Preparation and Characterization of (Tetrabenzoporphyrinato)Cobalt(II) Iodide, a Ring-Oxidized Molecular Conductor

Kwangkyoung Liou, Timothy P. Newcomb, Michael D. Heagy, Julia A. Thompson, William B. Heuer, Ronald L. Musselman, Claus S. Jacobsen, Brian M. Hoffman, James A. Ibers*

*Corresponding author for this work

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45 Scopus citations

Abstract

Oxidation of (tetrabenzoporphyrinato)cobalt(II), Co(tbp), with iodine affords Co(tbp)I. The structure comprises metal-over-metal columnar stacks of partially (one-third) oxidized Co(tbp) groups surrounded by chains of I3- ions. Co(tbp)I crystallizes in the tetragonal space group D24k-P4/mcc with a = 14.129 (3) A, c = 6.334 (1) A, V = 1249 A3, and Z = 2. In contrast to (phthalocyaninato)cobalt(II) iodide, Co(pc)I, which shows metal oxidation and is a metal-spine conductor, conductivity and thermoelectric power measurements on Co(tbp)I show that oxidation occurs at the macrocycle; the charge carriers are holes in the five-sixths-filled band comprising overlapping p-π orbitals from adjacent tbp rings. Reflectance spectroscopy measurements on single crystals provide an explanation of why the tbp macrocycle is more readily oxidized: the p-π orbitals are higher in energy for Co(tbp)I than for Co(pc)I. Ring oxidation of Co(tbp) leaves one spin on each Co2+ ion. However, Co(tbp)I does not exhibit an EPR signal associated with either the carriers or the Co2+ (S=1/2) ions, and the magnetic susceptibility data yield a Curie constant of 0.039 (emu K)/mol, far less than expected for a linear chain of S = */2 spins. In addition, Co(tbp)I does not have a measurable magnetoconductance, as would be expected from a system with conduction electrons scattered by reorientable local moments. This is in contrast to Cu(pc)I, which also is ring oxidized with the metal ion and carriers forming a spin-coupled system, but which shows both the full Curie constant (C = 0.4 (emu K)/mol) for the Cu2+ (S=1/2) ions and an EPR signal. Thus, spins in the Co2+(dr2 orbitals of a partially oxidized Co(tbp) stack must exhibit antiferromagnetic coupling through direct or carrier-mediated interactions, or most likely both, that is much stronger than in Cu(pc)I.

Original languageEnglish (US)
Pages (from-to)4517-4523
Number of pages7
JournalInorganic chemistry
Volume31
Issue number22
DOIs
StatePublished - Jan 1 1992

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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    Liou, K., Newcomb, T. P., Heagy, M. D., Thompson, J. A., Heuer, W. B., Musselman, R. L., Jacobsen, C. S., Hoffman, B. M., & Ibers, J. A. (1992). Preparation and Characterization of (Tetrabenzoporphyrinato)Cobalt(II) Iodide, a Ring-Oxidized Molecular Conductor. Inorganic chemistry, 31(22), 4517-4523. https://doi.org/10.1021/ic00048a015