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.
Highlights
Since the discovery of the first mononuclear single molecule magnet (SMM) of lanthanide [1], f-elements have taken a preponderant place in the elaboration of coordination complexes in the field of molecular magnetism [2,3,4,5,6,7,8,9,10,11]
L can be described as a multiply functionalized ligand with two pyridine-N-oxide moieties that are suitable for the coordination of lanthanide ions, leading generally to the formation of dinuclear complexes on one side and two ester groups on the other side, whose electron-withdrawing character will monitor the ligand’s electronic properties
The analysis of the polyhedron symmetry around the metallic centres reveals that the dinuclear complexes of the present work have the most symmetric coordination sphere compared to the previously published dinuclear compounds
Summary
Since the discovery of the first mononuclear single molecule magnet (SMM) of lanthanide [1], f-elements have taken a preponderant place in the elaboration of coordination complexes in the field of molecular magnetism [2,3,4,5,6,7,8,9,10,11]. The very weak intensity of the f–f absorption bands (Laporte forbidden) [30] makes a direct excitation less straightforward, and lanthanide ions are usually coordinated to an organic ligand that strongly absorbs light in the UV-visible range. This organic ligand plays the role of organic chromophore for the sensitization of the lanthanide’s luminescence through an antenna effect [31,32].
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