The synthesis and characterization of three isomorphous complexes [Ni(II)(L)Ln(III)(DBM)3] (Ln = Gd (·2.5CH3CN·0.5H2O), Tb (·2CH3CN·0.5MeOH), and Dy (·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 L(2-) contains an N2O2-inner and an O4-outer coordination site. There are diphenoxo bridges between Ni(II) and Ln(III) 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 . The magnetic coupling constant JNiGd in complex is estimated to be 1.11 cm(-1) (H = -2JNiGdSNiSGd). Alternating current (ac) magnetic susceptibility studies reveal that complexes and show frequency-dependent out-of-phase signals, which indicate that they exhibit SMM behavior. The energy barriers for complexes and under a 2 kOe applied direct current (dc) magnetic field are estimated from Arrhenius plots to be 14.4 and 11.3 K, respectively.