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 [Cu(2)Ln(mmi)(4)(NO3)(H2O)(2)](ClO4)(NO3)center dot 2H(2)O (Ln = Tb (2(.)Tb) or Gd (2G(.)d)) and [Cu2La(mmi)(4)(NO3)(2)(H2O)](ClO4)center dot 2H(2)O (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 mu-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 alpha 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 alpha value. The occurrence of a ferromagnetic interaction between Cu-II and Gd-III 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 Cu-II-Gd-III 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.