Lanthanide complexes involving multichelating TTF-based ligands

Abstract

The reaction between the 2-{TTF-fused-1H-benzimidazol-2-yl}pyridine alkylated with either the di-(pyrazol-1-yl)-4-pyridyl (L¹) or dimethyl-2,2′-bipyridine (L²) moiety and 1 equiv. of Ln(hfac)₃·2H₂O (Ln^III = Dy^III and Yb^III) leads to three dinuclear complexes of formula [Yb₂(hfac)₆(L¹)]·2(CH₂Cl₂)·C₆H₁₄ (1) and [Ln₂(hfac)₆(L²)]·CH₂Cl₂ (Ln^III = Yb^III (2) and Dy^III (3)). The X-ray structures highlight square antiprism (D_4d symmetry) and spherical tricapped trigonal prism (D_3h) for the eight- and nine-coordinated lanthanide ions, respectively. Irradiation of the lowest-energy HOMO → LUMO ILCT absorption band induced a ²F_5/2 → ²F_7/2 Yb-centered emission for 1 and 2. Both Yb^III ions displayed similar emissions in 2 while two distinct emissions, attributed to the two Yb^III ions because of their different coordination environments, were observed in 1. Slow magnetic relaxation is detected by dynamic magnetic measurements for 3 with a measured relaxation time τ₀ = 3.7(1.3) × 10⁻⁷ s and an energy barrier Δ = 39.6(2) cm⁻¹. Taking into account the environment of both Dy^III ions in 3, it was expected that both metallic centers displayed similar dynamic magnetic behavior. The latter was rationalized by ab initio CASSCF/SI-SO calculations.