Modulation of the magnetic and photophysical properties in 3d–4f and 4f–4f′ heterobimetallic complexes involving a tetrathiafulvalene-based ligand†

Abstract

The reaction between the 2-(1-(2,6-di(pyrazol-1-yl)-4-methylpyridyl)-4,5-(4,5-bis(propylthio)-tetrathiafulvalenyl)-1 H-benzimidazol-2-yl)-pyridine ligand (L), 1 equivalent of Ln(hfac) ₃·2H ₂O/Dy(tta) ₃·2H ₂O (hfac ⁻ = 1,1,1,5,5,5-hexafluoroacetylacetonate, tta ⁻ = 2-thenoyltrifluoroacetonate) and M(hfac) ₂·2H ₂O leads to the formation of heteroleptic 3d–4f dinuclear complexes of formula [MLn(hfac) ₅(L)] _n (M( ii) = Cd, Zn, Co, Mn, Ni and Ln( iii) = Dy, Yb, Nd) and [ZnDy(tta) ₂(hfac) ₃(L)]·(CH ₂Cl ₂). Their X-ray structures reveal that the two coordination sites are occupied by one Ln( iii) ion and one M( ii) transition metal respectively. The M( ii) ions are coordinated to the benzoimidazolylpyridine (bzip) moiety in a N ₂O ₄ coordination sphere, while the Ln( iii) ions are coordinated to the 2,6-di(pyrazol-1-yl)-4-pyridine (dpp) moiety in a N ₃O ₆ surrounding. When Dy( iii) ion is used a field-induced Single-Molecule Magnet (SMM) behavior is detected with a magnetic relaxation time slightly dependent to the nature of the vicinal divalent transition metal. On the other hand, when the Yb( iii) is used, intense, moderated or quenched ²F _5/2 → ²F _7/2 NIR luminescence is observed when the Yb( iii) ion is respectively associated with the Zn( ii), Mn( ii) and Ni( ii)/Co( ii) ion. The emission intensity can be modulated in function of the metal-to-ligand charge transfer and d–d transition intensities. The replacement of the divalent transition metal by a trivalent lanthanide leads to the formation of heteroleptic 4f–4f′ dinuclear complexes of formula [Ln _{2− x} Ln′ _x (hfac) ₆(L)]· a(CH ₂Cl ₂)· b(C ₆H ₁₄) and [Dy _1.11Nd _0.89(tta) ₃(hfac) ₃(L)]. The coordination selectivity is based on the radius. Among the 4f–4f′ series, the Dy( iii) derivatives displayed such ion in N ₂O ₆ eight-coordinated sphere allowing the observation of SMM behavior. The three compounds [Dy _1.21Nd _0.79(hfac) ₆(L)]·2(CH ₂Cl ₂)·(C ₆H ₁₄), [Yb _1.04Nd _0.96(hfac) ₆(L)] and [YbPr(hfac) ₆(L)] displayed respectively Nd( iii), modarated Yb( iii) and intense Yb( iii) NIR emissions.

Abstract

3d4f and 4f4f′ heterobimetallic complexes were designed thank to metal selective coordination with a redox-active tetrathiafulvalene-based ligand. Both magnetic and photophysical properties were investigated.