Bonding interactions in EDTA complexes

The structural and bonding characteristics of the ethylenediaminetetraacetic acid (EDTA) complexes of 12 metal ions (Mg2+, Ca2+, Sr2+, Ba2+, Al3+, Ga3+, Sn2+, Pb2+, Cu2+, Zn2+, Cd2+, Hg2+) were investigated by means of density functional theory computations. The computed molecular geometries were compared to those in the crystal. The ionic vs. covalent contribution in the bonding was assessed by energy partitioning analysis, while the details of the donor-acceptor interactions were determined by natural bond orbital (NBO) analysis.