High Electrical Conductivity of Single Metal–Organic Chains

Molecular wires are essential components for future nanoscale electronics.
However, the preparation of individual long conductive molecules is still a
challenge. MMX metal–organic polymers are quasi-1D sequences of single
halide atoms (X) bridging subunits with two metal ions (MM) connected by
organic ligands. They are excellent electrical conductors as bulk macroscopic
crystals and as nanoribbons. However, according to theoretical calculations,
the electrical conductance found in the experiments should be even higher.
Here, a novel and simple drop-casting procedure to isolate bundles of few to
single MMX chains is demonstrated. Furthermore, an exponential dependence
of the electrical resistance of one or two MMX chains as a function of
their length that does not agree with predictions based on their theoretical
band structure is reported. This dependence is attributed to strong Anderson
localization originated by structural defects. Theoretical modeling confirms
that the current is limited by structural defects, mainly vacancies of iodine
atoms, through which the current is constrained to flow. Nevertheless, measurable
electrical transport along distances beyond 250 nm surpasses that of
all other molecular wires reported so far. This work places in perspective the
role of defects in 1D wires and their importance for molecular electronics.