Structure of Mn–EDTA2– complex in aqueous solution by relaxation nuclear magnetic resonance

Abstract

A comprehensive analysis is given for water proton relaxation rates, T^–1₁. and T^–1₂, measured in solutions of Mn–EDTA^2–. Protons of water molecules hydrogen-bonded to co-ordinating carboxylate oxygen atoms of EDTA make a significant contribution to overall relaxation rates. After allowing for these secondary solvation-shell contributions, it is demonstrated that one water molecule is directly co-ordinated to the metal ion. The rotational correlation time of Mn²⁺ ions is increased from 4.2 × 10^–11 to 6.3 × 10^–11 s upon complexation and the electron spin relaxation time decreases from 1.5 × 10^–8 to 1.67 × 10^–9 s at 60 MHz.