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)<sub>2</sub>­(OOCMe)<sub>2</sub>(NO<sub>3</sub>)]·<i>x</i>MeOH (Ln = Gd <b>1</b>, Tb <b>2</b>, Dy <b>3</b>, and Y <b>4</b>; <i>x</i> = 0.75–1) and comprising one acetate and two thioether-Schiff base (L·SMe<sup>–</sup>) bridging ligands based on 4-(methylthio)­aniline and 2-hydroxy-3-methoxybenzaldehyde (HL·SMe = C<sub>15</sub>H<sub>15</sub>NO<sub>2</sub>S), was synthesized and fully characterized. The magnetic properties of the charge-neutral {CuLn} complexes are dominated by ferromagnetic Cu<sup>II</sup>–Ln<sup>III</sup> 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 <b>1</b> and <b>4</b> embedded between two metallic electrodes show that the molecular current–voltage (<i>I</i>–<i>V</i>) 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>I</i>–<i>V</i> data for <b>1</b>–<b>4</b>. The β-polarized transmission indicated by calculations of <b>1</b> and <b>4</b> points out their potential as spin filters. In addition, the reactivity of the title compound <b>1</b> with Cu<sup>II</sup> in a square-pyramidal coordination environment toward methanolate and azide was examined, resulting in the formation of a linear trinuclear complex, [Cu<sub>2</sub>Na­(L·SMe)<sub>4</sub>]­NO<sub>3</sub>·3MeOH (<b>5</b>), characterized by antiferromagnetic exchange interactions between the two copper ions.