Molecular Metals with Widely Tunable Band Filling. Response of the Collective Properties of a Phthalocyanine Molecular Metal to Drastic Excursions in Partial Oxidation State and Charge-Compensating Counterions

Manuel Almeida, John G. Gaudiello, Glen E. Kellogg, Stephen M. Tetrick, Tobin J. Marks, Henry O. Marcy, William J. McCarthy, John C. Butler, Carl R. Kannewurf

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Abstract

The electrical, optical. and magnetic properties of the partially oxidized, cofacially joined phthalocyanine polymers {[Si(Pc)O]Xy}n are investigated for X- = BF4-, y = 0.00-0.50; X- = p-toluenesulfonate (TOS-), y = 0.00-0.67; and X- = SO42-, y = 0.040, 0.095. As a function of increasing y, the physical properties of the BF4- and TOS salts evidence a transition at y ≈ 0.20 from a localized carrier semiconductor or insulator to a molecular metal. Thus, the dc electrical conductivity increases from low values having a temperature dependence most characteristic of disorder and/or hopping transport between localized states to values characteristic of a molecular metal with fluctuation-induced carrier tunneling between relatively large metallike particles. Beyond y ≳ 0.25, the conductivity is only weakly dependent on y. At y ≈ 0.20, the thermoelectric power [S(T)] also changes from behavior characteristic of a p-type semiconductor or insulator to that of a p-type molecular metal. Differences in S(T) between X- = BF4- and TOS polymers appear to be due largely to minor structural variations. Optical reflectivity measurements reveal the appearance of a metallike plasma edge at y 0.20, followed by an incremental shift of this feature to higher energy with further increase in y. The static magnetic susceptibility of {[Si(Pc)O](BF4)y}n evidences an abrupt transition at y ≈ 0.20 from a large concentration of localized, Curie-like spins to Pauli-like behavior characteristic of a molecular metal. Beyond y ≳ 0.30, the Pauli-like susceptibility is nearly independent of y. ESR studies indicate a ligand-centered π-radical-cation electronic structure. For X- = BF4- and TOS-, line-width studies as a function of y evidence a progression from relatively localized to delocalized carriers. It is suggested that the insulator/semiconductor to molecular metal transition in these materials is an Anderson-like transition that arises when the Fermi level crosses a mobility edge from localized states (presumably due to disorder and/or defects) at the tail of the conduction band to delocalized, metallike states. With the possible exception of ESR line-width data, the electrical, optical, and magnetic studies of {[Si(Pc)O] (SO4)0.095}n provide no evidence for an enhanced, carrier-localizing perturbation of the [Si(Pcρ+)O]n band structure by the dinegative off-axis counterions.

Original languageEnglish
Pages (from-to)5271-5284
Number of pages14
JournalJournal of the American Chemical Society
Volume111
Issue number14
DOIs
Publication statusPublished - Jul 1989

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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