Synthesis, isolation, and structural characterization of the C4h isomer of metal(1,2-naphthalocyanine) and its one-dimensional conductor of the axially substituted species

Article abstract of DOI:10.1021/ic0520622

The C_4h isomer of the 1,2-Nc (1,2-naphthalocyaninato) ligand has been efficiently isolated as a hydrated magnesium complex by the fractional crystallization from the benzene/acetone solution after treating the crude mixture of the four isomers (C_4h, C_s, C_2v, D_2h) with benzene. The C_4h symmetry has been confirmed by X-ray structure analysis. The central metal ion has been demetalated and subsequently converted to the Li₂ complex followed by conversion to the cobalt(II) complex. Electrochemical oxidation of the Co^III(1,2- Nc)(CN)₂ anion prepared from the cobalt(II) complex with TPP (tetraphenylphosphonium) has yielded a partially oxidized salt, TPP[Co ^III(1,2-Nc-C_4h)(CN)₂]₂. The crystal comprises slipped stacked Co^III(1,2-Nc-C_4h)(CN) ₂ one-dimensional chains and one-dimensional arrays of TPPs. The conductivity at room temperature is 0.1 S cm^-1, and the temperature dependence is semiconducting with a small activation energy of about 0.05 eV. The positive temperature-independent value of about 60 μV deg^-1 observed in the thermoelectric power measurements suggests that the salt is in the correlated hopping regime.

Full text of DOI:10.1021/ic0520622

Inorg. Chem. 2006, 45, 4170−4176
Synthesis, Isolation, and Structural Characterization of the C4h Isomer
of Metal(1,2-naphthalocyanine) and Its One-Dimensional Conductor of
the Axially Substituted Species
Eduardo H. Gacho,† Hiroyuki Imai,† Ryo Tsunashima,† Toshio Naito,† Tamotsu Inabe,*,† and
Nagao Kobayashi‡
DiVision of Chemistry, Graduate School of Science, Hokkaido UniVersity,
Sapporo 060-0810, Japan, and Department of Chemistry, Graduate School of Science,
Tohoku UniVersity, Sendai 980-8578, Japan
Received December 1, 2005
The C4h isomer of the 1,2-Nc (1,2-naphthalocyaninato) ligand has been efficiently isolated as a hydrated magnesium
complex by the fractional crystallization from the benzene/acetone solution after treating the crude mixture of the
four isomers (C4h, Cs, C2v, D2h) with benzene. The C4h symmetry has been confirmed by X-ray structure analysis.
The central metal ion has been demetalated and subsequently converted to the Li2 complex followed by conversion
to the cobalt(II) complex. Electrochemical oxidation of the CoIII(1,2-Nc)(CN)2 anion prepared from the cobalt(II)
complex with TPP (tetraphenylphosphonium) has yielded a partially oxidized salt, TPP[CoIII(1,2-Nc-C4h)(CN)2]2.
The crystal comprises slipped stacked CoIII(1,2-Nc-C4h)(CN)2 one-dimensional chains and one-dimensional arrays
of TPPs. The conductivity at room temperature is 0.1 S cm-1, and the temperature dependence is semiconducting
1
with a small activation energy of about 0.05 eV. The positive temperature-independent value of about 60
observed in the thermoelectric power measurements suggests that the salt is in the correlated hopping regime.
µ
V deg-
Introduction
of the π-ligand yields 2,3-naphthalocyanine (2,3-Nc) deriva-
tives, and CoIII(2,3-Nc)(CN)2 has been found to give
conducting neutral radical crystals.15,16 Compared with the
linear extension, angular extension of the π-ligand is much
more complicated; the conventional synthetic route produces
four isomers (C4h, Cs, C2V, D2h: Scheme 1) simultaneously;
however, isolation is rather difficult. Among them, the C4h
isomer is expected to maintain the planar structure and to
give a uniform and efficient π-π stacking interaction when
Phthalocyanines have been known as a functional dye, and
their semiconducting electrical properties were noted in as
early as 1948.1 As organic conductors were developed,
phthalocyanines have been utilized as a component of
molecular2 and axially bridged polymeric3,4 conductors with
one-dimensional columnar structure and neutral radical
conductors.5 Besides them, axially substituted phthalo-
cyanines, M(Pc)(CN)2; where M ) CoIII and FeIII, Pc )
phthalocyaninato, were also found to be a promising
component of molecular conductors.6-14 The linear extension
(8) Hasegawa, H.; Naito, T.; Inabe, T.; Akutagawa, T.; Nakamura, T. J.
Mater. Chem. 1998, 8, 1567.
(9) Takano, S.; Naito, T.; Inabe, T. Chem. Lett. 1998, 1249.
(10) Fujita, A.; Hasegawa, H.; Naito, T.; Inabe, T. J. Porphyrins Phtha-
locyanines 1999, 3, 720.
