Magnetic and photo-physical properties of lanthanide dinuclear complexes involving the 4,5-Bis(2-pyridyl-N-oxidemethylthio)-4',5'-dicarboxylic acid-tetrathiafulvalene-, dimethyl ester ligand

Abstract

The reaction between the 4,5-bis(2-pyridyl-N-oxidemethylthio)-4',5'-dicarboxylic acid-tetrathiafulvalene-, dimethyl ester ligand (L) and the metallo-precursors Ln(hfac)3·2H2O leads to the formation of two dinuclear complexes of formula [Ln2(hfac)6(L)]·(CH2Cl2)·(C6H14)0.5 (LnIII = DyIII (1) and YbIII (2)). The X-ray structure reveals a quite regular square anti-prism symmetry for the coordination sphere of the lanthanide ion. UV-visible absorption properties have been experimentally measured and rationalized by TD-DFT calculations. The functionalization of the tetrathiafulvalene (TTF) core by two methyl ester moieties induces the appearance of an additional absorption band in the lowest-energy region of the spectrum. The latter has been identified as a HOMO (Highest Occupied Molecular Orbital)→ LUMO (Lowest Unoccupied Molecular Orbital) Intra-Ligand Charge Transfer (ILCT) transition in which the HOMO and LUMO are centred on the TTF and methyl ester groups, respectively. Irradiation at 22,222 cm-1 of this ILCT band induces an efficient sensitization of the YbIII-centred emission that can be correlated to the magnetic properties.