Synthesis and characterization of heterodinuclear Ln3+-Fe3+ and Ln3+-Co3+ complexes, bridged by cyanide ligand (Ln3+ = lanthanide ions).: Nature of the magnetic interaction in the Ln3+-Fe3+ complexes

The reaction of Ln(NO3)(3).aq with K-3[Fe(CN)(6)] Or K-3[Co(CN)(6)] in N,N'-dimethyltormamide (DMF) led to 25 heterodinuclear [Ln(DMF)(4)(H2O)(3)(mu-CN)Fe(CN)(5)]-nH(2)O and [Ln(DMF)(4)(H2O)(3)(mu-CN)Co(CN)(5)].nH(2)O complexes (with Ln = all the lanthanide(III) ions, except promethium and lutetium). Five complexes (Pr3+-Fe3+), (Tm3+-Fe3+), (Ce3+-Co3+), (Sm3+-Co3+), and (Yb3+-Co3+) have been structurally characterized; they crystallize in the equivalent monoclinic space groups P2(1)/c or P2(1)/n. Structural studies of these two families show that they are isomorphous. This relationship in conjunction with the diamagnetism of the Co3+ allows an approximation to the nature of coupling between the iron(III) and the lanthanide(III) ions in the [Ln(DMF)(4)(H2O)(3)(mu-CN)Fe(CN)(5)]-nH(2)O complexes. The Ln(3+)-Fe3+ interaction is antiferromagnetic for Ln = Ce, Nd, Gd, and Dy and ferromagnetic for Ln = Tb, Ho, and Tm. For Ln = Pr, Eu, Er, Sm, and Yb, there is no sign of any significant interaction. The isotropic nature of Gd3+ helps to evaluate the value of the exchange interaction.