Synthesis, Structures, and Magnetic Properties of Heteronuclear Cu(II)−Ln(III) (Ln = La, Gd, or Tb) Complexes

Facile one-pot reactions led to the formations of dinuclear [CuLn(hmp)2(NO3)3(H2O)2] (Ln = Tb (1·Tb), Gd (1·Gd),
or La (1·La)), and trinuclear [Cu2Ln(mmi)4(NO3)(H2O)2](ClO4)(NO3)·2H2O (Ln = Tb (2·Tb) or Gd (2·Gd)) and [Cu2La(mmi)4(NO3)2(H2O)](ClO4)·2H2O (2·La) with polydentate ligands 2-(hydroxymethyl)-pyridine and 2-hydroxymethyl-1-methyl-imidazole. In these complexes, each pair of Cu(II) and Ln(III) ions is linked by a double μ-alkoxo bridge.
The temperature dependences of the magnetic susceptibilities of 1 and 2 were investigated in the range of 2−300
K. The dinuclear and trinuclear Cu−Gd complexes exhibit ferromagnetic interaction. The coupling constant J values
in the heterodinuclear Cu−Gd complexes are correlated to values of the dihedral angles α between the two O−Cu−O
and O−Gd−O fragments of the bridging CuO2Gd networks, with the largest J value associated with the smallest
α value. The occurrence of a ferromagnetic interaction between CuII and GdIII ions of the trinuclear entity is supported
by the field dependence of the magnetization. The field dependence of the magnetization at 2 K of 1·Gd and 2·Gd
confirms the nature of the ground state and of the CuII−GdIII interaction, while alternating current susceptibility
measurements demonstrates out-of-phase ac susceptibility signals of 1·Tb, which is the molecule-based magnetic
material of the smallest nuclearity which exhibits frequency-dependent behavior within the 3d−4f mixed-metal systems.