In search of structure–function relationships in transition-metal based rectifiers

Abstract

Heterometallic chains have been proposed as potential current rectifiers in molecular electronics, their left–right asymmetry providing, at least in principle, a mechanism for differentiation of current flow in forward and reverse directions. Here we compare two known extended metal atom chains (EMACs), Ru₂Ni(dpa)₄(NCS)₂ and Ru₂Cu(dpa)₄(NCS)₂, both of which meet the first criterion for rectification in so much as they are physically asymmetric. In both cases the dominant transport channel is a doubly degenerate π* orbital localised, to a first approximation, on the Ru₂ unit. As a result, current is limited by tunnelling across the Au–SCN–Ni/Cu junction. The paramagnetic Ni centre tunes the left–right delocalisation of the channel, making the minority-spin (β) channel more transparent than its spin-α counterpart and this difference provides the basis for asymmetry in the current under forward and reverse bias.