Element-Selective Molecular Charge Transport Characteristics of Binuclear Copper(II)-Lanthanide(III) Complexes.

A series of isostructural dinuclear 3d-4f complexes, isolated as [CuLn(L·SMe)2(OOCMe)2(NO3)]· xMeOH (Ln = Gd 1, Tb 2, Dy 3, and Y 4; x = 0.75-1) and comprising one acetate and two thioether-Schiff base (L·SMe-) bridging ligands based on 4-(methylthio)aniline and 2-hydroxy-3-methoxybenzaldehyde (HL·SMe = C15H15NO2S), was synthesized and fully characterized. The magnetic properties of the charge-neutral {CuLn} complexes are dominated by ferromagnetic CuII-LnIII exchange interactions. Large-area electron transport studies reveal that the average conductivity of robust, self-assembled {CuLn} monolayers on a gold substrate is significantly lower than that of common alkanethiolates. Theoretical calculations of transmission spectra of individual complexes 1 and 4 embedded between two metallic electrodes show that the molecular current-voltage ( I- V) characteristics are strongly influenced by electron transport through the Cu centers and thus fully independent of the lanthanide ion, in excellent agreement with the experimental I- V data for 1-4. The β-polarized transmission indicated by calculations of 1 and 4 points out their potential as spin filters. In addition, the reactivity of the title compound 1 with CuII in a square-pyramidal coordination environment toward methanolate and azide was examined, resulting in the formation of a linear trinuclear complex, [Cu2Na(L·SMe)4]NO3·3MeOH (5), characterized by antiferromagnetic exchange interactions between the two copper ions.