Lanthanide Dinuclear Complexes Involving Tetrathiafulvalene-3-pyridine-N-oxide Ligand: Semiconductor Radical Salt, Magnetic, and Photophysical Studies

Centro-symmetric dinuclear complexes of formula [Ln­(tta)3(L)]2·xCH2Cl2, (tta– = 2-thenoyltrifluoroacetonate
anion, x = 0.5 for Ln = Eu (1a), Tb
(3), and Dy (4) and x =
0 for Ln = Eu (1b) and Nd (2)) have been
synthesized using the tetrathiafulvalene-3-pyridine-N-oxide as a bridging ligand (L). X-ray structures have
shown the formation of channels with CH2Cl2 solvent
inside. 1 is stable with both filled channels (at 150
K) and empty channels (at room temperature). The DyIII analogue
displays a complex butterfly like hysteresis loop at 1.5 K. Photophysical
properties of the coordination complexes have been studied by solution
and solid-state absorption spectroscopy. Time-dependent density functional
theory (TD-DFT) calculations have been carried out on the diamagnetic
YIII derivative to shed light on the absorption spectrum.
For 2, the excitation of the charge transfer transitions
induces line shape emission in the near-infrared spectral range assigned
to 4F3/2→ 4I9/2, 4F3/2→ 4I11/2, and 4F3/2→ 4I13/2 neodymium centered transitions. The reversible redox-activity of
the ligand L makes possible an original sensitization
process involving a ligand centered charge separation followed by
energy transfer to the NdIII ion upon recombination.