Hetero-metallic {3d-4f-5d} complexes: preparation and magnetic behavior of trinuclear [(L^Me2Ni-Ln){W(CN)₈}] compounds (Ln=Gd, Tb, Dy, Ho, Er, Y; L^Me2=Schiff base) and variable SMM characteristics for the Tb derivative

Abstract

Assembling bimetallic {Ni-Ln}³⁺ units and {W(CN)₈}³⁻ is shown to be an efficient route toward heteronuclear {3d-4f-5d} compounds. The reaction of either the binuclear [{L^Me2Ni(H₂O)₂}{Ln(NO₃)₃}] complexes or their mononuclear components [L^Me2Ni] and Ln(NO₃)₃ with (HNBu₃)₃{W(CN)₈} in dmf followed by diffusion of tetrahydrofuran yielded the trinuclear [{L^Me2NiLn}{W(CN)₈}] compounds 1 (Ln=Y), 2a,b (Gd), 3a,b (Tb), 4 (Dy), 5 (Ho), and 6 (Er) as crystalline materials. All of the derivatives possess the trinuclear core resulting from the linkage of the {W(CN)₈} to the Ni center of the {Ni-Ln} unit. Differences are found in the solvent molecules acting as ligands and/or in the lattice depending on the crystallization conditions. For all the compounds ferromagnetic {Ni-W} and {Ni-Ln} (Ln=Gd, Tb, Dy, and Er} interactions are operative resulting in high spin ground states. Parameterization of the magnetic behaviors for the Y and Gd derivatives confirmed the strong cyano-mediated {Ni-W} interaction (J_NiW=27.1 and 28.5 cm⁻¹) compared to the {Ni-Gd} interaction (J_NiGd=2.17 cm⁻¹). The characteristic features for slow relaxation of the magnetization are observed for two Tb derivatives, but these are modulated by the crystal phase. Analysis of the frequency dependence of the alternating current susceptibility data yielded U_eff/k_B=15.3 K and τ₀=4.5×10⁻⁷s for one derivative whereas no maxima of X_M" appear above 2 K for the second one.