1P008
Synthesis and Properties of Axially-Ligated Co and Fe Phthalocyanines Partially-Oxidized Salts○Derrick Ethelbhert C. Yu,1 Toshio Naito,1,2 Tamotsu Inabe,1 Akira Kikuchi,1 Tetsuya Taketsugu,1Masaki Matsuda,3 and Hiroyuki Tajima3
1 Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo
2 Creative Research Initiative, Hokkaido University, Sapporo

3 Institute for Solid-State Physics, University of Tokyo, Kashiwa, Chiba

Partially-oxidized cobalt phthalocyanine salts with axial CN ligands, CoIII(Pc)(CN)2, are known
conductors primarily because their π-ligands are oxidized.1 This type of M(Pc)L2 compound can be avital component of molecular conductors due to the possibility of introducing different ligands andcentral metal atoms. These factors can lead to a variation in the π–π stacking structure of the molecularassemblies of the resulting compounds.2
Compared with L = CN compounds, L = X(halides) compounds have not been studied
in detail because the labile nature ofhalides makes it difficult to prepare thestarting complexes.3
Figure 1. 1-D stacking arrangements of metal phthalocyanines.
A direct reaction to oxidize MII(Pc) to [MIII(Pc)X2]- for M = Co and Fe, and X = Cl and Br is notknown; hence, a multi-step synthesis involving a series of general methods is utilized to prepare thepartially oxidized salts.4,5 However, this study has shown that the direct electrolysis of MII(Pc) withTPP+X- (TPP = tetraphenylphosphonium; X = Cl or Br) can result to produce the partially oxidized saltsof TPP[MIII(Pc)X2]2 (Scheme 1). Furthermore, electrolysis with TPP+I- in certain solvents has beenfound to give TPP[MIII(Pc)(CN)2]2 in one-step.
++N
N

N

M

NN+P

N

N

X-One-step
electrooxidation

NX
X=,BClr

P

N

NN

N

M

NN

N

X

2III

TPP[M (Pc)X2]2 Partially-Oxidized Salt+=I
PMII(Pc)

-1/2

X
N

-1/2

CN
N

TPP+ X-N

N
N

N

M
N

N

N

CN

2

TPP[MIII(Pc)(CN)2]2 Partially-Oxidized Salt

Scheme 1. General pathway for the one-step synthesis of TPP[MIII(Pc)L2]2.

The series of crystals obtained are isomorphous (Figure 2a). The MIII(Pc)L2 units form aone-dimensional π–π stacking network. TPP stacks one-dimensionally and is surrounded by theMIII(Pc)L2 formation. The MIII(Pc)L2 unit is formally oxidized by 0.5e, which translates into two MIII(Pc)L2units per TPP counter cation. π–π overlaps are between two benzene rings from each adjacentMIII(Pc)L2 moiety (Figures 2b and 2c).
The varying thickness of the axial ligands (twice of the van der Waals radii: CN = 3.4Å, Cl = 3.5Å,and Br = 3.7Å) results in different distances between the MIII(Pc)L2 moieties, thereby affecting theeffectiveness of the π–π overlap. This hypothesis was confirmed by the concurring results of the overlap
integral calculations using the extended Hückel method, thermoelectric power, magnetic susceptibility,and electrical conductivity measurements, which translate to the relative band widths (CN>Cl>Br) of theMIII(Pc)L2 moieties.

(b)
(a)
bc(c)

aFigure 2. (a) Crystal structure of TPP[CoIII(Pc)Cl2]2. Space group = P42/n; Tetragonal; Z=2; And computationalgraphical representation of the π-π overlap between the CoIII(Pc)Cl2 moieties: (b) top, and (c) side perspectives.

From the difference in axial ligand thickness, the effectiveness of the π-interaction between theM(Pc) units is expected tobe in the order CN>Cl>Br.
Br(a)
(b)
ClCl
However, the conductivity
CNCNBrfollowed this trend only in
the TPP[Co(Pc)L2]2 series.
Figure 3a indicates that theBr-ligated species, which
has the least effective π–πoverlap, has the highestT/K
T/K
electricalresistivity.
However, the Br species in Figure 3. Electrical resistivity along the conduction path (c-axis) of (a)the TPP[Fe(Pc)L2]2 series TPP[CoIII(Pc)L2]2, and (b) TPP[FeIII(Pc)L2]2.
(Figure 3b) showed lower
resistivity than its CN and Cl counterparts. One possible reason for this is since Fe3+ has magnetic spin,
the ligand field energy (CN>>Cl>Br) variably splits the Fe3+ d-orbitals (d5). Due to this, the degree ofscattering of the conduction π-electrons by the magnetic moment may be altered by the d-orbital energy.
1041041031021032ρ / Ω cm

ρ / Ω cm

10110010110010-1-11010-2-21010-3-31010150200250300

The magnetic susceptibility profile of the TPP[Fe(Pc)L2]2series shown in Figure 4. It has been reported for L = CN thatlarge anisotropy of susceptibility results from the very anisotropic
g-tensor of the Fe(Pc)(CN)2 unit. Such anisotropy is alsoobserved for L = Cl and Br, but the degree seems to be smaller.
The striking difference lies in the anomalies due to theantiferromagnetic interactions at low temperature (5-25K). Theanomaly is supposed to be related to the magnitude of the π-dinteraction, its lower degree and its occurrence at a lower
temperature in TPP[Fe(Pc)X2]2 than in TPP[Fe(Pc)(CN)2]2
signifies that the former has a smaller π-d interaction than thelatter.

50

100

150

200

250

300

250

300

0.20

BrBrClClCN
CN

0.15

-1100

χp / emu mol

50

0.10

⊥c//c
⊥c//c
⊥c//c

0.05

0.00
050

100

150

T/K

200

Figure 4. Magnetic susceptibility at 1Tof TPP[FeIII(Pc)L2]2.

Overall, this phenomenon can be attributed to the interaction between conduction π-electrons andlocalized d-spins in the [FeIII(Pc)L2]2 units. Moreover, to further study these π-d systems, corroborating
data from g-tensor anisotropy, magnetoresistance and magnetic torque measurements, as well as
quantum chemical calculations for FeIII(Pc)L2 in order to evaluate the effect or influence of the axial
ligands on the d-centered energy levels, are now in progress.
References 1) T. Inabe, J. Porph. Phthal. 2001, 5, 3; 2) T. Inabe, and H. Tajima, Chem. Rev. 2004, 104, 5503; 3) D.E.C. Yu, H. Imai, M. Ushio, S. Takeda, T.
Naito, and T. Inabe, Chem. Lett. 2006, 35, 602; 4) J.F. Myers, G.W. Canham, and A.B.P. Lever, Inorg. Chem. 1975, 14, 461; 5) C. Hedtmann-Rein, M.
Hanack, K. Peters, E. Peters, and H. G. von Schnering, Inorg. Chem. 1987, 26, 2647.