Synthesis, crystal structure and magnetic properties of dinuclear NiIILnIII complexes based on a flexible polydentate ligand.

The synthesis and characterization of three isomorphous complexes [NiII(L)LnIII(DBM)₃] (Ln = Gd (1·2.5CH₃CN·0.5H₂O), Tb (2·2CH₃CN·0.5MeOH), and Dy (3·2CH₃CN·0.5MeOH·0.5H₂O)) are reported (H₂L = N,N'-dimethyl-N,N'-(2-hydroxy-3-methoxy-5-methylbenzyl)ethylenediamine, DBM⁻ = anion of 1,3-diphenylpropane-1,3-dione). The flexible ligand L²⁻ contains an N₂O₂-inner and an O₄-outer coordination site. There are diphenoxo bridges between NiII and LnIII ions in these complexes. The remaining coordination sites are occupied by DBM⁻ anions. Direct current (dc) magnetic susceptibility measurements indicate the presence of intramolecular ferromagnetic interactions in desolvated complexes 1-3. The magnetic coupling constant JNiGd in complex 1 is estimated to be 1.11 cm⁻¹ (H = -2JNiGdSNiSGd). Alternating current (ac) magnetic susceptibility studies reveal that complexes 2 and 3 show frequency-dependent out-of-phase signals, which indicate that they exhibit SMM behavior. The energy barriers for complexes 2 and 3 under a 2 kOe applied direct current (dc) magnetic field are estimated from Arrhenius plots to be 14.4 and 11.3 K, respectively.