Ligands that can complex to lanthanides and selectively bind and sense them can improve our understanding of processes involved in nuclear separations, and also lead to future complexants for radiotoxic actinides in their trivalent form. In this study, pyrazole-based tripodal ligands based on the 1,3,5-tris(pyrazolyl)-2,4,6-triethylbenzene framework were used for sensing and extraction of lanthanides. This framework provides a highly organized cavity for cation binding that takes advantage of favorable positioning of coordination sites and potential cation-π interactions. Three such ligands were prepared and studied: One with unsubstituted pyrazole groups, one with dimethyl pyrazole groups, and one with diphenyl pyrazole groups. Binding and extraction of lanthanides in organic solvents were confirmed by fluorescence and NMR titrations. The 1,3,5-tris(3,5-dimethylpyrazolyl)-2,4,6-triethylbenzene ligand showed evidence of binding with several lanthanides both in UV-Vis spectra and in fluorescence titrations. 1H-NMR titrations also showed changes in chemical shift for all proton resonances, even for the diamagnetic La(III), indicating cation binding. Binding affinity was also determined by 1H-NMR from analysis of the binding isotherms derived from chemical shift changes. It was determined that the substitution on the pyrazole ring has a substantial effect both on binding strength, but also on the observed fluorescence emissions.

Spectroscopic study of lanthanide complexation by tripodal tris-(pyrazolyl) ligands

255th National Meeting (2018)

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