STRUCTURE AND SOLID-STATE PROPERTIES OF THE STABLE RING-OXIDIZED CONDUCTOR COPC(ASF6)0.5 - INTERACTION BETWEEN RING PI-ELECTRONS AND COBALTD-ELECTRONS

A conducting crystal of (phthalocyaninato)cobalt hexafluoroarsenate, C oPc(AsF6)0.5 is prepared by an electrochemical method. The crystal bel ongs to a tetragonal system with the P4/mcc space group, the lattice c onstants being a = 14.234(2) angstrom, c = 6.296(2) angstrom, and Z = 2. The infrared and visible spectra and thermopower measurements indic ate that the Pc (macrocyclic ligand) ring is mainly oxidized, in contr ast to the analogous compound CoPcI. Thermopower and magnetic suscepti bility results suggest that CoPc(AsF6)0.5 has a narrow Mott-Hubbard ga p at the Fermi level. The electrical conductivity, having a broad peak (almost-equal-to 100 S cm-1) around room temperature, can be understo od by a narrow-gap-semiconductor model. The optical spectrum is also c onsistent with the large-U model. The optical conductivity sigma(omega ) indicates that the CoPc chain produces one-dimensional pi- and d-ban ds along the conducting axis (c axis). We discuss the large-U property based on the exchange interaction between these pi- and d-electrons.