Tetrametallic Ln(III) (Ln = Gd, Dy) phosphonate clusters: Spin cooler and single-molecule magnet

Abstract We report herein convenient access to tetranuclear clusters of [Ln 4 ( R PO 3 ) 2 ( R PO 3 H)( t BuCO 2 ) 7 ( t BuCO 2 H) 3 (H 2 O) 3 ]·solvent Ln 4 (Ln = Gd, Dy), from dinuclear lanthanide precursors [Ln 2 (O 2 C t Bu) 6 (HO 2 C t Bu) 6 ] and a bulky phosphonate ligand (9-methyl-9 H -fluoren-9-yl)phosphonic acid ( R PO 3 H 2 ). In the structures of Ln 4 , 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 Gd 4 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 Dy 4 shows slow magnetic relaxation that is the character of a single-molecule magnet (SMM).