Heterodinuclear MII–LnIII single molecule magnets constructed from exchange-coupled single ion magnets

Abstract

The synthesis and characterization of four dinuclear 3d–4f complexes [M^IILn^III(L)(DBM)₃] (ZnDy = 1, CoY = 2, CoDy = 3·3.5CH₃CN, CoGd = 4·3.5CH₃CN) are reported (H₂L = N,N′-dimethyl-N,N′-(2-hydroxy-3-methoxy-5-methyl-benzyl)ethylenediamine, DBM⁻ = anion of 1,3-diphenyl-propane-1,3-dione). In each of the four complexes, the M^II ion occupies the internal N₂O₂ site whereas the Ln^III ion occupies the external O₄ site. There are diphenoxo bridges between the M^II and Ln^III ions in these complexes. The remaining coordination sites are occupied by three DBM⁻ anions. Direct current (dc) magnetic susceptibility measurements indicate the presence of intramolecular ferromagnetic interactions in complexes 3 and 4. The magnetic coupling constant, J_CoGd, of complex 4 is estimated to be 0.26 cm⁻¹ (H = −2J_CoGdS_CoS_Gd). Alternating current (ac) magnetic susceptibility studies reveal that complexes 1 and 2 show field-induced single molecule magnet behavior, with ΔE values of 36.5 K and 8.56 K, respectively. Complex 3 shows frequency dependent out-of-phase signals, indicating the presence of a slow relaxation of the magnetization, whereas complex 4 does not display slow magnetization relaxation.