Preparation of Rare Earth Complexes with Carboxylic Acids

1 Preparation of Rare Earth Complexes with Carboxylic Acids 

Many synthetic methods have been developed to prepare pure rare earth-carboxylic acid complexes with high yields. Based on the starting materials, the methods can be put into two categories (i) rare earth oxides and (ii) rare earth salts. The synthesis can be done in aqueous solutions, organic media, or mixtures of the two, depending on the solubility and the nature of the ligands and the complexes, under ambient conditions, by hydro(solvo)thermal synthesis, or by gel synthesis. Under hydro(solvo)thermal conditions (in aqueous or non-aqueous media 

1 Synthesis Starting with Rare Earth Oxides 

The synthesis is normally done under atmospheric pressure. By heating and/or refluxing the mixture of RE2O3 with a stoichiometric amount of R-COOH in water or an organic solvent, such as MeOH, EtOH, DME or DMSO, a clear solution of the complex can be obtained. The product can be harvested by filtration followed by evaporation of the solvents, or by adding a less-polar solvent to the solution. About 5% in excess of RE2O3 is typically used to avoid the possible contamination from the un-reacted R-COOH, and the unused RE2O3 can then be removed by filtration after the reaction is completed. 

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