Modulating spin dynamics of binuclear LnIII–radical complexes by using different indazole radicals

摘要

The combination of LnIII ion (GdIII or DyIII) with two different indazole nitronyl nitroxide radicals results in four novel 2p–4f compounds, namely, [Ln(hfac)₃(5-IndazoleNIT)]₂ (Ln = Gd (1), Dy (2); hfac = hexafluoroacetylacetone; 5-IndazoleNIT = 5-(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)-1H-Indazole) and [Ln(hfac)₃(6-IndazoleNIT)]₂ (Ln = Gd (3), Dy (4); 6-IndazoleNIT = 6-(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)-1H-Indazole). Single crystal X-ray diffraction studies revealed that compounds 1–2 are binuclear isostructural complexes with local D_2d symmetry, in which each 5-IndazoleNIT molecule acts as a bridging ligand linking two LnIII ions through the oxygen atom of its NO group and nitrogen atom of its indazole ring to form a cyclic four-spin system. Complexes 3–4 exhibit analogous binuclear cyclic four-spin systems, where the symmetry of central LnIII ions is D_4d due to the change of location of the NO group in the indazole ring. In addition, compound 2 displays no out-of-phase alternating-current (ac) signal, whereas compound 4 exhibits obvious slow relaxation of magnetization, suggesting single-molecule magnet (SMM) behavior. The different magnetic relaxation behaviour between 2 and 4 is largely dependent on the ligand field of the central dysprosium ions.