Crystal structure and magnetic properties of peacock–weakley type polyoxometalates Na9 [Ln(W5 O18)2] (Ln = Tm, Yb): Rare example of Tm(III) SMM

Abstract

We report Peacock–Weakley complexes, Na9 [Ln(W5 O18 )2 ]·35H2 O, formed with Tm(III), 1, and Yb(III), 2. Their syntheses, physico-chemical characterizations, crystal structures, and magnetic properties are described. Ab initio calculations are also reported. These polyoxometalate (POM) complexes were obtained using original synthetic conditions where acidification was performed with a stoichiometric amount of nitric acid to an acidity of Z = ν(H+ )/ν(WO42– ) = 8/10 = 0.80. Both the Tm(III) and Yb(III) derivatives were found to exhibit field-induced slow relaxation of their magnetization likely controlled by Raman and Orbach relaxation processes. 1 is a rare example of a Tm(III)-based single-molecule magnet (SMM) and is a consequence of the oblate tetragonal anti-prismatic symmetry of the coordination sphere.