Thiacalix[4]arene-supported mononuclear lanthanide compounds: slow magnetic relaxation in dysprosium and erbium analogues

Abstract

Four mononuclear lanthanide compounds, [Ln(TC4A-di-OMe)(L_OEt)] (Ln = Tb (1); Dy (2); Ho (3); Er (4)), were synthesized based on a thiacalix[4]arene derivative (H₂TC4A-di-OMe = 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,27-dihydroxy-26,28-dimethoxy thiacalix[4]arene) and one auxiliary ligand (L_OEt = (η⁵-cyclopentadienyl)tris-(diethylphosphito-p)cobaltate(III)). Compounds 1–4 were characterized using single crystal X-ray structural analysis and magnetization measurements. The Ln(III) ion features a seven-coordinated {LnO₇} environment, capped by one bowl-shaped thiacalix[4]arene ligand and one tripodal L_OEt ligand. Magnetic measurements reveal that dysprosium compound 2 shows a characteristic two-step relaxation process while erbium compound 4 behaves as a field-induced single-molecule magnet with a higher energy barrier at 31.7 K. The mononuclear erbium-based compound based on the macrocyclic multidentate thiacalix[4]arene ligand is rarely observed in molecular magnets.