Ja. Thompson et al., SYNTHESIS OF HIGH-PURITY PHTHALOCYANINES (PC) - HIGH INTRINSIC CONDUCTIVITIES IN THE MOLECULAR CONDUCTORS H2(PC)I AND NI(PC)I, Inorganic chemistry, 32(16), 1993, pp. 3546-3553
We show that one can prepare M(pc)I crystals, M = ''H-2'' and Ni, with
remarkably improved charge-transport properties by carefully avoiding
impurities in the preparation of the M(pc) precursors. The purest H-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 ppm) coul
d only be obtained by metalation of the pure H-2(pc). Template synthes
es of Ni(pc) result in impure material and are to be discouraged for a
pplications requiring very pure M(pc) materials. H-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 temp
erature the conductivities exhibit maximum values that are ca. 30-fold
greater than at room temperature, not 5-7-fold as seen before, with a
bsolute values of sigma approximately (1-2) x 10(4) OMEGA-1 cm-1. The
study of a series of Ni(pc)I compounds prepared from Ni(pc) parent mat
erials exhibiting a range of purity levels further shows a strong corr
elation between the charge-transport properties and the level of param
agnetic impurities in the macrocycle precursor. However, the maximum c
onductivity appears to saturate at the lowest impurity concentrations,
which suggests that the behavior exhibited by the best materials prep
ared are representative for the first time of the limiting, intrinsic
charge-transport properties of H-2(pc)I and Ni(pc)I. A full structure
report for H-2(pc)I-1 is presented also. The structure consists of met
al-over-metal stacks of partially oxidized H-2(pc) groups surrounded b
y linear chains of triiodide anions. The two H-2(pc) molecules within
a unit cell are staggered by 40-degrees. H-2(pc)I crystallizes with tw
o formula units in the tetragonal space group D4h2 - P4/mcc with a = 1
3.931(2) angstrom, c = 6.411(1) angstrom, and V = 1244.2(6) angstrom3
(T = 108 K).