Compactly Fused o‐Quinone‐Extended Tetrathiafulvalene‐o‐Quinone Triad – a Redox‐Amphoteric Ligand

Abstract

A new redox‐amphoteric ligand comprising a p‐phenylene‐extended tetrathiafulvalene (TTF) core and two o‐quinone termini has been synthesized. This work was performed in an attempt to synthesize a bridging ligand by combining one of the most powerful organic donors with strong acceptor units in a single molecule. The product was isolated in the doubly reduced diprotonated form. An X‐ray diffraction study revealed a rigid and planar structure for this molecule. This is the first example of an air‐stable p‐phenylene‐extended TTF with an unprotected central ring. The diquinone form itself has been prepared by oxidation of the doubly reduced diprotonated species and then characterized in solution. The electronic spectrum of this compound contains an intense peak that corresponds to intramolecular charge transfer. The spectroscopic and structural studies of both compounds were accompanied by DFT calculations. A singlet biradical ground state was predicted for the doubly reduced diprotonated form.

Field-Induced Dysprosium Single-Molecule Magnet Involving a Fused o-Semiquinone-Extended-Tetrathiafulvalene-o-Semiquinone Bridging Triad

“…The two protonated oxygen atoms (O2 and O3) remain uncoordinated. The bridging ligand in 1 is almost planar, and its structure is very similar to that of the free ligand in its protonated semiquinone form [22]. In fact, the torsion angle between the planes defined by the benzo-1,3-dithio system and the p-phenylene ring takes the average value of 6.32 (11) • , which can be compared with the value of 8.70 (10) • found for the free L ligand.…”

“…The arrangement of the ligands around the Dy III center leads to an O8 surrounding with a coordination polyhedron symmetry intermediate between the C2v biaugmented trigonal prism (CShMBTPR-8 = 1.140), the D4d square antiprism (CShMSAPR- The crystal packing of 1 is shown in Figure 2. No significant intermolecular interactions, such as S···S, S···O, or π···π interactions, as observed in the X-ray structure of the free ligand L [22], were identified. The L triad and Dy(hfac) 3 metallo-precursor formed two subnetworks aligned along the c-axis (Figure 2).…”

“…The crystal packing of 1 is shown in Figure 2. No significant intermolecular interactions, such as S···S, S···O, or π···π interactions, as observed in the X-ray structure of the free ligand L [22], were identified. The L triad and Dy(hfac)3 metallo-precursor formed two subnetworks aligned along the caxis (Figure 2).…”

“…Along these lines, we proposed to replace the TTF core with p-phenylene-extended TTF to lower the HOMO-LUMO gap, because the first oxidation potential is lower than for TTF [21], and to stabilize the protonated semiquinone form, which might offer a dissymmetric coordination site and thus give the possibility to reach new molecular systems. The coordination reaction between [Dy(hfac)3]·2H2O (hfac − refers to 1,1,1,5,5,5-hexafluoroacetylacetonate) and the 2,2′-benzene-1,4-diylbis(6-hydroxy-4,7-di-tert-butyl-1,3-benzodithiol-2-ylium-5-olate biradical triad [22] (L) (Scheme 1) led to the formation of the {[Dy(hfac)3(L)]·2C6H14}n (1) polymer. The X-ray structure and photophysical and magnetic properties were studied.…”

“…The 2,2′-benzene-1,4-diylbis(6-hydroxy-4,7-di-tert-butyl-1,3-benzodithiol-2-ylium-5-olate biradical triad (L) (Scheme 1) was previously synthesized starting from a 2:1 4-chloro-3,6-di-tertbutyl-o-benzoquinone and sodium tetrathioterephthalate mixture in tetrahydrofuran (THF) [22]. This triad was previously studied by open-shell density functional theory calculations, which revealed that the broken-symmetry (BS) state in a global minimum is singlet biradical according to the spin density distribution.…”