(11) Matsuda, M.; Naito, T.; Inabe, T.; Hanasaki, N.; Tajima, H.; Otsuka,
T.; Awaga, K.; Narymbetov, B.; Kobayashi, H. J. Mater. Chem. 2000,
10, 631.
(12) Matsuda, M.; Naito, T.; Inabe, T.; Hanasaki, N.; Tajima, H. J. Mater.
Chem. 2001, 11, 2493.
(13) Asari, T.; Naito, T.; Inabe, T.; Matsuda, M.; Tajima, H. Chem. Lett.
2004, 33, 128.
* To whom correspondence should be addressed.
† Hokkaido University.
‡ Tohoku University.
(1) Eley, D. D. Nature 1948, 162, 819.
(2) Inabe, T.; Tajima H. Chem. ReV. 2004, 104, 5503, and references
therein.
(3) Marks, T. J. Angew. Chem., Int. Ed. Engl. 1990, 29, 857.
(4) Hanack, M.; Datz, A.; Fay, R.; Fischer, K.; Keppeler, U.; Koch, J.;
Metz, J. Mezger, M.; Schneider, O.; Schulze, H.-J. Handbook of
Conducting Polymers; Skotheim, T. A., Ed.; Marcel Dekker: New
York, 1986.
(14) Asari, T.; Ishikawa, M.; Naito, T.; Matsuda, M.; Tajima, H.; Inabe,
T. Chem. Lett. 2005, 34, 936.
(5) Turek, P.; Petit, P.; Andore, J. J.; Simon, J.; Even, R.; Boudjema, B.;
Guillaud, G.; Maitrot, M. J. Am. Chem. Soc. 1987, 109, 5119.
(6) Inabe, T. J. Porphyrins Phthalocyanines 2001, 5, 3.
(7) Morimoto, K.; Inabe, T. J. Mater. Chem. 1995, 5, 1749.
(15) Matsumura, N.; Fujita, A.; Naito, T.; Inabe, T. J. Mater. Chem. 2000,
10, 2266.
(16) Naito, T.; Matsumura, N.; Inabe, T.; Matsuda, M.; Tajima, H. J.
Porphyrins Phthalocyanines 2004, 8, 1258.
4170 Inorganic Chemistry, Vol. 45, No. 10, 2006
10.1021/ic0520622 CCC: $33.50
© 2006 American Chemical Society
Published on Web 04/12/2006

C4h Isomer of Metal(1,2-naphthalocyanine)
Scheme 1
Experimental Section
Preparation of Mg(1,2-Nc-C4h)H2O. A solid mixture of the
Mg(1,2-Nc) isomers was prepared as previously described.18,19 1,2-
Naphthalenedicarbonitrile (4.93 g, 0.0276 mol) was heated with
excess Mg metal in a N2 atmosphere at 375 °C for 2 h. The reaction
mixture was cooled to room temperature then heated to around 200
°C under vacuum for 1 h to remove the majority of unreacted 1,2-
naphthalenedicarbonitrile. After cooling to room temperature, the
remaining solid was finely ground and washed with methylcyclo-
hexane using a Soxhlet extractor for 24 h, and the remaining powder
was dried under vacuum. The powder was subsequently stirred in
water/ethanol (1:5 in volume) for 2 h. After being filtered and dryed
under vacuum, the solid was subjected to extraction with benzene
(200 mL) using a Soxhlet extractor for 24 h. Acetone (20 mL) was
added to the resultant benzene solution at room temperature, and
the dark green solution was left to stand. Purple prism crystals were
collected after about 1 week. Addition of a small amount of acetone
to the filtrate gave further precipitation of the desired product. The
composition of the crystal was determined to be Mg(1,2-Nc-C4h)-
H2O‚(acetone)‚3(benzene) on the basis of X-ray structure analysis.
Total yield; 0.735 g (17%).
Preparation of H2(1,2-Nc-C4h). The Mg complex obtained was
dissolved in concentrated H2SO4 and poured through a glass frit
onto the crushed ice. The green precipitate identified as H2(1,2-
Nc-C4h) by IR spectra was filtered and washed with hot water,
methanol, acetone, and ether. Quantitative yield (g95%).
it forms the crystalline conductors by oxidation of the
π-ligand.
Preparation of CoII(1,2-Nc-C4h). A solution of butyllithium
(1.59 mmol) was added dropwise to a suspension of H2(1,2-Nc-
C4h) (0.400 g, 0.56 mmol) in 15 mL of dehydrated DMSO under
a N2 atmosphere. The suspension was then heated to 180 °C and
stirred for 30 min. A solution of Co(OAc)2 (1.3 mmol) in DMSO
was then added dropwise to the suspension and stirred for 1 h more
at 180 °C. After the mixture cooled, distilled water was added
slowly. The precipitate was filtered and washed extensively with
water, ethanol, and acetone. The solids were then stirred in
concentrated H2SO4 and poured through a glass frit onto the crushed
ice. The precipitate was filtered, washed, and dried. No trace of
the H2 complex was observed in the IR spectra. Yield; 0.39 g (90%).
