A solution thermodynamic study of the Cu(II) and Zn(II) complexes of EBTA: X-ray crystal structure of the dimeric complex [Cu2(EBTA)(H2O)3]2

Abstract The copper(II) complex of the acyclic EBTA ligand (H 4 EBTA = 1,2-bis(2-aminoethoxy)benzene- N , N , N ′, N ′-tetraacetic acid) has been prepared and characterized by X-ray analysis. The two copper ions of the dinuclear unit present the same distorted octahedral coordination polyhedra. The EBTA ligand is shared between two copper coordination centres, with the formation of centrosymmetric dimers, which are linked in a supramolecular tridimensional structure via additional interactions through the coordinated waters molecules with adjacent carboxylic oxygen atoms. The stability and protonation constants of EBTA with Cu(II) and Zn(II) ions indicate a higher stability of these complexes with respect to the corresponding complexes with the more flexible EGTA ligand (H 4 EGTA = ethyleneglycol-bis(2-aminoethylether)- N , N , N ′, N ′-tetraacetic acid). On the other hand, the lower stability of [Gd(EBTA)] − than [Gd(EGTA)] − results in a decreased overall selectivity (lower K sel ) of EBTA towards Gd(III) and suggests that this complex may undergoes transmetallation reactions under physiological conditions.