High Nuclearity Complexes of Lanthanide Involving Tetrathiafulvalene Ligands: Structural, Magnetic, and PhotoPhysical Properties

The reaction between the tetrakis­(2-pyridyl-N-oxidemethylthio)­tetrathiafulvalene ligand (L) and Ln­(hfac)3·2H2O precursors (where hfac– = 1,1,1,5,5,5-hexafluoroacetylacetonate anion and Ln = TbIII (1), DyIII (2), ErIII (3), and YbIII (4) and (4b)) leads to the formation of five tetranuclear complexes
of formula [Ln4(hfac)12(L)2]n·xCHCl3·yC6H14 (n = 1, x = 2, y = 0 for
(1), (2), and (4), n = 1, x = 4 for (3), and n = 2, x = 2.5, y = 1
for (4b)). Their X-ray structures reveal that the surrounding
of each LnIII center is filled by two N-oxide groups coming from two different ligands L. These
tetranuclear complexes have the highest nuclearity which is reported
until now for coordination compounds of lanthanide involving TTF-based
ligands. Direct current (dc) measurements highlight the paramagnetic
behavior of the compounds with a significant crystal field effect.
The temperature dependences of static magnetic measurements for 4 have been fitted. The ground state corresponds to MJ = ±5/2 while the first
excited state (MJ = ±3/2)
was localized at +214 cm–1 which was well correlated
with the luminescence transition. UV–visible absorption properties
have been experimentally measured and rationalized by time-dependent
density functional theory (TD-DFT) calculations. Upon irradiation
at 77 K and room temperature, in the range 24390–20835 cm–1, both compounds 3 and 4 display a metal-centered luminescence attributed to 4I13/2 → 4I15/2 (6660 cm–1) and 2F5/2 → 2F7/2 (signal centered around the value of 9966 cm–1) transitions, respectively. The observed six transitions
could be attributed to the MJ state splitting due to the existence of two Yb1 and Yb2 ions
with slightly different polyhedra in 4.