Thermal Evolution and Luminescence Properties of Zn-Al-Layered Double Hydroxides Containing Europium(III) Complexes of Ethylenediaminetetraacetate and Nitrilotriacetate

Europium complexes of ethylenediaminetetraacetate (EDTA) and nitrilotriacetate (NTA), [Eu(EDTA)(H2O)(3)](-), and [Eu(NTA)(2)(H2O)](3-), which have similar geometries but different charge densities, have been incorporated in Zn-Al layered double hydroxides (LDHs). The orientation and loading of the guest anions as well as their thermal stability and reorientation behavior are significantly influenced by their charge density. The maximal dimension of the [Eu(EDTA)(H2O)(3)](-) anion is nearly perpendicular to the LDH layers and a reversible reorientation occurs on mild heating. The structural changes that occurred on heating were followed by variable temperature photoluminescence (PL) measurements. The kinetics of the structural transformation of ZnAl-Eu(EDTA) LDH in the temperature range 30-150 degrees C have also been studied. In the case of [Eu(NTA)(2)(H2O)](3-), the anion adopts a flat orientation in the interlayer galleries with its maximum dimension nearly parallel to the metal hydroxyl layers and no reorientation is observed on heating.