There have been a few reports on the synthesis and
isolation of 1,2-Nc’s. While 1,2-Nc’s lacking peripheral
substituents are generally insoluble, the first successful
separation was reported for the C4h isomer of Fe(1,2-Nc)-
(isocyanocyclohexyl)2, which was relatively soluble upon
complexation with the axial ligand.17 Recently, Simon et al.
reported that each of the four isomers of the magnesium
complex can be isolated.18 The magnesium complexes were
relatively soluble in common organic solvents,19 which
enabled isolation by column chromatography; however, it
was extremely time-consuming and required excessive
amount of solvent to elute the purified complexes. In the
current work, the C4h magnesium isomer has been isolated
from the crude mixture by fractional crystallization. This
method has proven to be remarkably efficient for the C4h
isomer. The successful isolation of a preparative amount of
the C4h magnesium isomer allowed us to prepare the metal-
free species and achieve further metal insertion into this
ligand. Thus, the axially substituted compound, (cation)[CoIII-
(1,2-Nc-C4h)(CN)2], has been obtained from the cobalt(II)
complex. Electrochemical oxidation of [CoIII(1,2-Nc-C4h)-
(CN)2]- with tetraphenylphosphonium (TPP) has yielded a
conducting partially oxidized salt, TPP[CoIII(1,2-Nc-C4h)-
(CN)2]2, which is analogous to the Pc system, TPP[CoIII-
(Pc)(CN)2]2. In this paper, preparation, isolation, and struc-
tural and optical characterization of the metal complexes of
1,2-Nc-C4h and physical properties of TPP[CoIII(1,2-Nc-C4h)-
(CN)2]2 are presented and compared with the corresponding
Pc species.
Preparation of K[CoIII(1,2-Nc-C4h)(CN)2]. A suspension of CoII-
(1,2-Nc-C4h)(0.21 g, 0.27 mmol) and KCN (0.40 g, 6.14 mmol) in
ethanol (50 mL) was stirred at 60 °C for 72 h (open to the air).
Water was then added to the suspension, and the precipitate was
filtered and washed with water. K[CoIII(1,2-Nc-C4h)(CN)2] was
extracted with dry acetone using a Soxhlet extractor. The extracted
solution was reduced to one-fifth of the volume and diluted with
1
hexane. The precipitated solids were filtered and dried. H NMR
spectra confirmed that the product contained a single conformer
(Supporting Information). Yield; 0.10 g (43%).
Preparation of Et4N[CoIII(1,2-Nc-C4h)(CN)2]. A suspension of
CoII(1,2-Nc-C4h)(0.2 g, 0.26 mmol) and tetraethylammonium
cyanide (0.5 g, 3.2 mmol) in dry ethanol (50 mL) was refluxed for
72 h with a CaCl2 tube. The precipitate was filtered and washed
with water. Et4N[CoIII(Pc)(CN)2] was extracted with dry acetonitrile
using a Soxhlet extractor. The extracted solution was reduced to
one-fifth of the volume and diluted with hexane. The precipitated
solids were filtered and dried. Yield; 0.10 g (40%).
Preparation of TPP[CoIII(1,2-Nc-C4h)(CN)2]2. An electrochemi-
cal cell with a glass frit was filled with an acetonitrile solution
containing [CoIII(1,2-Nc-C4h)(CN)2]- (0.4 mmol dm-3) and TPP‚
Br (0.4 mmol dm-3). The solution was left to stand for 12 h at 20
°C without current flow to achieve the equilibrium conditions (some
precipitation of the cation exchanged species occurs). A constant
(17) Hanack, M.; Renz, G.; Stra¨hle, J.; Schmid, S. Chem. Ber. 1988, 121,
1479.
(18) Negrimovskii, V. M.; Bouvet, M.; Luk’yanets, E. A.; Simon, J. J.
Porphyrins Phthalocyanines 2000, 4, 248.
(19) Bradrook, E. F.; Linstead, R. P. J. Chem. Soc. 1936, 1739.
Inorganic Chemistry, Vol. 45, No. 10, 2006 4171

Gacho et al.
