Rare‐Earth 4‐Hydroxyphenylacetate Complexes: Synthesis, Structural Characterization, and Corrosion Inhibition Properties

Four structural types of rare‐earth aqua 4‐hydroxyphenylacetate complexes {[Ce(L) 3 (H 2 O) 2 ]·H 2 O} n ( a ), {[RE 2 (L) 6 (H 2 O)]·4H 2 O]} n (RE = Nd ( b ), Gd ( c )), {[RE 2 (L) 6 (H 2 O)]·3H 2 O]} n (RE = Dy ( d ), Y ( e )), {[RE 2 (L) 6 (H 2 O)]·5H 2 O]} n (RE = Er ( f ), Yb ( g )), (L = 4‐hydroxyphenylacetate) have been synthesized by salt metathesis reactions of corresponding rare‐earth metal chlorides or nitrates and sodium 4‐hydroxyphenylacetate (NaL) in a water/ethanol solvent system. The compounds are targeted for structural interest and to determine if the 4‐hydroxy (4‐OH) substituent would enhance the anti‐corrosion properties of rare‐earth phenylacetates. Single crystal X‐ray diffraction (XRD) determined the crystal structures of all compounds except the complex of Gd ( c ), which was shown to be isomorphous with the Nd complex ( b ) by the powder XRD pattern. All compounds were obtained as one‐dimensional polymeric structures. The structure of a differs in being a monometallic repeating unit and having two coordinated waters whilst the others have binuclear repeating units that resulted from the alternating coordination of one water molecule along the chain. Weight loss and potentiodynamic polarization tests reveal that {[Gd 2 (L) 6 (H 2 O)]·4H 2 O} n has the best corrosion inhibition properties for mild steel in 0.01 M NaCl. Furthermore, all a – g complexes are more effective corrosion inhibitors than the aqua and 2,2’‐bipyridine (bpy) complexes of unsubstituted phenylacetate indicating that 4‐OH substitution of phenylacetate enhances anti‐corrosion properties.