Conductance and stochastic switching of ligand-supported linear metal atom chains

Department of Chemistry, National Taiwan University* Department of Chemistry, National Tsing Hua University**
â—‹Shie-Ming Peng* I-Wen Peter Chen** Ming-Dung Fu** Wei-Hsiang Tseng** Jian-Yuan Yu** Sung-Hsun Wu** Chia-Jui Ku** Chun-hsien Chen**

Molecular wires and switches are projected the elemental building blocks for future electronic applications. Synthesizing one-dimensional molecules and comprehensively understanding their electric characteristics become one of the focus areas of contemporary material research. The growth of this research field is encouraged by discoveries of a strong dependence of electron transport on the length, conjugation, conformation, and substituents of the tailored molecules. While remarkable progress has been achieved during the past decade, most of the knowledge learned has been from conjugated organic molecules whose counterpart, organometallic molecular wires, has been rarely explored. Here we present quantitative measurements of single molecular conductance of one-dimensional multinuclear metal strings ([MnL4(NCS)2], Mn = Cr3, Co3, Ni3, Cr5, Co5, Ni5, and Cr7; L = oligo-a-pyridylamine). The conductance values are found correlated well with the d-orbital electronic coupling between adjoining metal atoms. Among the strings, penta- and heptachromium complexes exhibit stochastic switching events. Such multinuclear strings are important in setting up a perfect platform for the fundamental study of metal-metal interactions beyond dinuclear complexes. Crystallographic characterization up to nonanickel complex has been achieved and the length of ligands is extended to 11 repetitive pyridylamine units (m = 11). While purification and crystallization become increasingly challenging due to the nature of poorer solubility for longer oligomers, preliminary MALDI-MS spectra show that a string of 17 nickel ions (m = 7) is obtainable. An understanding of the conduction propagating along the metal chains will advance further towards molecular wires for nanodevices.