Influence of Different Ligand Isomers on the Growth of Lanthanide Phosphate Nanoparticles

Abstract

The steric position of the methoxy group in different isomers of methoxycinnamic acid ligands is observed to have a strong impact on the particle growth of lanthanide phosphate nanoparticles. Very small nanoparticles with a mean size of less than 4 nm are obtained for all phosphates from lanthanum to europium, if 3-methoxycinnamic acid or trans-4-methoxycinnamic acid are used as ligands or if these methoxy isomers are replaced by cinnamic acid or phenylpropionic acid. However, if trans-2-methoxycinnamic acid is employed in the synthesis, anisotropic particle growth along the [200] axis is observed, yielding elongated nanoparticles with an average length of up to 25 nm. Our results indicate that in all cases small nanoparticles are formed first at early stages of the synthesis and that these particles grow to larger particles only if trans-2-methoxycinnamic acid is used as the ligand. We assume that the position of the methoxy group in trans-2-methoxycinnamic acid leads to an easier displacement or removal of these ligands from the surface of the small particles, resulting in a less effective shielding of the particles against particle growth.