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)-1H-benzimidazol-2-yl)-pyridine ligand (L), 1 equivalent of Ln(hfac)₃·2H₂O/Dy(tta)₃·2H₂O (hfac⁻ = 1,1,1,5,5,5-hexafluoroacetylacetonate, tta⁻ = 2-thenoyltrifluoroacetonate) and M(hfac)₂·2H₂O 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)]·(CH₂Cl₂). 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 N₂O₄ coordination sphere, while the Ln(III) ions are coordinated to the 2,6-di(pyrazol-1-yl)-4-pyridine (dpp) moiety in a N₃O₆ 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−xLn′_x(hfac)₆(L)]·a(CH₂Cl₂)·b(C₆H₁₄) 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 N₂O₆ eight-coordinated sphere allowing the observation of SMM behavior. The three compounds [Dy_1.21Nd_0.79(hfac)₆(L)]·2(CH₂Cl₂)·(C₆H₁₄), [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.