Structure and magnetic properties of a low-spin manganese(III) phthalocyanine dicyanide complex

Article abstract of DOI:10.1246/cl.2005.1524

A manganese(III) complex salt, TPP[Mn^III(Pc)(CN) ₂]· DCM was crystallized in dichloromethane solution (Pc = phthalocyaninato, TPP⁺ = tetraphenylphosphonium, and DCM = dichloromethane). In the crystal, Pc molecules form a pair of one-dimensional regular chains along the c axis. The magnetic susceptibility measurement revealed Mn ions in the low-spin state (S = 1) and a spin-orbit coupling effect due to the incomplete quenching of the angular orbital moment under the symmetrical ligand field. Copyright

Full text of DOI:10.1246/cl.2005.1524

1524
Chemistry Letters Vol.34, No.11 (2005)
Structure and Magnetic Properties
of a Low-spin Manganese(III) Phthalocyanine Dicyanide Complex
Masaki Matsuda,ꢀ Jun-Ichi Yamaura, Hiroyuki Tajima, and Tamotsu Inabey
Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581
yDivision of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810
(Received August 26, 2005; CL-051099)
III
.
A manganese(III) complex salt, TPP[Mn (Pc)(CN)2]
DCM was crystallized in dichloromethane solution (Pc =
phthalocyaninato,
TPPþ = tetraphenylphosphonium,
and
DCM = dichloromethane). In the crystal, Pc molecules form a
pair of one-dimensional regular chains along the c axis. The
magnetic susceptibility measurement revealed Mn ions in the
low-spin state (S ¼ 1) and a spin–orbit coupling effect due to
the incomplete quenching of the angular orbital moment under
the symmetrical ligand field.
Manganese phthalocyanine and porphyrin are quite useful
modeling compounds for biomaterials and intermediates in bio-
logical reactions. Low-spin manganese(III) complexes with S ¼
1 state are particularly important, because they are isoelectronic
with the elusive iron(IV) species. Although there have been sev-
eral reports on manganese(III) porphyrins, in most of these stud-
ies the porphyrins have been in a high-spin S ¼ 2 state.1 This
implies that a very strong ligand field is required to impose a
low-spin S ¼ 1 state on the manganese(III) ion. To the best of
our knowledge, the diimidazolate and dicyanide complexes are
the only cases of manganese(III) porphyrins in a low-spin
state.2–4 For phthalocyanine, only the spectroscopic properties
have been reported for the dicyano complex, and there are few
data on the molecular structure and few magnetic studies.5,6 In
this letter, we describe the preparation, structure, and magnetic
properties of a newly synthesized manganese(III) phthalocya-
Figure 1. Molecular structures of TPP and [MnIII(Pc)(CN)2].
Mn2 are 178.6(6) and 178.0(7)ꢁ, respectively. The length
between the Mn ion and cyanide ligand (d(Mn1–CCN) =
ꢀ
ꢀ
2.025(7) A and d(Mn2–CCN) = 2.015(7) A) is longer than those
in the [CoIII(Pc)(CN)2] and [FeIII(Pc)(CN)2] units,10 reflecting
the larger ionic radius of MnIII compared with CoIII and FeIII.
Since the ligand fields of CN and Pc are strong, it is considered
that the Mn ion adopts the low-spin state with a d-electron
configuration (dxy)2 (dyz)1 (dzx)1.
Figure 2 shows the crystal structure of TPP[MnIII(Pc)-
(CN)2] DCM. The two unique [Mn (Pc)(CN)2] units form a
one-dimensional regular chain (chain1 includes Mn1 and chain2
includes Mn2) along the c axis, and the chain1 is almost perpen-
dicular to the chain2. The interplanar distances between the
III
.
III
.
nine complex, TPP[Mn (Pc)(CN)2] DCM (TPP = tetraphenyl-
phosphonium, DCM = dichloromethane). This is the first report
of the structural characterization and magnetic study of the low-
spin manganese(III) phthalocyanine complex.
ꢀ
peripheral benzene rings are 3.32 and 3.40 A for chain1, and
ꢀ
3.36 and 3.49 A for chain2, respectively. Although these values
are almost the same as the summation of the van der Waals
ꢀ
Mn(Pc) was prepared by the method of Rutter and
McQueen.7 The obtained crystals (0.5 g) were dissolved in etha-
nol (100 mL), and KCN (0.25 g) was added. After stirring for
72 h, a manganese(III) complex salt, K[Mn(Pc)(CN)2], was
obtained (0.4 g). The same salt could be obtained by the similar
reaction of Mn(Pc)Cl (Aldrich Products) with KCN in EtOH.
