Lanthanide 5-sulfosalycilates and 3-amino-5-sulfosalycilates: Synthesis and estimation of thermal stability

•Several lanthanide 5-sulfo- and 3-amino-5-sulfosalycilates were synthesized.•The complexes were studied using thermogravimetric, IR and quantum chemical analysis.•Correlation between Ln–O bond energy and temperature of complexes decomposition was found.•Proposed application of these complexes as anti-exhaust additives to diesel oil.

Trivalent lanthanum, europium, terbium, erbium and lutetium 5-sulfosalycilates and terbium, europium and holmium 3-amino-5-sulfosalycilates have been synthesized with their composition studied using thermogravimetric, IR and quantum chemical analysis. Quantum chemical calculations were performed for anhydrous complexes. According to calculated data, coordination of La and Lu with 5-sulfosalycilic acid anion via carboxylic oxygen is more favorable compared to coordination via sulfonate oxygen, while the reverse situation is observed for Eu, Tb and Er 5-sulfosalycilates. In the case of Ho 3-amino-5-sulfosalycilate metal atom is coordinated by both groups while coordination via sulfonate group appears to be more preferable for Eu and Tb 3-amino-5-sulfosalycilates.A good correlation (R2 = 0.96) was found between calculated Ln–Oligand bond energy and temperature of complex decomposition, thus showing that semi-empirical methods can be used for preemptive estimation of thermal stability of lanthanide complexes. Synthesized compounds have potential as anti-exhaust additives to diesel fuel as their decomposition correspond with formation of soot particles, thus, inhibiting their growth.

Graphical abstractWe have found linear correlation between temperature of decomposition of synthesized lanthanide (Ln) 5-sulfosalycilates and 3-amino-5-sulfosalycilates and calculated Ln–O bond energies. Bond energies were calculated as: Ebond(Ln–O)=ΔHr/n,Ebond(Ln–O)=ΔHr/n, where ΔHr is heat of most probable reaction of complex formation; n – number of Ln–O bonds in said complex.Figure optionsDownload full-size imageDownload as PowerPoint slide