Cu(pc)I: A Molecular Metal With A One-dimensional Array of Local Moments Embedded In A “Fermi Sea” of Charge Carriers

Abstract

Treatment of (phthalocyaninato)copper(II), Cu(pc), with elemental iodine affords (phthalocyaninato)copper iodide, Cu(pc)I. This material is comprised of metal-over-metal stacks of partially oxidized Cu(pc) groups surrounded by linear chains of If ions. Reflectivity spectra from single crystals of Cu(pc)I exhibit a very sharp plasma edge for light polarized parallel to the stacking direction and four-probe conductivity measurements show a room temperature conductivity of ca. 1 23 1 cm1 along this direction. Together these measurements indicate that Cu(pc)I is the most highly conductive porphyrinic molecular metal studied to date and is among the most conductive molecular crystals known. Crystal data: tetragonal, space group D\h-P4/mcc with a = 13.888 (12) Å, c = 6.390 (8) Å,V = 1232 Å3, and Z = 2. Thermoelectric power and magnetic susceptibility measurements show that the charge carriers of Cu(pc)I are holes in the s/6 filled band comprised of overlapping p-π orbitals from adjacent pc rings. The metal sites in this material retain their paramagnetic Cu2+ oxidation state, and thus Cu(pc)I represents the first example of a one-dimensional array of local moments embedded in a “Fermi sea” of charge carriers. The temperature dependence of the EPR g value for Cu(pc)I demonstrates a strong exchange coupling between the localized Cu2+ moments and the mobile charge carriers. An analysis of the temperature dependence of the EPR line width suggests that this exchange may include terms arising from dynamic and quantum mechanical exchange between local and mobile spins in addition to the dipolar and exchange interactions between neighboring Cu2+ sites that occur either directly or are mediated by the continuum of charge carrier states. © 1987, American Chemical Society. All rights reserved.