We show that one can prepare M(pc)I crystals, M = “H2” and Ni, with remarkably improved charge-transport properties by carefully avoiding impurities in the preparation of the M(pc) precursors. The purest H2(pc) (<60 ppm free-radical impurities) was prepared by a melt method in quartz and Teflon vessels while very pure Ni(pc) (170–250 ppm) could only be obtained by metalation of the pure H2(pc). Template syntheses of Ni(pc) result in impure material and are to be discouraged for applications requiring very pure M(pc) materials. H2(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 σ ∼ (1–2) × 104Ω−1cm−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, which suggests that the behavior exhibited by the best materials prepared are representative for the first time of the limiting, intrinsic charge-transport properties of H2(pc)I and Ni(pc)I. A full structure report for H2(pc)I-1 is presented also. The structure consists of metal-over-metal stacks of partially oxidized H2(pc) groups surrounded by linear chains of triiodide anions. The two H2(pc) molecules within a unit cell are staggered by 40°. H2(pc)I crystallizes with two formula units in the tetragonal space group D4h2− P4/mcc with a = 13.931(2) Å, c = 6.411(1) Å, and V = 1244.2(6) Å3(T = 108 K).
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry