In a qualitative approach, variable temperature 1 H, 19 F and 13 C nuclear magnetic resonance (NMR) were used to characterize the solution state structure and equilibria of the widely used lanthanide solvent reagent Eu(fod)3 . Despite the fact that the side chain fluorines are far from the coordination site, the 19 F-1 H NMR spectra turned out to be sensitive reporters of self-coordination and/or adduct formation with other ligands. For example, they predict/explain immediately the otherwise hardly predictable magnitude of the expectable paramagnetic effects. The temperature-dependent Fermi-contact effects observed in the 13 C{1 H} spectra were extremely important aides in their assignments. The equilibria could be manipulated by changing the solvent used and/or the reagent/ligand molar ratio. Depending on their coordination ability, the solvents possess a certain control over the adduct life times. Sharpening of the 19 F signals in the presence of associative solvent molecules such as dimethyl sulfoxide (DMSO) or CH3 CN is an indication of changing complex structure (shifting the equilibrium towards the monomeric form). In apolar solvents, relaxation and diffusion data confirmed the oligomerization of the Eu(fod)3 -d27 chelate complexes already at relatively low (≥3.0 mg/0.4 ml) concentration.
Keywords: 13C; 19F; Eu(fod)3; LSR; NMR; complexation equilibria; self-association; solvent effect.
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