Periodic trends in electron transport through extended metal atom chains: comparison of Ru3(dpa)4(NCS)2 with its first-row analogues

Abstract

Density functional theory is used to reconcile the structural, magnetic and electron transport properties of a triruthenium extended metal atom chain, Ru₃(dpa)₄(NCS)₂. The distinct bending of the Ru–Ru–Ru core in this species is traced to strong second-order mixing between levels of σ and π symmetry that are near degenerate in the linear geometry. The dominant electron transport channel is formed by the LUMO, an orbital of π* symmetry that lies just above the Fermi level of the gold electrode. The bending has a substantial impact on electron transport in that it induces a spin crossover from a quintet to a singlet which in turn brings the LUMO much closer to the Fermi level. The presence of significant net π bonding in the metal chains also broadens the π/π^nb/π* manifold, such that the channel is not strongly perturbed by the electric field, even at a bias of 1.0 V. The presence of a robust π symmetry conduction channel marks the triruthenium systems out as quite distinct from its first-row counterparts, Cr₃(dpa)₄(NCS)₂ and Co₃(dpa)₄(NCS)₂, where current flows primarily through the σ framework.