Goblet-shaped pentanuclear lanthanide clusters assembled with a cyclen derivative ligand exhibiting slow magnetic relaxation
Two coordination compounds with the formula Ln5(H2O)(OH)4(NO3)3(BZA)4L (Ln = Tb3+ (1), Dy3+ (2)) have been assembled in a one-pot synthesis from the tetrasubstituted cyclen derivative ligand N,N′,N′′,N′′′-tetra(2-hydroxy-3-methoxy-5-methylbenzyl)-1,4,7,10-tetraazacyclododecane (H4L), Ln(NO3)3·xH2O (Ln = Tb3+ (x = 6), Dy3+ (x = 5)) and the auxiliary ligand benzoic acid (HBZA). Single-crystal X-ray diffraction studies reveal that both compounds feature a novel homometallic appended cubane geometry. The magnetic study on 1 suggests the presence of anti-ferromagnetic interactions, whereas 2 exhibits weak ferromagnetic coupling. Under an applied dc field, 1 shows no out-of-phase alternating current (ac) signal whereas 2 shows slow-relaxation processes that correspond to an energy gap (Ea/kB) of 4.11 K and a pre-exponential factor (τ0) of 3.45 × 10−5 s.