Synthesis, structure, and corrosion inhibiting properties of phenylacetato-rare earth(III) complexes

A series of phenylacetato (PhAc) rare earth complexes with aqua and 2,2′-bipyridine (bpy) co-ligands have been synthesized by metathesis reactions in water. Structures of the aqua complexes [RE(PhAc)3(H2O)]n (RE = Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho), {[Lu4(PhAc)12(H2O)2]·1.5H2O}n and the bpy derivatives [RE(PhAc)3(bpy)]2 (RE = Y, Nd, Eu, Er) and {[La(PhAc)3(H2O)].½bpy}n have been determined. Powder XRD determined all aqua complexes except RE = Er, Yb, Lu are isotypic linear polymers, with nine coordinate tricapped trigonal prismatic geometry. The lutetium complex is also a linear polymer, but with distinct metal centers, three eight coordinate, and one nine. Except for RE = La and Ce, the bpy analogues are isostructural symmetrical dimers, with nonacoordinate metal centers. The lanthanum complex is a nonacoordinate linear polymer with coordinated water and lattice bpy. Their corrosion inhibitory properties on mild steel, showed the highest efficiency for [Nd(PhAc)3(H2O)]n (55%). The lanthanum species with solvated 2,2′-bipyridine proved a more effective corrosion inhibitor than the aqua version. Where both the aqua and bpy complexes were tested, the former performed better than the latter. These results provide insight into the effect of structure on the corrosion inhibiting properties of rare earth carboxylates.