The complex formed by the reaction of europium III chloride EuCl and ethylenediaminetetraacetic acid EDTA is a chelate complex, where EDTA acts as a hexadentate ligand. In this complex, europium III ion Eu is the central metal ion, and EDTA coordinates to it through its four carboxylate oxygen atoms and two nitrogen atoms from the amine groups.The coordination geometry of this complex is octahedral, with a coordination number of 6. The symmetry of the complex is O_h, which is the point group for an octahedral complex.The coordination number and geometry of the Eu-EDTA complex do not change significantly with pH. However, the speciation of the complex can change with pH. At low pH, the protonated forms of EDTA e.g., HY, HY can predominate, while at high pH, the fully deprotonated form of EDTA Y is more common. The formation of the Eu-EDTA complex is favored at higher pH values, where the fully deprotonated form of EDTA can chelate the metal ion more effectively.