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 (E_a/k_B) of 4.11 K and a pre-exponential factor (τ₀) of 3.45 × 10⁻⁵ s.