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–1 1. and T–1 2, measured in solutions of Mn–EDTA2–. 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.

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