Synthesis, structural characterization, and corrosion inhibition properties of rare earth 2-hydroxyphenylacetate coordination polymers

The salt metathesis reaction between sodium 2-hydroxyphenylacetate (Na(2hpa)) and a rare earth (RE) metal nitrate or chloride in an aqueous ethanol medium has yielded a series of rare earth one-dimensional (1-D) coordination polymers [La(2hpa) 3 (H 2 O) 2 ] n ( 1 ), {[RE 2 (2hpa) 6 (H 2 O) 4 ]⋅3.5H 2 O} n (RE = Ce ( 2 ), Nd ( 3 )), and {[RE 2 (2hpa) 6 (H 2 O) 2 ]·3H 2 O} n (RE = Gd ( 4 ), Dy ( 5 ), Y ( 6 ), Er ( 7), Yb ( 8) ) which have three different crystal structures. All structures were determined by single-crystal X-ray diffraction (XRD), except Y ( 6 ) and Yb ( 8 ) compounds, which were isomorphous with Gd ( 4 ), Dy ( 5 ), and Er ( 7 ) complexes by their unit cell parameters and X-ray powder diffraction (XRPD) patterns. Only the La complex ( 1 ) has a mononuclear repeating unit while the others are based on binuclear units. The chelating bridging carboxylate coordination mode is common for all complexes. In addition, complexes 1 – 3 exhibit the chelating mode with the 10-coordination number whereas complexes 4 – 8 have syn -syn-bridging bidentate binding with the coordination number of 9. In the weight loss anti-corrosion experiments, the {[Gd 2 (2hpa) 6 (H 2 O) 2 ]·3H 2 O} n ( 4 ) compound demonstrated the highest inhibition efficiency of 57 %. A significant difference between RE 2-hydroxyphenylacetate complexes and [Ce(salH) 3 (H 2 O)] n was usually not observed indicating little impact of the -CH 2 - unit between carboxylate and benzene ring. The reduced corrosion inhibition efficiencies of RE 2-hydroxyphenylacetate complexes compared with RE 4-hydroxyphenylacetates confirm the positive effect of the p -OH group on the benzene ring on anti-corrosion properties. The reaction between sodium 2-hydroxyphenylacetate (Na(2hpa)) and a rare earth (RE) metal nitrate or chloride in an aqueous ethanol medium has yielded a series of rare earth one-dimensional (1-D) coordination polymers. Only the La complex has a mononuclear repeating unit while the others (Ce, Nd, Gd, Dy, Y, Er and Yb) are based on binuclear units. The chelating bridging carboxylate coordination mode is common for all complexes. In the weight loss anti-corrosion experiments, the {[Gd 2 (2hpa) 6 (H 2 O) 2 ]·3H 2 O} n compound demonstrated the highest inhibition efficiency of 57 %. A significant difference between RE 2-hydroxyphenylacetate complexes and [Ce(Hsal) 3 H 2 O)] n was usually not observed indicating little impact of the -CH 2 - unit between carboxylate and benzene ring. • Rare earth 2-hydroxyphenylacetate complexes show a variety of structural types, but all being coordination polymers. • All complexes are one-dimensional coordination polymers but with differing coordination modes of the carboxylate to rare earth metal. • All complexes show intra-molecular hydrogen binding, while two structural types have inter-strand hydrogen bonding interactions. • All compounds show corrosion inhibition on mild steel in NaCl solution, with the best rare earth metal being gadolinium. • Compared with cerium salicylate we find the corrosion inhibition does not differ significantly when incorporating an extra -CH 2 - unit in the carboxylate arm.