Synthesis, structure, and corrosion inhibiting properties of REIII 3-thiophenecarboxylate complexes

Abstract

Two series of Rare Earth (RE) 3-thiophencarboxylate (3TPC) complexes have been synthesized by metathesis reactions between a suitable RE salt and Na(3TPC). Single crystal X-ray diffraction determined that light rare earth metals yield nonacoordinate 1D polymeric complexes [Ln(3TPC)₃(H₂O)₃]_n (Ln = La (1a), Ce (1b), Pr (1c), Nd (1d), Sm (1e), Gd (1f)) while the heavier elements have a dimeric structure [Ln₂(3TPC)₆(H₂O)₄]·H₂O (Ln = Dy (2a), Ho (2b), Y (2c), Er (2d), Lu (2e)) with eight coordinated metal centers. Thermogravimetric analysis (TGA) and microanalysis data of all the compounds except for compound (2e) are consistent with the composition derived from single-crystal data. However, bulk compound [Lu₂(3TPC)₆(H₂O)₄]·H₂O (2e) lost both coordinated and lattice water during the drying process. Based on weight loss measurements, the corrosion inhibitory properties of the synthesized compounds on mild steel show that [Y₂(3TPC)₆(H₂O)₄]·H₂O (2c) has the greatest inhibition efficiency (68%). The potentiodynamic polarisation (PP) measurements are generally consistent with immersion test results. However, [Gd(3TPC)₃(H₂O)₃]_n (1f) exhibited a similar optimum value with an inhibitor efficiency of 70% utilizing this technique. The PP curves show that these compounds act predominantly as anodic inhibitors.