Structure and solid-state properties of the stable ring-oxidized conductor CoPc(AsF 6) 0.5: interaction between ring π-electrons and cobalt d-electrons

Abstract

A conducting crystal of (phthalocyaninato)cobalt hexafluoroarsenate, CoPc(AsF 6) 0.5, is prepared by an electrochemical method. The crystal belongs to a tetragonal system with the P4/ mcc space group, the lattice constants being a = 14.234(2) A ̊ , c = 6.296(2) A ̊ , and Z = 2. The infrared and visible spectra and thermopower measurements indicate that the Pc (macrocyclic ligand) ring is mainly oxidized, in contrast to the analogous compound CoPcI. Thermopower and magnetic susceptibility results suggest that CoPc(AsF 6) 0.5 has a narrow Mott-Hubbard gap at the Fermi level. The electrical conductivity, having a broad peak ( ≈ 100 S cm −1) around room temperature, can be understood by a narrow-gap-semiconductor model. The optical spectrum is also consistent with the large-U model. The optical conductivity σ(ω) indicates that the CoPc chain produces one-dimensional π- and d-bands along the conducting axis ( c axis). We discuss the large-U property based on the exchange interaction between these π- and d-electrons.