Smallest Electrical Wire Based on Extended Metal-Atom Chains

Abstract

An ideal electrical wire needs not only good conductivity for its central conductor but also a surrounding insulating layer to protect its current from leaking. We show that the extended metal-atom chain is a promising candidate to be the smallest molecular electrical wire for future practical applications. The electron can move through core metals, while the internal current is insulated from outside by the surrounding π-conjugated functional group. Moreover, we also show the existence of unavoidable hidden pathways at each site to the electrodes in a nanoscaled quantum circuit. Nevertheless, the Kirchhoff's junction rule still holds when the current inflow and outflow arising from the additional terms of the self-energies of contacts are included.It is an important issue to find potential single molecular wires that can be functional units of nanotransistors for electronic apparatus application. 1 The current understanding of the electron transfer through a single molecular wire is mainly built on organic molecules with and without π-electron conjugated systems. [2][3][4] People have realized that in order to reach high conductivity the delocalized electrons in the bridge are needed to play the role of charge transfer. Pure organic molecules such as oligo(phenylene ethynylene) (OPE) 5 and oligo(phenylene vinylene) (OPV) 6 are often discussed for their long π-conjugated chains. However, in the fabrication of nanodevices, it is unavoidable to have multiple molecular wires packed in proximity. The wave function of one conductor can mix with the other through the overlap of electron clouds, which may result in the unwanted transversal hopping of charge carriers. In view of this, one-dimensional metal string complexes 7 can be a promising candidate without the above problem.Extended metal-atom chain (EMAC) complexes consist of a central metal-containing backbone and four specifically designed polydentate ligands. The use of the poly(pyridylamine) ligand with a flexible 1D metal chain developed individually by Cotton and Peng has led to the isolation of metal chains with 3-9 metal atoms. 7 Structurally, the EMAC is possibly the smallest version of an ordinary electrical wire that one can synthesize. In this article, we focus on the conductive properties of the trinuclear compound of the type, [M 3 (µ 3 -dpa) 4 (NCS) 2 ] (M ) Cr, Co, Ni; dpa ) syn-syn-bis(R-pyridyl)amido) (see Figure 1). Experimentally, these mixed-valence stacks of organic as well as inorganic molecules exhibit unusual electrical properties. 8-10 Bond orders for the symmetric and neutral complexes of nickel, cobalt, and chromium are 0, 0.5, and 1.5, which indicate the degree of the electron delocalization and thus the efficiency of the electron transfer through metal centers. 8,11 To calculate the electron-transfer properties, we use the code Hückel IV 3.0, 12 which is based on the nonequilibrium Green's function (NEGF) formalism. The influence of the outside effect (contact) is incorporated into the main body of the device through self-energy matric...

Metal–metal interactions in linear tri-, penta-, hepta-, and nona-nuclear ruthenium string complexes

“…It has been suggested that, in linear metal string complexes, the conductivity and bond order correlate qualitatively [1,27,30]. Following this idea, it can be expected that the conductivity and electron density will also correlate.…”

“…Structures that incorporate one-dimensional metal atom chains attract interest for a variety of reasons, such as their conductivity [1,2], luminescence [3][4][5], vapochromism [6][7][8], and magnetic [9][10][11], and catalytical [12][13][14][15] properties. Some of these properties are linked directly to the interacting metal atoms in the metal chain, while others can be attributed to metal-ligand interactions of single units in the chain.…”

“…Metal string complexes up to a size of nine metal atoms have been synthesized with first row transition metals [28], and up to five metal atoms with second row transition metal atoms [29,30]. Metal string complexes provide a promising approach for the creation of nano-scale electrical wires [1]. The electric conductivity of metal string complexes correlates qualitatively with the strength of the metal-metal interaction in the complex, and can be tuned by the choice of transition metal, its oxidation state, and the ligands used [27].…”

From Homonuclear Metal String Complexes to Heteronuclear Metal String Complexes

“…The four equatorial ligands shield the internal current from outwards flow and become an insulating shroud like that of an electric cable. [61] According to a simple tight-binding calculation, these supporting ligands are considered as nanoscale molecular split-ring resonators (SRRs) and can exhibit simultaneous negative electric permittivity and magnetic permeability in the UV/Vis region. [62] McGrady et al addressed the relationship between the structure and transport phenomena of metal string complexes by analysis of their conduction channels.…”

Syntheses, Characterizations, and Applications of Molecular Metal Wires

“…Measurements were made of the neat solvent under similar conditions to estimate the amplitude and temporal width of XPM occurring through a nonlinear process. Ni (1) and Ni(4) ions are in the high-spin states (S = 1) and are antiferromagnetically coupled. The one-electron-reduced complexes 1 and 3, however, exhibit a delocalized mixed-valence [Ni 2 ] 3+ unit (S = 3/2), which is antiferromagnetically coupled with the terminal high-spin Ni II ion.…”