Electron Self-Exchange Dynamics of an Iron Bipyridine Complex Redox Polyether Hybrid in Its Room Temperature Melt

Abstract

The derivatization of metal-tris(2,2′-bipyridine) complexes with oligo(ethylene glycol) tails produces ionicallyconductive room-temperature melts in which appreciable concentrations of lithium electrolytes dissolve. Charge transport rates in these redox polyether hybrids, in the undiluted state, have been investigated using microelectrode solid state voltammetry. In the ligand bpy(CO 2 MPEG350) 2 , MPEG350 is -(CH 2 CH 2 O) 7 -CH 3 . The apparent diffusion coefficient, D APP , for the oxidation of [Fe(bpy(CO 2 MPEG350) 2 ) 3 ](ClO 4 ) 2 is ca. 10 3 larger than that for [Co(bpy(CO 2 MPEG350) 2 ) 3 ](ClO 4 ) 2 . This difference is ascribed to transport dominated in the former by electron self-exchange reactions between adjacent Fe(II) and Fe(III) complexes. The very slow physical self-diffusivity in these metal complex melts, measured by the Co(III/II) reaction, provides an opportunity to assess the effect of electron donor/acceptor concentration on electron self-exchange dynamics in a semisolid matrix. Various models have been described for the site concentration dependency of charge transport in redox polymers, including ion association, electron migration, and percolation. This study examines the effects of changing redox site concentration on D APP by diluting [Fe(bpy(CO 2 MPEG350) 2 ) 3 ](ClO 4 ) 2 isostructurally with the analogous Co and Ni complexes, and interprets the results in the context of the previous models.

Interpretation of electron diffusion coefficient in organic and inorganic semiconductors with broad distributions of states

“…12,13,19,139 The effect of percolation features prominently in the electron transport through redox centers in a solid matrix where the center concentration can be readily varied. 7,36,[140][141][142] However, in these systems the redox centers undergo displacement to a certain extent, from bounded motion around fixed positions, to long range diffusion. The electron transport is a combination of redox center mobility and electron hopping between centers.…”

Development of Electrochemical Analyzer for Polymer-Coated Electrode

“…Whereas in a polymer matrix, the electrons are transferred not only by the physical diffusion but also electron hopping because the physical diffusion is suppressed in the polymer matrix. In such a case, when a material exists in a polymer matrix homogeneously, the molar flux of the electrons is proportional to the concentration gradient [13,14] …”

“…Since many studies have been done on electrodes modified with these complexes [4][5][6][7][8][9][10][11][12][13][14][15][16], these electrodes have come to be applied in chemical sensors [4], electrocatalysis [5,6], and fuel cell power systems. These electrodes have a potential to develop new devices because of many combinations of a polymer matrix and a functional complex.…”

Electrocatalysis in Nucleic Acid Molten Salts

“…In this paper, electron-transfer reactions of DNA are observed in an electrocatalytic scheme where PEG-tailed metal bipyridine complexes Fe(bpy 350 ) 3 (ClO 4 ) 2 and Ru(bpy 350 ) 3 (ClO 4 ) 2 (M 350 ) are added to Co(bpy 350 ) 3 DNA melts. The strongly oxidizing M 3+ states of the Fe and Ru complexes are electrochemically generated (with heterogeneous electron-transfer rate constants k°, eq 1) and react with DNA base sites (Scheme 1, guanine and adenine, with rate constants k 1 , eq 2) according to the electrocatalytic scheme…”