Table 1. Data-Collection Conditions and Crystal Data for
Mg(1,2-Nc-C4h)H2O‚(acetone)‚3(benzene) and
TPP[Co(1,2-Nc-C4h)(CN)2]2
between the crystal and gold lead wires (diameter ) 20 µm) were
made by a gold paste, and the ohmic behavior was confirmed in
the range of the applied current of 1-10 µA. The thermoelectric
power measurement was carried out using a system similar to that
previously reported.23 Two heater blocks were separated by 1 mm,
and the thermal and electrical contacts between the heater blocks
and the sample crystal were made with gold foils (thickness ) 1
µm) and a gold paste. The temperature gradient was maintained
less than 0.5 °C for the whole temperature range. The emf of the
system was calibrated by a standard sample of constantan wire,
and the reproducibility was checked for several different crystals.
Mg(1,2-Nc-C4h)H2O‚
TPP[Co-
compound
(acetone)‚3(benzene) (1,2-Nc-C4h)(CN)2]2
Crystal Data
formula
fw
cryst syst
C69H50N8MgO2
1047.51
monoclinic
P21/n
C124H68N20Co2P
1986.88
tetragonal
I41/a
space group
a/Å
b/Å
c/Å
18.172(1)
12.780(1)
22.961(1)
93.29(1)
5323.9(4)
4
32.511(1)
32.511(1)
8.662(1)
90
9155.4(5)
4
â/°
V/Å3
Results and Discussion
Z
Dx/g cm-3
1.307
0.91
1.441
4.50
Synthesis and Isolation. The fractional crystallization of
the isomer mixture obtained from a direct reaction between
1,2-naphthalenedicarbonitril and Co2(CO)8 was found to be
successful for the isolation of the C2V isomer but not for the
C4h isomer.24 Since the cobalt(II) complex is not satisfactorily
soluble, isolation of the C4h isomer is rather difficult, even
upon attachment of axial ligands. Bradbrook and Linstead
reported that the magnesium complex is relatively soluble
in common solvents.19 Therefore, the target was changed to
this complex, and the central metal was intended to be
exchanged after the isolation according to the report by
Simon et al.18 Extraction of the pure single isomer from the
mixture merely by the solubility difference was not success-
ful, whereas the benzene extraction of the hydrated com-
pound gave a C4h-rich solution. Furthermore, preferential
crystallization of the C4h isomer occurred when a small
amount of acetone was added to the C4h-rich benzene
solution. Upon treatment of the mixture of the four isomers
with water/ethanol, the hydration reaction was assumed to
go to completion for all the isomers. Asymmetric water
coordination to the planar isomers leads to symmetry
reduction due to the loss of one plane of symmetry. The
isomer with C2V or D2h symmetry maintains another plane
of symmetry, and no racemization occurs. High symmetries
are thought to be advantageous for fractional crystallization;
however, no crystalline products have been obtained for the
Mg isomers. This may be attributed to the small content of
these isomers.18 Indeed, when the content of the C2V isomer
was rich, the asymmetrically pyridine-coordinated C2V species
was preferentially isolated for the CoII complex in the
crystalline form.24
µ(Mo KR)/cm-1
Data Collection
54.98
113
2θmax/°
Temp of data collection/K
no. of reflns
total
unique (Rint
54.96
123
45 423
11 984 (0.053)
37 533
5242 (0.101)
)
Refinement
721
0.062
0.142
1.107
no. of variables
R1 [I > 2.0σ(I)]
wR2 (F2, all data)
GOF
333
0.066
0.119
0.822
current of 0.5 µA was applied to two platinum electrodes immersed
in the solution in each compartment for 6 days at 20 °C. Needlelike
crystals grew on the anode surface as the current flowed. Some
unidentified solid products were also deposited on the electrode
surface. They were largely noncrystalline and probably byproducts
of electrochemical oxidation of [CoIII(1,2-Nc-C4h)(CN)2]-. Only the
crystalline needles were harvested by filtration. The composition
of TPP[CoIII(1,2-Nc-C4h)(CN)2]2 was confirmed by X-ray structural
analysis. More than 10 crystals were subjected to the diffraction
experiments, and all of them were found to have the same unit cell
parameters.
X-ray Structure Analyses. Single-crystal X-ray diffraction
measurements using an automated Rigaku R-axis RAPID imaging
plate diffractometer with graphite-monochromated Mo KR radiation
were performed for the two crystals; Mg(1,2-Nc-C4h)H2O‚(acetone)‚
3(benzene) and TPP[CoIII(1,2-Nc-C4h)(CN)2]2. All of the measure-
ments were carried out at a low temperature using cold nitrogen
gas flow equipment. The crystal data are summarized in Table 1.
