol mixtures

Lithium-7 NMR spectroscopy was used to investigate the stoichiometry and stability of a Li+ complex with two asymmetrical branched amines, 3,6-bis(2-pyridylmethyl)-5-methyl-3,6-diazahexane-1-amine (A1) and 4,7-bis(2-pyridylmethyl)-6-methyl-4,7-diazaheptane-1-amine (A2) in acetonitrile (AN) – methanol (Me) mixture solutions [1]. A competitive 7Li NMR method was also employed to probe the complexation of 〖UO〗_2^(2+) ion with A1 and A2 in the same solvent systems (Scheme 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. There is an inverse relationship between the complex stability and the amount of Methanol in the solvent mixtures. In the all studied solvent mixtures, the stability of the resulting 1:1 complexes was found to vary in the order 〖UO〗_2^(2+)-A^1 〖UO〗_2^(2+)-A^1. It was found that, in the case of all complexes, an increase in the percentage of Methanol in the solvent mixtures would significantly decrease the stability of the complexes.