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 (IV) 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 IV data for 14. 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.