The structures were solved by direct methods (SIR-88,20 SIR-9221),
and the hydrogen atoms were placed at the calculated ideal
positions. A full-matrix least-squares technique with anisotropic
thermal parameters for non-hydrogen atoms and isotropic param-
eters (1.2× of the attached atom) for hydrogen atoms was employed
for structural refinement using the teXsan program package.22
Measurements. UV-vis spectra were measured for the pyridine
solutions on a JASCO Ubest V570 spectrometer. IR spectra for
the KBr disk specimen were recorded on a Perkin-Elmer 1600 FTIR
Hydration of the C4h and Cs isomers, which are the major
isomers in Mg(1,2-Nc),18 leads to racemization, and the point
groups change to C4 and C1, respectively. The higher
symmetry of the former is advantageous in crystallization
compared with the irregular shape of the latter. As will be
described later, the hydrated magnesium 1,2-Nc-C4h complex
crystallizes with benzene and acetone. The benzene mol-
ecules can be displaced by pyridine, and the space-filling
feature of these solvents seems to be a key in the successful
isolation of the C4h isomer by simple fractional crystalliza-
tion.
1
spectrometer. H NMR measurements for the DMSO-d6 solutions
were performed using a 400 MHz JEOL NMR spectrometer.
Electrical conductivity was measured in the temperature range of
85-300 K using a standard four-probe method. The contacts
(20) Burla, M. C.; Camalli, M.; Cascarano, M.; Giacovazzo, M.; Polidori,
C.; Spagna, R.; Viterbo, D. J. Appl. Cryst. 1989, 22, 389.
(21) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.; Giacovazzo,
M.; Guagliardi, A.; Polidori, C. J. Appl. Cryst. 1994, 27, 435.
(22) TeXsan, Crystal Structure Analysis Package; Molecular Structure
Corporation: The Woodlands, TX, 1985 and 1992.
(23) Chaikin, P. M.; Kwak, J. F. ReV. Sci. Instrum. 1975, 46, 429.
(24) Gacho, H. G.; Naito, T.; Inabe, T.; Fukuda, T.; Kobayashi, N. Chem.
Lett. 2001, 260.
4172 Inorganic Chemistry, Vol. 45, No. 10, 2006

C4h Isomer of Metal(1,2-naphthalocyanine)
Figure 2. ORTEP drawing of the Mg(1,2-Nc-C4h)H2O unit.
Table 2. Bond Lengths in the 1,2-Nc-C4h Ligand (Å, Averaged by the
C4h Symmetry) and in the Pc Ligand (Å, Averaged by the D4h
Symmetry)a
Figure 1. Infrared spectra of (a) Mg(1,2-Nc-C4h)H2O, (b) H2(1,2-Nc-C4h),
(c) CoII(1,2-Nc-C4h), and (d) K[CoIII(1,2-Nc-C4h)(CN)2]. Arrows in (b)
indicate characteristic peaks.
The C4h symmetry of the isolated isomer has been
confirmed by X-ray analysis; therefore, further chemical
modifications were rather straightforward. After demetalation
using a conventional method, several methods were under-
taken in an effort to convert the isomer to the cobalt(II)
complex. Refluxing H2(1,2-Nc-C4h) with CoCl2 in quinoline,
1-chloronaphthalene, or DMSO and with Co2(CO)8 in
ethylene glycol did not give a satisfactory yield. The best
result was obtained when the metalation was performed with
the Li2 complex following a literature procedure.18
The IR spectra of the isolated chemical species are shown
in Figure 1. The demetalation from Mg to H2, as well as
metalation from H2 to Co, was followed by a dramatic change
in the spectra. The characteristic peaks of H2(1,2-Nc-C4h) at
921 and 678 cm-1 (indicated by arrows in Figure 1b) may
be associated with the N-H out-of-plane deformation and
in-plane deformation, respectively. These peaks are observed
at 999 and 715 cm-1 in H2(Pc).25 Two peaks in the region
of 1000-1050 cm-1 also show characteristic variations by
the central chemical species. These features were also utilized
to monitor the reaction.
Structure of Mg(1,2-Nc-C4h)H2O‚(acetone)‚3(benzene).
The molecular structure is shown in Figure 2. In this crystal,
a Mg(1,2-Nc-C4h)H2O unit is crystallographically indepen-
dent. As described above, the 1,2-Nc-C4h unit is now a
racemic body and the two enantiomers are related by a center
of inversion. The Nc ligand is practically planar and the
central Mg atom is slightly deviated from the ligand plane
(0.497 Å). The bond lengths for the Nc ligand are sum-
marized in Table 2. Compared with the nearly D4h symmetry
of the tetraazaporphyrin (TAz) framework in Mg(Pc)H2O,26
as indicated by relatively small differences in averaging, C4h-
type deformation of the TAz framework in the Mg(1,2-Nc-
C4h)H2O unit is detectable: bond e is shortened and bond f
is lengthened. This deformation was also observed for Fe-
[CoIII(1,2-Nc-
bond
Mg(Pc)H2Ob
Mg(1,2-Nc-C4h)H2O
C4h)(CN)2]0.5-
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
1.336(7)
1.367(12)
1.367(12) ()b)
1.336(7) ()a)
1.456(5)
1.456(5) ()e)
1.394(6)
1.391(6)
1.391(6) ()h)
1.377(6)
1.377(6) ()j)
1.394(6)
-
-
-
-
-
1.335(8)
1.386(8)
1.363(6)
1.339(5)
1.437(10)
1.463(4)
1.409(12)
1.414(11)
1.412(11)
1.360(7)
1.420(4)
1.415(4)
1.438(6)
1.359(4)
1.414(5)
1.353(6)
1.426(6)
1.316(12)
1.496(17)
1.323(14)
1.310(9)
1.357(9)
1.429(28)
1.474(9)
1.526(20)
1.385(15)
1.378(15)
1.40(3)
1.36(2)
1.45(3)
1.31(3)
1.54(1)
1.32(2)
1.42(1)
a The values in parentheses are the maximum difference from the average
value or the maximum standard deviation. b Reference 26.
