Synthesis of high-purity phthalocyanines (pc): high intrinsic conductivities in the molecular conductors H2(pc)I and Ni(pc)I

Abstract

The authors show that one can prepare M(pc)I crystals, M = [open quotes]H[sub 2][close quotes] and Ni, with remarkably improved charge-transport properties by carefully avoiding impurities in the preparation of the M(pc) precursors. The purest H[sub 2](pc) (<60 ppm free-radical impurities) was prepared by a melt method in quartz and Teflon vessels while very pure Ni(pc) (170-250 pm) could only be obtained by metalation of the pure H[sub 2](pc). Template syntheses of Ni(pc) result in impure material and are to be discouraged for applications requiring very pure M(pc) materials. H[sub 2](pc)I and Ni(pc)I synthesized from the high-purity precursors remain metallic down to ca. 3 K, a far lower temperature than ever before observed. At this temperature the conductivities exhibit maximum values that are ca. 30-fold greater than at room temperature, not 5-7-fold as seen before, with absolute values of [sigma] [approximately] (1-2) [times] 10[sup 4] [Omega][sup [minus]1] cm[sup [minus]1]. The study of a series of Ni(pc)I compounds prepared from Ni(pc) parent materials exhibiting a range of purity levels further shows a strong correlation between the charge-transport properties and the level of paramagnetic impurities in the macrocycle precursor. However, the maximum conductivity appears to saturate at the lowest impurity concentrations, whichmore » suggests that the behavior exhibited by the best materials prepared are representative for the first time of the limiting, intrinsic charge-transport properties of H[sub 2](pc)I and Ni(pc)I. A full structure report for H[sub 2](pc)I-1 is presented also. The structure consists of metal-over-metal stacks of partially oxidized H[sub 2](pc) groups surrounded by linear chains of triiodide anions. H[sub 2](pc)I crystallizes with two formula units in the tetragonal space group D[sub 4h][sup 2]-P4/mcc with a = 13.931 [angstrom], c = 6.411 [angstrom], and V = 1244.2 [angstrom][sup 3] (T = 108 K).« less