The cation exchange was carried out by metathesis of K[Mn(Pc)-
(CN)2] (0.33 g) with TPPBr (0.43 g) in acetonitrile (150 mL).
The TPP salt was dissolved in dichloromethane and slow evap-
oration was done at room temperature. Black crystals of
radius of 3.4 A, the ꢀ–ꢀ interaction between Pc molecules could
not be expected, since the overlaps are insufficient. By the ex-
tended Huckel calculation,11 the overlap integral between the
¨
Pc molecules along the c axis is estimated to be 2:69 ꢂ 10ꢃ3
for chain1 and 1:86 ꢂ 10ꢃ3 for chain2, and these values are less
than 30% of those for TPP [MIII(Pc)(CN)2]2 (M ¼ Fe and Co).10
This confirms the insignificance of the ꢀ–ꢀ interaction between
III
.
TPP[Mn (Pc)(CN)2] DCM, which were suitable for X-ray
crystal structure determination, were obtained.8
The molecular structures of TPP and [MnIII(Pc)(CN)2] are
shown in Figure 1. There are two crystallographically independ-
ent [MnIII(Pc)(CN)2] molecular units. The central Mn ions of
each unit lie at the inversion center. The bond lengths and angles
of the phthalocyaninato core are not very different from those of
the Mn(Pc) molecule.9 The cyanide ligands are coordinated in a
trans configuration, and the angles of Mn–C–N for Mn1 and
III
.
Figure 2. Crystal structure of TPP[Mn (Pc)(CN)2] DCM;
view along the c axis (a) and the a axis (b).
Copyright ꢀ 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.11 (2005)
1525
low-spin state, Kotani calculated the temperature dependence
of the magnetic moment by taking account of the spin–orbit cou-
pling effect,14 and Buschmann et al. experimentally estimated
the spin–orbit coupling with the Kotani model.15 Although the
molecular symmetry of the [MnIII(Pc)(CN)2] unit is lower than
that of [MnIII(CN)6] and we can not apply the Kotani model to
the [MnIII(Pc)(CN)2] system, the relatively highly symmetrical
ligand field of D4h yields degenerated dxz and dyz orbitals, which
possess two unpaired electrons. This situation would also lead to
the incomplete quenching of the angular orbital moment and the
Figure 3. Absorption spectrum of TPP [MnIII(Pc)(CN)2].
the Pc molecules.
spin–orbit coupling in the [MnIII(Pc)(CN)2] system. Actually,
III
.
Figure 3 represents the UV–vis absorption spectrum for
TPP[MnIII(Pc)(CN)2] in DCM solution. The spectrum is almost
consistent with those previously reported for the analogues.5,6
The Q band, which corresponds to the transition between
HOMO (a1u) and LUMO (eg), is observed at 671 nm. The B
(Soret) band is observed at 325 nm and corresponds to the exci-
tation between NHOMO (a2u) and LUMO (eg). The peak at
614 nm may be assigned to the splitting of the Q band caused
by the vibronic coupling which is characteristic for most metal
phthalocyanine complexes.6,12 The peak around 638 nm could
be attributed to the LMCT (from Pc to dyz or dzx), since the peak
is not observed for closed-shell (dxy)2(dyz)2(dzx)2 complexes
composed of the [FeII(Pc)(CN)2] or [CoIII(Pc)(CN)2] unit.6,10
The peaks around 558, 498, 436, and 388 nm could be also attrib-
uted to the LMCT and/or MLCT bands.6,13
the temperature dependence of ꢁꢃ1 for TPP[Mn (Pc)(CN)2]
DCM resembles that for [(Ph3P)2N]3[MnIII(CN)6] reported by
Buschmann et al. We, therefore, consider that the extraordinary
ꢂeff value and its temperature dependence observed for
TPP[Mn (Pc)(CN)2] DCM should be caused by the spin–orbit
coupling, as seen in the [MnIII(CN)6] system.
III
.
In summary, we have succeeded in solving the crystal struc-
ture of the manganese phthalocyanine complex, TPP[MnIII(Pc)-
.
(CN)2] DCM in the low-spin state (S ¼ 1), for the first time. The
temperature dependence of the magnetic susceptibility suggests
the spin–orbit coupling effect due to the symmetrical ligand field
in this system.
This work was supported in part by Grant-in-Aid for
Scientific Research from the Ministry of Education, Culture,
Sports, Science and Technology of the Japanese Government
and Grant-in-Aid for Scientific Research of Japan Society for
the Promotion of Science.