(1,2-Nc)(isocyanocyclohexyl)2.17 The peripheral naphthalene
ring maintains the characteristics observed for naphthalene:
27 relatively short bond lengths for n, p, and j. Bond g, which
is also short in naphthalene, is not as short because the bond
is shared with the TAz ring.
A portion of the crystal packing is shown in Figure 3.
Hydrogen bonds between the axial H2O and acetone (O‚‚‚O
distances; 2.803(2) and 2.810(2) Å) bridge the two Nc units.
Six benzene molecules are packed between the two Nc
planes, so that the void between the planes is effectively
filled. Therefore, two units of crystallographically indepen-
dent Mg(1,2-Nc-C4h)H2O‚(acetone)‚3(benzene), related by a
center of inversion, form a relatively condense structural unit
that can efficiently crystallize.
(25) Kobayashi, T.; Kurokawa, F.; Uyeda, N.; Suito, E. Spectrochim. Acta
1970, 26A, 1305.
(26) Fischer, M. S.; Templeton, D. H.; Zalkin, A.; Calvin, M., J. Am. Chem.
Soc. 1971, 93, 2622.
(27) Brock, C. P.; Dunitz, J. D. Acta Crystallogr., Sect. B 1982, 38, 2218.
Inorganic Chemistry, Vol. 45, No. 10, 2006 4173

Gacho et al.
Electrochemical Oxidation of [Co(1,2-Nc-C4h)(CN)2]-.
The cyclic voltammetry of K[Co(1,2-Nc-C4h)(CN)2] in DMF
showed the first oxidation process at 1.02 V vs Ag/Ag+. This
oxidation corresponds to the π-ligand oxidation observed at
0.96 V for K[Co(Pc)(CN)2]; more positive for 1,2-Nc than
for Pc is consistent with the expectation for the angular
π-extension of the porphyrinic framework.28 Since this redox
process is not perfectly reversible (nonsymmetrical redox pair
with relatively large separation), aggregation may occur near
the electrode surface. Therefore, when the applied potential
is higher than that of the first oxidation of the π-ligand,
electrolysis leads to the crystal growth of the π-radical
species. Coexistence of TPP yielded a partially oxidized salt,
TPP[Co(1,2-Nc-C4h)(CN)2]2. On the basis of its stoichiom-
etry, the formal charge of the [Co(1,2-Nc-C4h)(CN)2] unit
was determined to be -0.5; the Nc ligand is oxidized by
1/2e.
Figure 3. Molecular arrangement of the two Mg(1,2-Nc-C4h)H2O‚
(acetone)‚3(benzene) units in the crystal. Acetone molecules are drawn with
shaded spheres, and benzene molecules are drawn in light gray. Broken
lines are O-H‚‚‚O hydrogen bonds.
Crystal Structure of TPP[Co(1,2-Nc-C4h)(CN)2]2. Figure
5a shows the molecular arrangement of the partially oxidized
salt. In the analogous Pc conductor, TPP[Co(Pc)(CN)2]2, the
space group is P42/n.8 The space group for TPP[Co(1,2-Nc-
C4h)(CN)2]2 is changed to I41/a, and the Z value is doubled.
In both compounds, however, the CoIII ions and the centers
of TPP commonly occupy the 1h site and 4h site, respectively.
Therefore, one-half of Co(1,2-Nc-C4h)(CN)2 and one-quarter
of TPP are crystallographically independent. A structural
change in the molecular geometry of the 1,2-Nc-C4h ligand
upon oxidation could not be clearly seen due to the rather
large experimental ambiguity (Table 2).
The 1,2-Nc-C4h units form a one-dimensional chain along
the c axis, and the TPP cations are also one-dimensionally
aligned between the chains. The arrangement of the chains
and the TPP arrays are similar to that of TPP[Co(Pc)(CN)2]2.
