Odd Electron Chains

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Science  17 Oct 2008:
Vol. 322, Issue 5900, pp. 348
DOI: 10.1126/science.322.5900.348b

Organic materials that contain linear chains of metals in different valence states can behave as semiconductors or even exhibit metallic conductivity. Mitsumi et al. have explored a strategy for creating mixed-valence platinum (Pt) compounds by electrochemically oxidizing Pt(II) dimer precursors in organic solvents with noncoordinating ClO4 counterions. These dimers are stabilized by bridging dithiocarboxylato ligands (RCS2-where R is an alkyl group), and, in the mixed-valence form, the Coulomb barrier that limits conductivity should be reduced by the presence of a shared unpaired electron in the Pt-Pt bonds and delocalized orbitals on the S atoms. For both methyl and ethyl analogs, the Pt dimers form linear chains with a mix of Pt2+ and Pt3+ centers (average oxidation states of 2.125 and 2.2, respectively). Crystal structures reveal that in the methyl analog, the chains arrange in parallel stacks separated by layers of solvent and ClO4 counterions. This compound, with one unpaired electron per chain repeat, exhibits high metallic conductivity at room temperature that persists to about 125 K (between 4 and 8 Siemens per cm). In the ethyl analog, in contrast, each chain is surrounded by solvent and counterions, and a longer repeat unit leads to pairing of the odd electrons and semiconducting behavior. — PDS

J. Am. Chem. Soc. 130, 10.1021/ja805794a (2008).

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