Figure 4a shows the temperature dependence of the magnet-
ic susceptibility (ꢁ) under an applied field of 1 T for polycrystal-
III
.
lines of TPP[Mn (Pc)(CN)2] DCM. The effective moment
(ꢂeff) and the reciprocal susceptibility (ꢁꢃ1) are also plotted
in Figure 4b. The ꢁꢃ1 data are almost linear above 75 K and
can be fitted by the Curie–Weiss expression. The Curie and
Weiss constants obtained are 1.67 emu K molꢃ1 and 0.84 K,
respectively. The ꢂeff at the room temperature is 3.28 mB, which
is considerably higher than the calculated spin-only value of
2.83 mB for S ¼ 1. Similarly, large values are reported for the
low-spin manganese(III) porphyrin dicyanide complexes, in
which the ꢂeff value is elevated by the spin–orbit coupling effect
and/or magnetic anisotropy.2,3
References and Notes
1
2
L. J. Boucher, Coord. Chem. Rev., 7, 289 (1972).
L. Galich, H. Huckstadt, and H. Homborg, J. Porph. Phthal., 2, 79
(1998).
¨
¨
3
4
A. P. Hansen and H. M. Goff, Inorg. Chem., 23, 4519 (1984).
J. T. Landrum, K. Hatano, W. R. Scheidt, and C. A. Reed, J. Am. Chem.
Soc., 102, 6729 (1980).
5
6
G. Engelsma, A. Yamamoto, E. Markham, and M. Calvin, J. Phys.
Chem., 66, 2517 (1962).
S. Sievertsen, H. Grunewald, and H. Homborg, Z. Anorg. Allg. Chem.,
619, 1729 (1993).
H. A. Rutter and J. D. McQueen, J. Inorg. Nucl Chem., 12, 362 (1960).
The ꢂeff value decreases remarkably below 60 K, a behavior
that is remindful of an intermolecular antiferromagnetic interac-
tion. However, the distance between the Mn ions is extremely
7
8
Crystal data for TPP[MnIII(Pc)(CN)2] DCM: C59H38Cl2N10MnP, tri-
.
ꢁ
ꢀ
ꢀ
ꢁ
clinic, space group P1, a ¼ 13:0468ð9Þ A, b ¼ 22:393ð2Þ A, c ¼
ꢁ
ꢁ
ꢀ
8:9859ð6Þ A, ꢃ ¼ 101:034ð2Þ , ꢄ ¼ 95:391ð2Þ , ꢅ ¼ 74:430 , V ¼
ꢀ
long (8.986 A), and there is no carrier that can mediate the
ꢀ 3
2479:7ð3Þ A , Z ¼ 2, Dcalcd ¼ 1:398 g cmꢃ3, Bruker SMART APEX
system at 293 K, Mo Kꢃ, ꢂ(Mo Kꢃ,) = 4.45 cmꢃ1, 24115 reflections
measured, 12336 independent reflections, 4076 reflections with
I > 2ꢆðIÞ, R ¼ 0:052, RW ¼ 0:086 (12331 reflections refined with
I > 0ꢆðIÞ, 662 variables). CCDC-284241
spin–spin interaction. Thus the antiferromagnetic interaction
should be excluded. For the [Mn(CN)6]3ꢃ compound, which is
one of the rare examples of a manganese(III) complex with a
9
a) J. F. Kirner, W. Dow, and W. R. Scheidt, Inorg. Chem., 15, 1685
(1976). b) R. Mason, G. A. Williams, and P. E. Fielding, J. Chem.
Soc., Dalton Trans., 1979, 676.
10 M. Matsuda, T. Naito, T. Inabe, N. Hanasaki, H. Tajima, T. Otsuka,
K. Awaga, B. Narymbetov, and H. Kobayashi, J. Mater. Chem., 10,
631 (2000).
11 T. Mori, A. Kobayashi, Y. Sasaki, H. Kobayashi, G. Saito, and H.
Inokuchi, Bull. Chem. Soc. Jpn., 57, 627 (1984).
12 T. C. VanCott, J. L. Rose, G. C. Misener, B. E. Williamson, A. E.
Schrimpf, M. E. Boyle, and B. E. Williamson, J. Phys. Chem., 93,
2999 (1989).
13 B. E. Williamson, T. C. VanCott, M. E. Boyle, G. C. Misener, M. J.
Stillman, and P. N. Schatz, J. Am. Chem. Soc., 114, 2412 (1992).
14 M. Kotani, J. Phys. Soc. Jpn., 4, 293 (1949).
15 W. E. Buschmann, L. L.-Sands, A. L. Rheingold, and J. S. Miller,
Inorg. Chim. Acta., 284, 175 (1999).
Figure 4. Temperature dependence of the magnetic susceptibil-
III
.
ity (a) and the magnetic moment (b) for TPP[Mn (Pc)(CN)2]
DCM. The inset shows the reciprocal susceptibility.
Published on the web (Advance View) October 8, 2005; DOI 10.1246/cl.2005.1524