LAUSR

Abstract We report herein convenient access to tetranuclear clusters of [Ln4(RPO3)2(RPO3H)(tBuCO2)7(tBuCO2H)3(H2O)3]·solvent Ln4 (Ln = Gd, Dy), from dinuclear lanthanide precursors [Ln2(O2CtBu)6(HO2CtBu)6] and a bulky phosphonate ligand (9-methyl-9H-fluoren-9-yl)phosphonic acid (RPO3H2). In the structures of Ln4, four Ln(III) ions are arranged at the vertices of an irregular quadrilateral that are wrapped by bulky hydrophobic fluorenyl groups. Magnetic studies show that Gd4 exhibits high magnetocaloric effect (MCE) with entropy change of 23.10 J kg−1 K−1 at 2.5 K for ΔH = 7 T, while Dy4 shows slow magnetic relaxation that is the character of a single-molecule magnet (SMM).