Phenalenyls, Cyclopentadienyls, and Other Carbon-Centered Radicals - Stable Radicals: Fundamentals and Applied Aspects of Odd-Electron Compounds - page 93

Lewis acid (GaCl 3 ) conditions. Treatment of the cation with tetrabutylammonium iodide (Bu 4 NI) gives
PCPLY as shiny black hexagonal crystals. This neutral radical possesses a high stability in air, while
perchlophenalenone is formed by reaction with oxygen. The melting point of PCPLY is 160 ◦ C in air with
decomposition and is 248 ◦ C under an argon atmosphere.
Characterization of the electronic structure of PCPLY was facilitated by EPR spectroscopy in solution.
The spectrum in benzene shows fifteen peaks with uniform separation with the hfcc (0.06 mT) attributable
to the 35 Cl and 37 Cl nuclei at the positions. 22

positions
are not observed because they are masked in the spectral line width. The spin density distribution obtained
by the quantum chemical calculation based on the crystal structure is shown in Figure 3.11.
PCPLY is easily reduced to the corresponding anion due to the electron withdrawing effect of nine
chlorine substituents. Cyclic voltammetry measurement of the neutral radical in dichloromethane shows
two reversible redox waves at

α The hfccs attributable to chlorine nuclei on the β

0.08 V (vs SCE), which respectively correspond to the
oxidation and reduction processes forming the cation and anion. Compared to the corresponding redox
potentials of the pristine PLY in acetonitrile observed at

+ 1.14 V and −

0.9 V (vs SCE), 17

+ 0.7 V and − redox potentials

of PCPLY show a great cathodic shift.
Single crystals of PCPLY were obtained by repeated sublimation under high vacuum

10 − 5 Torr). 21,23 This molecule has threefold rotational symmetry and a ruffled structure with
a propeller shape (Figure 3.12). The reason is that the intramolecular Cl-Cl distances at the peri positions

(5 ×

Figure3.11 Spindensitydistributionof PCPLY .

(a) (b) (c) (d)

Figure3.12 (a) Molecular structureof PCPLY with a ruffled structure.(b) Projectionalong the c axis. Two sets
of the three independent stacks are shown. The set on the left shows all six molecular orientations for each of
the three stacks. The set on the right shows only three orientationsfor each stack; the other three are generated
by the c glide operations. (c) Columnar structure of PCPLY . (d) Columnar structure without chlorine atoms.
(a,bReprintedwithpermissionfrom[21].Copyright2001AmericanChemicalSociety.)