Alizarin complexone-lanthanide(III)-fluoride system: Revised speciation and the origin of the analytical signal

作者：Martinez Vargas Sergio; Gomez Tagle Paola; Yatsimirsky Anatoly K^*

来源：Inorganica Chimica Acta, 2011, 373(1): 226-232.

DOI：10.1016/j.ica.2011.04.024

• Alizarin complexone
• Lanthanide
• Fluoride
• Potentiometry
• Ternary complexes

Potentiometric titrations of alizarin complexone (ALC) in the presence of La(III), Eu(III) and Y(III) in 50% vol. DMSO reveal formation of mostly binuclear complexes with monoprotonated (LH) and completely deprotonated (L) forms of the ligand of the type M(2)L(2)H(2), M(2)L(2)H and M(2)L(2). Only for La(III) a single mononuclear complex LaLH is observed in acidic media. Titrations of the same mixtures with added fluoride show that with Eu(III) and Y(III), fluoride forms ternary complexes without shifting the distribution profile of complexes with differently protonated forms of bound ALC, but with La(III) a strong shift in distribution in favor of complexes with the deprotonated ligand occurs, which explains the appearance of blue colored species in acidic medium giving rise to the analytical signal employed for quantitative determination of fluoride. Detailed analysis of the spectral properties of La(III)-ALC-fluoride system on the basis of the established species distribution diagrams demonstrate the following factors to be involved: (1) fluoride-induced conversion of LaLH to La(2)L(2)HF around pH 3; (2) anomalously high affinity of La(III)-ALC complexes to fluoride and (3) some sort of mutual effect of fluoride and ALC ligands in ternary La(III) complexes, probably involving change in the metal coordination number, leading to enhanced absorptivity of La(2)L(2)HF as compared to La(2)L(2)H.

• 出版日期2011-7-15