Acetato-bridged dinuclear lanthanide complexes with single molecule magnet behaviour for the Dy2 species

Abstract

Five dinuclear lanthanide complexes with formula [Ln₂L₂(OAc)₄(MeOH)_a(H₂O)_b]·cMeOH·dH₂O (a = 2, b = 0, c = 2, d = 0, Ln = Sm (1), Gd (2), Dy (3); a = 0, b = 2, c = 4, d = 2, Ln = Tm (4)) and [Yb₂L₂(OAc)₄(MeOH)₂]·[Yb₂L₂(OAc)₄(H₂O)₂]·2H₂O (5) (HL = (E)-N′-(2-hydroxybenzylidene)-2-mercaptonicotinohydrazide), have been synthesized and their crystal structures and magnetic properties are reported. All five complexes are centrosymmetric, showing a similar dinuclear core with two lanthanide ions in each complex being bridged by acetate groups in the η¹:η²:μ₂ mode. The various coordination modes of acetate groups result in two kinds of coordination geometries for Ln ions with the ones in complexes 1–4 and the Yb2 in 5 being nine-coordinated with a mono-capped square antiprism geometry, while the Yb1 ions in the other part of complex 5 are eight-coordinated with a triangular dodecahedron geometry. Magnetic susceptibility studies reveal that complex 3 shows single molecule magnet behaviour with an energy barrier of 39.1 K. In addition, comparison of the structural parameters among the similar Dy₂ SMMs with a η¹:η²:μ₂ coordination mode of carboxylate groups reveals the significant role played by coordination geometry in modulating the relaxation dynamics of SMMs.