The structure of the one-dimensional chain is shown in Figure
5b. The 1,2-Nc-C4h rings, which are translationally related
along the c axis, are stacked with overlaps at two of the four
peripheral naphthalene rings with interplanar distance of 3.44
Å. The distance is comparable to that in TPP[Co(Pc)(CN)2]2.8
A marked difference between the π-π overlap in the Pc
chain and that in the 1,2-Nc-C4h chain is the relative ring
orientation. The chain axis of the Pc chain nearly coincides
with one vertical mirror plane of each molecule with D4h
symmetry. The same overlap mode is impossible for the 1,2-
Nc-C4h chain due to the angular π-extension. The molecule
must now be rotated around the CN-Co-CN axis by about
12° to achieve the maximum π-π overlap (Figure 6a).
The π-π overlap in the 1,2-Nc-C4h chain is increased
compared with that of the Pc chain. However, the degree of
π-π interaction must be considered on the basis of the
molecular orbitals. Since the π-ligand is oxidized, the
HOMO-HOMO interaction is predominant. The HOMO
coefficients were calculated with the structural data using
an extended Hu¨ckel method, and the overlap integral between
the neighboring rings was estimated. The obtained value is
1.8 × 10-3, which is about one-fifth of that found in TPP-
Figure 4. UV-vis spectra of (a) Mg(1,2-Nc-C4h)H2O, (b) CoII(1,2-Nc-
C4h), and (c) K[CoIII(1,2-Nc-C4h)(CN)2] in pyridine.
Table 3. Major Absorption Bands of Pc and Nc Complexes in Pyridine
compound
Soret band/nm
Q-band/nm
Mg(1,2-Nc-C4h)H2O
Mg(Pc)H2Oa
383
347
354
333
403
346
688
674
666
659
685
675
CoII(1,2-Nc-C4h)
CoII(Pc)
K[CoIII(1,2-Nc-C4h)(CN)2]
K[CoIII(Pc)(CN)2]
a Reference 29.
Optical Properties. The UV-vis spectra of the Mg, CoII,
and CoIII complexes in pyridine are shown in Figure 4. The
sharp Q-band for each compound is consistent with the C4h
symmetry of the ligand, as observed in the spectra of the
isolated four isomers of Mg(1,2-Nc).18 The band position is
slightly red-shifted compared with that of the corresponding
Pc compound (7-14 nm), as shown in Table 3. On the other
hand, the Soret bands are largely red-shifted (21-57 nm)
compared with those of the corresponding Pc compounds.
All these features qualitatively agree with the energy-level
shifts expected for the π-extended porphyrinic frameworks;
the LUMO is slightly more stabilized than the HOMO, and
next-HOMO is largely destabilized in a 1,2-naphthalene-
fused porphyrin compared with those in tetrabenzoporphy-
rin.28
(28) Kobayashi, N.; Konami, H. J. Porphyrins Phthalocyanines 2001, 5,
233.
4174 Inorganic Chemistry, Vol. 45, No. 10, 2006

C4h Isomer of Metal(1,2-naphthalocyanine)
Figure 5. (a) Projection along the c axis of the crystal structure of TPP[CoIII(1,2-Nc-C4h)(CN)2]2. (b) One-dimensional chain of the partially oxidized
CoIII(1,2-Nc-C4h)(CN)2 units.
Figure 6. (a) Schematic representation of the molecular orientation in the Pc and 1,2-Nc stacking arrays. (b) Schematic representation of the HOMO
coefficients in the Pc and 1,2-Nc ligands.
[Co(Pc)(CN)2]2.8 Slight rotation of the Pc framework leads
to a significant influence on the π-π interaction. This is
thought to be because the HOMO coefficients at peripheral
rings are relatively small. In addition, rotation makes the
contact between the pyrrole carbon atoms, which have the
largest coefficient, in the neighboring 1,2-Nc-C4h rings less
efficient (Figure 6b).
Physical Properties of TPP[Co(1,2-Nc-C4h)(CN)2]2. The
temperature dependence of the single-crystal resistivity
(//c) of TPP[Co(1,2-Nc-C4h)(CN)2]2 is shown in Figure 7.
The room-temperature value (9 Ω cm) is about 3 orders of
magnitude higher than that of TPP[Co(Pc)(CN)2]2.8 The
temperature dependence is semiconducting with a small
activation energy of about 0.05 eV. Since the Nc units form
a uniform one-dimensional chain in which the repeat unit
coincides with the unit c length, the HOMO band is expected
to be three/fourths-filled metal-like. The inconsistency
Figure 7. Temperature dependence of the single-crystal electrical resistivity
(along the c axis) in (a) TPP[Co(1,2-Nc-C4h)(CN)2]2 and (b) TPP[Co(Pc)-
(CN)2]2.
