Density functional complexation study of metal ions with amino polycarboxylic acid ligands: EDDHA and HBED in comparison to EDTA, EDDS, ODS, and ISA

Metal complexes of amino polycarboxylic acid ligands have been studied using density functional methods and a continuum solvation model (COSMO). Complexation energies for complexes of Mg²⁺, Ca²⁺, Mn²⁺, Fe³⁺, and Zn²⁺ have been determined. The studied ligands include ethylenediaminedi-(o-hydroxyphenylacetic)acid (EDDHA) (including its ortho,ortho, ortho,para, and para,para-isomers), N,N′-bis(2-hydroxybenzyl)ethylenediamine-N,N′-diacetic acid (HBED), ethylenediamine tetraacetic acid (EDTA), ethylenediiminodibutanedioic acid (EDDS), meso-oxybis(butanedioic acid) (ODS), and 2,2′-bis(carboxymethyl)iminodiacetic acid (ISA). New, more accurate parameterisation is introduced to correct the neglected contributions in energetics. For o,o-EDDHA, the method is tested also for partly deprotonated forms of ligand. The results indicate that o,o-EDDHA^4- and HBED^4- are clearly the most effective ligands for all the metals.