Nuclear magnetic resonance study of the stoichiometry and stability of two new 〖UO〗_2^(2+) hexadendentate amines complexes in various acetonitrile-methanol mixtures

Competitive NMR technique using 7Li nucleus as a proe were employed to monitor the stability of 〖UO〗_2^(2+) ion complexes with Two new branched hexadentate amines, 4,8 – bis (2-pyridylmethyl) - 4,8 - diazaundecane - 1,11 - diamine (A1) and 4,9-bis(2-pyridylmethyl)-4,9-diazadodecane - 1,12 - diamine (A2) in binary acetonitrile – Methanol mixtures of varying composition [1,2]. In all cases, the variation of 7Li chemical shift with [L]/[ 7Li] mole ratios indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation which relates the observed chemical shifts to the formation constants. It was found that, in pure acetonitrile, the stabilities of the resulting 1:1 complexes vary in the order A^1 A^2. The observed changes in the stability order could be related to the specific interactions between Amines and acetonitrile. It was found that, in the case of all complexes, an increase in the percentage of Methanole in the solvent mixtures would significantly decrease the stability of the complexes.