Solution state structure and equilibria of lanthanide (fod) 3 complexes revisited: A 1 H, 13 C and 19 F nuclear magnetic resonance study of Eu(fod) 3

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 CH 3 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 –d 27 chelate complexes already at relatively low (≥3.0 mg/0.4 ml) concentration.