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A range of rare earth(III) 4-hydroxybenzoato (4hob) complexes has been prepared by salt metathesis reactions in water and structurally characterized by X-ray single crystal and powder diffraction. Complexes in which 2,2′-bipyridine (bpy) replaces coordinated water were also prepared to compare their anti-corrosion properties, but were largely structurally elusive. [La(4hob)3(H2O)2]n and {[Ce(4hob)3(H2O)2]·3H2O}n were obtained as carboxylate-bridged polymeric sheets, which differ in lattice water, arene ring orientations and the H2O–Ln–OH2 angles, but the bulk powders have the same structure as the La single crystals. The yttrium analogue is a polymeric chain, and [Pr4(4hob)12(H2O)8]·4H2O is a dimer of dinuclear units. Smaller rare earths mainly formed dimeric species, namely [Tb2(4hob)6(H2O)4]·4H2O, [RE2(4hob)6(H2O)4]·2H2O (RE = Eu, Gd, Tb, Dy, Ho, Y, Er, Yb, Lu), and [RE2(4hob)6(H2O)6]·10H2O (RE = Ho, Y, Er). The first two classes differ in having anti–anti and syn–anti carboxylate bridging, and cis and transoid diaqua ligands respectively. The last class not only has an additional water coordinated to each RE atom, but also has a terminal unidentate ligand bonded to each RE atom in place of a chelating 4hob of the first two classes, thereby maintaining eight-coordination. Thus, considerable coordination diversity is observed particularly for RE = Tb, Ho, Y, Er. The bpy complexes, RE(4hob)3(bpy), were largely isolated as amorphous powders and were characterized by elemental analysis and IR spectroscopy. However [RE2(4hob)6(bpy)2]·2bpy·4H2O (RE = Tb, Dy) crystallized as dimers with four bridging (syn–syn) 4hob ligands and one chelating 4hob and one chelating bpy bound to each RE atom. The La, Ce and Y aqua complexes are good corrosion inhibitors for mild steel in 0.01 M NaCl solution with Y > La > Ce in order of effectiveness. Moreover, all aqua 4hob complexes examined outperformed the established inhibitor, cerium(III) salicylate. For RE = La or Y, replacement of coordinated water by bpy improved the anti-corrosion performance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]