Molecular Metals with Widely Tunable Band Filling. Structure/Stoichiometry/Counterion Relationships in the Electrochemistry of a Cofacially Joined Polymeric Phthalocyanine Metal

John G. Gaudiello, Glen E. Kellogg, Stephen M. Tetrick, Tobin J. Marks*

*Corresponding author for this work

Research output: Contribution to journalArticle

40 Scopus citations

Abstract

The oxidative electrochemistry of the cofacially joined phthalocyanine polymer [Si(Pc)O]n to yield molecular metals/conductive polymers of the type {[Si(Pc)OJXy}n is studied by a combination of X-ray diffractometric and spectroscopic techniques. Electrochemical methodology includes controlled-potential coulometry and electrochemical potential spectroscopy (ECPS) applied to rapidly stirred slurries or to microcompactions of the solid polymer. For X- = BF4- in acetonitrile, oxidation (“doping”) of as-polymerized orthorhombic [Si(Pc)O]n to yield tetragonal {[Si(Pc)O](BF4)y}n(y = 0.50) is accompanied by a significant overpotential, minimal tunability in y, and involves a first-order structural phase transformation. Electrochemical undoping occurs smoothly and over a broader potential range (0.90 V) to afford tetragonal [Si(Pc)0]„, which is also accessible by thermally undoping ([Si(Pc)O]I1.1}n. Once in the more open tetragonal structure, both the electrochemical and diffraction data argue that y (hence, conduction band filling) can be homogeneously/continuously tuned between 0.0 and 0.50. This result verifies the crystal structural basis of the polymer electrochemical “break-in” phenomenon. It also represents the first case in which the band filling of a molecular metal is broadly tunable. In tetrahydrofuran, tetragonal [Si(Pc)O]n can also be reversibly n-doped to yield |[N(n-butyl)4]0.09[Si(Pc)O]}n. Oxidative ECPS studies with a number of anions in acetonitrile (PF6~, SbF6~, tosylate, CF3(CF2)nSO3-, n = 0, 3, 7) demonstrate that maximum doping stoichiometries achievable (y, hence band filling) are largely a function of anion size, i.e., packing constraints within the tetragonal {[Si(Pc)O]Xy}n crystal structure. In contrast to these results, ECPS studies of solid Ni(Pc) (monoclinic slipped-stack β phase) reveal a first-order structural transformation to yield tetragonal Ni(Pc)(BF4)y(y =0.48) upon oxidative doping, and a subsequent first-order transformation to another slipped-stack Ni(Pc) structure (monoclinic slipped-stack γ phase) upon undoping. Doping/undoping occurs over a relatively narrow potential range; consequently there is far less tunability in y than in the {[Si(Pc)O]Xy}n materials, and large overpotentials are observed. ECPS studies of [Ge(Pc)O]n reveal irreversible oxidative processes, and polymer decomposition via Ge—O bond cleavage is implicated.

Original languageEnglish (US)
Pages (from-to)5259-5271
Number of pages13
JournalJournal of the American Chemical Society
Volume111
Issue number14
DOIs
StatePublished - Jul 1989

ASJC Scopus subject areas

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

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