Metal ion independent conductance through bis-chelated metal complex molecular wires based on a bis(diphenylphosphino)aniline derivative

Abstract

It is becoming increasingly evident that transition metal complexes impart desirable qualities in single-molecule electronics, and testing metallic centres in combination with appropriate ligands is salient to building the next generation of single-molecule devices. Metal-phosphine complexes have been the subject of very few studies, despite their extensive use in other areas of chemistry. In this contribution, we fabricated and studied robust single-molecule junctions using linear bis-chelated ligand–metal–ligand complexes of the type [M(PNP)₂]PF₆ (M = Cu(I), Ag(I) or Au(I); PNP = bis(diphenylphosphino)aniline functionalised with methylthio contact groups). The robustness of the devices was evinced by surface-enhanced Raman spectroscopy (SERS) and scanning-tunnelling microscopy break junction (STM-BJ) methods, and the conductance of the devices was found to be independent of the central transition metal. Quantum transport calculations show consistent HOMO–LUMO gaps between the studied complexes in the transmission plots, supporting the experimental findings. This study shows that bis-chelation is a viable approach to the fabrication of stable and robust metal-phosphine devices.