Strategies to enhance signal intensity with paramagnetic fluorine-labelled lanthanide complexes as probes for ¹⁹F magnetic resonance

The synthesis and ¹⁹F NMR spectroscopic properties are reported for three series of CF₃-labelled lanthanide(iii) complexes, based on mono- and diamide cyclen ligands. Analyses of variable temperature, pH and field ¹⁹F, ¹⁷O and ¹H NMR spectroscopic experiments are reported and the merits of a triphosphinate mono-amide complex defined by virtue of its favourable isomer distribution and attractive relaxation properties. These lead to an enhanced sensitivity of detection in ¹⁹F magnetic resonance experiments versus a diamagnetic Y(iii) analogue, paving the way for future shift and imaging studies.