Tetranuclear rare-earth complexes: energy barrier enhancement and two-step slow magnetic relaxation activated by ligand substitution

Abstract

The reaction of 5-(2-furanimino)-8-hydroxylquinoline (HL) and RE(dbm)₃·2H₂O (Hdbm = 1,3-diphenyl-1,3-propanedione) afforded [RE₄(dbm)₄(L)₆(μ₃-OH)₂] (RE = Y (1), Dy (2)), while under the same reaction conditions, but with the replacement of the co-ligand, another series of tetranuclear complexes, [RE₄(acac)₄(L)₆(μ₃-OH)₂]·(CH₃CN)_n (n = 2 for RE = Y (3), Dy (4), Ho (5); n = 0 for RE = Tb (6); Hacac = acetylacetone), were obtained. Alternating current susceptibility measurements reveal that 2 displays single-molecule-magnet behavior with an effective energy barrier of U_eff = 117.4 K (τ₀ = 1.79 × 10⁻⁸ s) under a zero direct-current field, while 4 presents two distinct slow magnetic relaxation processes with effective energy barriers of U_eff = 162.1 K for the fast relaxation (FR) process (τ₀ = 8.53 × 10⁻¹¹ s) and U_eff = 165.3 K for the slow relaxation (SR) process (τ₀ = 1.14 × 10⁻⁹ s), which demonstrates that subtle changes of the coordination environment can drastically influence the overall magnetic properties.