Lanthanide hexafluoroacetylacetonates vs. nitrates for the controlled loading of luminescent polynuclear single-stranded oligomers†
This work demonstrates how minor structural and electronic changes between Ln(NO3)3 and Ln(hfac)3 lanthanide carriers (Ln = trivalent lanthanide, hfac = hexafluoroacetylacetonate) lead to opposite thermodynamic protocols for the metal loading of luminescent polynuclear single-stranded oligomers. Whereas metal clustering is relevant for Ln(hfac)3, the successive fixation of Ln(NO3)3 provides stable microspecies with an alternated occupancy of the binding sites. Partial anion dissociation and anion/ligand bi-exchange processes occur in polar aprotic solvents, which contribute to delay the unambiguous choice of a well-behaved neutral lanthanide carrier for the selective complexation of different trivalent lanthanides along a single ligand strand. Clues for further improvement along this stepwise strategy are discussed.