Study of crylene acid ligand coordinated to lanthanide compound

Carboxylic acids are commonly used in coordination chemistry with lanthanides ions, owing to the stronger binding to metal centre. In this work we report the coordination of crylene acid (CLN; 2-cyano-3,3-diphenyl-2-propenoic acid). According to our previous studies, CLN (Figure 1) is a chromophore obtained from the alkaline hydrolysis of octocrylene (OCR; 2-ethylhexyl 2-cyano-3,3-diphenyl-2-propenoate), as known there is no studies reporting lanthanide coordination compounds of CLN ligand. We report here the synthesis and characterization of lanthanide (gadolinium and europium) complex, LnCLN, due to: Possibility of determining ligand triplet state by GdCLN fluorescence analysis; Low cost of Gd compared with other Ln3+; Similarity between Gd3+ and Eu3+ atomic radii; On other hand Eu3+ complexes exhibit narrow bands and can be used as structural probe. To obtain LnCLN, 4.0 mmol CLN was solubilized in ethanol, 1.0 mmol LnCl3 (pH 4.5) was slowly added to the solution. The system was kept in stirring and heating for ~1 h at 50 °C. After some days a solid (Figure 2) were obtained, filtered out, washed with ethanol and dried in a vacuum. FT-IR spectra of LnCLN compared with CLN ligand (Figure 3), show a s(C=O) band displacement of ~76 cm-1 suggesting strong interaction between oxygen atoms from carbonyl groups and Ln3+. The chemical stoichiometry of the complex, suggested by Ln3+ titration using a standard EDTA solution, confirmed the 1:3 (metal:ligand) molar ratio. To verify charge transfer, CLN triplet state will be determined by GdCLN fluorescence analysis.