between the band picture and the transport behavior may be
due to the extremely small overlap integral value, which is
approximately proportional to the transfer integral value (t
) one-quarter of the band width). The bandwidth in TPP-
[Co(1,2-Nc-C4h)(CN)2]2 is estimated as 0.12 eV on the basis
of the ratio of overlap integral values in TPP[Co(Pc)(CN)2]2
and TPP[Co(1,2-Nc-C4h)(CN)2]2. This value is significantly
smaller than the on-site Coulomb repulsion energy (typically
1 eV). Therefore, a simple band picture may not be applied
Inorganic Chemistry, Vol. 45, No. 10, 2006 4175

Gacho et al.
of the electron charge, and F is the ratio of holes to sites. In
the present case, F is 1/2, leading to S(Tf∞) ) 59.7 µV
deg-1. The value is in good agreement with the values we
have obtained, suggesting that in TPP[Co(1,2-Nc-C4h)(CN)2]2
the correlation between the charge carriers suppresses their
diffusive motion and hopping becomes predominant in
charge conduction. Interestingly, the thermoelectric power
of TPP[Co(Pc)(CN)2]2 is clearly metallic; S changes linearly
with temperature with a room-temperature value of about
40 µV deg-1. Therefore, the difference again suggests that
TPP[Co(Pc)(CN)2]2 is at the boundary between metallic and
CO states and TPP[Co(1,2-Nc-C4h)(CN)2]2 is in an insulating
CO regime.
Conclusion
Isolation of a preparative amount of the 1,2-Nc-C4h ligand
from the crude mixture, as well as preparation of its partially
oxidized one-dimensional conductor of axially CN ligated
species, has been reported. Despite the π-extended feature
compared with Pc, the π-π stacking interaction was
observed to be considerably reduced. Thus, the conductivity
showed apparent semiconducting behavior, and the thermo-
electric power indicated a Coulomb repulsion limited con-
stant value. The behavior may be explained by the CO
instability in a one/fourth-(hole)filled one-dimensional con-
ductor. Structural analysis did not indicate CO periodicity;
however, the extremely small t value in TPP[Co(1,2-Nc-C4h)-
(CN)2]2 may be preferable for such a charge localized ground
state compared with diffusive charge in a partially filled
metallic band.
Figure 8. Temperature dependence of the single-crystal thermoelectric
power (S; along the c axis) in (a) TPP[Co(1,2-Nc-C4h)(CN)2]2 and (b) TPP-
[Co(Pc)(CN)2]2.
for this system. The similar situation was also observed for
TPP[Co(Pc)(CN)2]2 in which the charge transport is weakly
thermally activated though the conduction band is three/
fourths-filled metal-like. For this crystal, the charge-ordered
(CO) instability due to both on-site and inter-site correlation
effects has been suggested.30,31 TPP[Co(Pc)(CN)2]2 is thought
to be situated at the boundary between metallic and CO
states. TPP[Co(1,2-Nc-C4h)(CN)2]2 may be situated com-
pletely in an insulating CO regime, since the bandwidth is
much narrower than that in the Pc analogue. Therefore, the
charge transport is assumed to occur by hopping of localized
charges.
The thermoelectric power behavior was also found to be
nonmetallic. The temperature dependence of the thermo-
electric power (//c) is shown in Figure 8. Above 100 K, the
thermoelectric power is constant with a value of about 60
µV deg-1. This behavior can be reproduced by the prediction
reported by Chaikin and Beni for the high-temperature limit
of the thermoelectric power in a system with a large Coulomb
repulsion.32 According to their paper, the high-temperature
limit of the thermoelectric power, S(Tf∞), in a system for
hole conduction with a large Coulomb repulsion is as follows
Acknowledgment. This work was supported in part by
a Grant-in-Aid for Scientific Research from the Ministry of
Education, Culture, Sports, Science and Technology of the
Japanese Government and a Grant-in-Aid for Scientific
Research from the Japan Society for the Promotion of
Science.
Supporting Information Available: 1H NMR spectra of K[Co-
(1,2-Nc-C4h)(CN)2] in DMSO-d6 and X-ray crystallographic files
in CIF format for Mg(1,2-Nc-C4h)H2O‚(acetone)‚3(benzene) and
TPP[CoIII(1,2-Nc-C4h)(CN)2]2. This material is available free of
charge via the Internet at http://pubs.acs.org.
S(Tf∞) ) (kB/e) ln[2(1 - F)/F],
where kB is the Boltzmann constant, e is the absolute value
(29) Whalley, M., J. Chem. Soc. 1961, 866.
IC0520622
(30) Seo, H.; Hotta, C.; Fukuyama, H. Chem. ReV. 2004, 104, 5005.
(31) Hotta, C.; Ogata, M.; Fukuyama, H. Phys. ReV. Lett. 2005, 95, 216402.
(32) Chaikin, P. M.; Beni, G. Phys. ReV. B 1976, 13, 647.
4176 Inorganic Chemistry, Vol. 45, No. 10, 2006