Structural and spectroscopic investigations of nine-coordinate redox active lanthanide complexes with a pincer O,N,O ligand

The lanthanide complexes EuL 3 , GdL 3 , YbL 3 and LuL 3 of the N , N ′-bis(2-hydroxy-di-3,5- tert -butylphenyl)amine were prepared. The X-Ray crystal structures of GdL 3 and LuL 3 demonstrated a nine-coordinate sphere with three ligand molecules under their anionic diamagnetic form (Cat-N-BQ) − . The complexes showed three oxidation events ( E ox1 1/2 = 0.15-0.16 V, E 1/2 2 = 0.51-55 V, and E 1/2 3 = 0.75-0.78 V vs. Fc + /Fc) via cyclic voltammetry, corresponding to the successive oxidation of the aminophenolate moeities to iminosemiquinone species. The complexes GdL 3 and YbL 3 were characterized by EPR spectroscopy, allowing for the determination of the zero field splitting (ZFS) parameters in the first case. The monocations (LnL 3 ) + and monoanions (LnL 3 ) − were electrochemically generated (Ln = Eu, Gd, Yb, Lu), as well as the dications YbL 3 2+ and LuL 3 2+ . The spins are antiferromagnetically exchange coupled in the diradical species LuL 3 2+ (| D | = 260 MHz, E = 0). All the complexes (incl. neutral) possess a strong absorption band in the NIR region (730-840 nm, > 19 mM −1 cm −1 ) corresponding to ligand-based transitions. Three ligand molecules coordinate under their anionic diamagnetic form; the complexes (Gd, Eu, Yb, Lu) can undergo reversible oxidations, affording radical species, as demonstrated by spectro-electrochemistry.