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

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 [Ln(2)(3TPC)(6)(H2O)(4)]center dot 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 [Lu-2(3TPC)(6)(H2O)(4)]center dot 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 [Y-2(3TPC)(6)(H2O)(4)]center dot 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)], (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.

Automated summary

Two series of rare earth thiophencarboxylate complexes have been synthesized and their crystal structures have been determined using X-ray diffraction. Thermogravimetric analysis and microanalysis data confirm the composition of the compounds derived from single-crystal data, except for one compound which loses coordinated and lattice water during the drying process. The corrosion inhibitory properties of the synthesized compounds on mild steel show that one compound exhibits the highest inhibition efficiency. Potentiodynamic polarization measurements are consistent with immersion test results, showing that these compounds act predominantly as anodic inhibitors.