Lanthanide complexes involving multichelating TTF-based ligands

The reaction between the 2-{TTF-fused-1H-benzimidazol-2-yl}pyridine alkylated either with the di-(pyrazol-1-yl)-4-pyridyl (L1) or dimethyl-2,2’-bipyridine (L2) moiety and 1 equiv. of Ln(hfac)32H2O (LnIII = DyIII and YbIII) leads to three dinuclear complexes of formula [Yb2(hfac)6(L1)]2(CH2Cl2)·C6H14 (1) and [Ln2(hfac)6(L2)]CH2Cl2 (LnIII = YbIII (2) and DyIII (3)). The X-ray structures highlight square antiprism (D4d symmetry) and spherical tricapped trigonal prism (D3h) for the eight- and ninecoordinated lanthanide ions, respectively. Irradiation of the lowest-energy HOMO  LUMO ILCT absorption band induced a 2F5/2  2F7/2 Yb-centered emission for 1 and 2. Both YbIII ions displayed similar emissions in 2 while two distinct emissions were observed and attributed to the two YbIII ions in 1 depending on their coordination surroundings. Slow magnetic relaxation is detected by dynamic magnetic measurements for 3 with a measured relaxation time tau0 = 3.7(1.3) x 10-7 s and an energy barrier delta = 39.6(2) cm-1. Taking into account the environment of both DyIII 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.