SODIUM-ION COMPLEXES WITH ETHYLENEDIAMINETETRAACETIC ACID

The crystal structures of tetrasodium (1,2-ethanediyldinitrilo)tetraac etate pentahydrate and disodium dihydrogen (1,2-ethanediyldinitrilo)te traacetate dihydrate have been determined. Na ions prefer to act as br idges between different edta ligands and only in the tetrasodium salt is the edta ligand hexadentate to one Na ion. Na ions display seven-co ordination, when coordinated to one edta ligand (distorted pentagonal bipyramid), and six-coordination, when linked to several edta ligands (from distorted octahedral to trapezoidal bipyramidal geometry). An Na ion in the tetrasodium salt shows five-coordination, because the sixt h site is blocked by the edta ligand. H atoms in the disodium salt are linked to amine groups. Only these two salts can be obtained on varyi ng the pH of an aqueous solution containing Na+ and ethylenediaminetet raacetic acid. The first is obtained around pH 2-5 and the second arou nd pH 12.