Crystal structures and magnetic properties of manganese(III) complexes with tridentate Schiff base ligands

Article abstract of DOI:10.1007/s10847-015-0492-0

Manganese(III) complexes [MnL ₂ ¹ ]BPh₄ (1) and [MnL ₂ ² (MeOH)₂]BPh₄ (2) were synthesized (HL¹ = 2-{N-[2-(2-pyridyl)ethyl]iminomethyl}-6-methoxyphenol and HL² = 2-{N-[2-(2-pyridyl)ethyl]iminomethyl}-4-methylphenol) and characterized. The crystal structures were determined by single crystal X-ray crystallography for 1 and 2 and magnetic properties were characterized by magnetic susceptibility. Compounds 1 and 2 crystallized in the triclinic system with space groups P-1. The crystal structure of 1 showed that the central manganese(III) ions were coordinated by four nitrogen and two oxygen atoms of two ligands in trans positions, exhibiting a pseudo-octahedral geometry. On the other hand, the crystal structure of 2 showed that the manganese(III) ions were coordinated by the two nitrogen and two oxygen atoms of two ligands and two methanol solvent molecules. The variable temperature-dependence magnetic susceptibilities have shown that the compounds 1 and 2 manganese(III) oxidation state; there is no magnetic interaction between complexes.

Full text of DOI:10.1007/s10847-015-0492-0

J Incl Phenom Macrocycl Chem
DOI 10.1007/s10847-015-0492-0
ORIGINAL ARTICLE
Crystal structures and magnetic properties of manganese(III)
complexes with tridentate Schiff base ligands
•
Hitomi Ohmagari Aya Fukahori Manabu Nakaya
•
•
•
Ryo Ohtani Shinya Hayami Masaaki Nakamura
•
Received: 29 January 2015 / Accepted: 2 March 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract Manganese(III) complexes [MnL12]BPh4 (1)
and [MnL22(MeOH)2]BPh4 (2) were synthesized (HL1 = 2-
{N-[2-(2-pyridyl)ethyl]iminomethyl}-6-methoxyphenol and
HL2 = 2-{N-[2-(2-pyridyl)ethyl]iminomethyl}-4-methylphe-
nol) and characterized. The crystal structures were determined
by single crystal X-ray crystallography for 1 and 2 and
magnetic properties were characterized by magnetic suscep-
tibility. Compounds 1 and 2 crystallized in the triclinic system
with space groups P-1. The crystal structure of 1 showed that
the central manganese(III) ions were coordinated by four ni-
trogen and two oxygen atoms of two ligands in trans positions,
exhibiting a pseudo-octahedral geometry. On the other hand,
the crystal structure of 2 showed that the manganese(III) ions
were coordinated by the two nitrogen and two oxygen atoms
of two ligands and two methanol solvent molecules. The
variable temperature-dependence magnetic susceptibilities
have shown that the compounds 1 and 2 manganese(III)
oxidation state; there is no magnetic interaction between
complexes.
Introduction
Manganese ions and their complexes are significant not only
for redox properties in biochemical processes, but also for
magnetic properties [1–13]. There has been considerable
interest in designing manganese complexes that
are mononuclear, binuclear, trinuclear or polynuclear in
order to induce catalytic, photo, magnetic or biometric
properties. Manganese complexes with Schiff base ligands
have been investigated because these type of ligands
often present biometric properties that mimic structural
features of a biological active site [14–16]. Almost of these
manganese complexes are polynuclear using N2O2 salen
type ligands. On the other hand, mononuclear mangane-
se(III) complexes with the N2O tridentate ligand, 2-{N-[2-
(2-pyridyl)ethyl]iminomethyl}phenol, was reported in 1996
[17]. The manganese ion occupies a crystallographic in-
version center, adopting an elongated octahedral geometry,
being bound to two phenolic oxygen atoms, two imine ni-
trogen atoms, and two pyridyl nitrogen atoms from two
Schiff base ligands, L; each of these act as a facial tridentate
chelate ring. The N2O2 atoms coordineted the manganese
ion in the same plane. The bond distances in the plane [Mn–
Keywords Manganese(III) complex Á Schiff base ligand Á
Magnetic property
˚
O = 1.87 A, Mn–N = 2.01 A], is close to those of other
˚
manganese(III) complexes with Schiff base ligands. The
˚
axial bonds involving pyridyl nitrogens [Mn–N = 2.29 A]
are considerably longer than the in-plane bond distances.
This octahedral elongation may be a consequence of the
Jahn–Teller effect expected for a high-spin d4 ion.
H. Ohmagari Á A. Fukahori Á M. Nakaya Á R. Ohtani Á
S. Hayami Á M. Nakamura (&)
Department of Chemistry, Graduate School of Science and
Technology, Kumamoto University, 2-39-1 Kurokami,
Kumamoto 860-8555, Japan
Here we have focused on tridentate N2O-donor ligands of
the above type but with methyl (HL1) or methoxyl (HL2)
subsituents (HL1 = 2-{N-[2-(2-pyridyl)ethyl]iminomethyl}-
6-methoxyphenol, and HL2 = 2-{N-[2-(2-pyridyl)ethyl]imi-
nomethyl}-4-methylphenol) (Scheme 1) in order to elucidate
the structural details of their manganese(III) complexes. Two
e-mail: nakamura@sci.kumamoto-u.ac.jp
S. Hayami
Institute of Pulsed Power Science (IPPS), Kumamoto University,
2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan
123

J Incl Phenom Macrocycl Chem
manganese(III) complex, [Mn(L1)2]BPh4 (1) and [Mn(L2)2(-
MeOH)2]BPh4 (2), were prepared and investigated.
slowly, and after 3 days, the compound 1 was obtained
scaly brown crystals. The compound 2 was also obtained
by the same method. [Mn(L1)2]BPh4 (1), Anal. Calcd. For
C54H50O2N4Mn1B1: C, 69.57; H, 5.56; N, 7.73. Found: C,
73.36; H, 6.38; N, 6.11. IR (cm-1): 1618, 1601.
[Mn(L2)2(MeOH)2]BPh4 (2), Anal. Calcd. For C56H56O6-
N4Mn1B1: C, 70.89; H, 6.16; N, 5.90. Found: C, 70.89; H,
6.16; N, 5.90.
Experimental section
Synthesis
The preparation of the ligands L1 and L2 and the com-
pounds 1 and 2 were essentially carried out according to
the literature with minor modifications [17].
Crystallographic data collection and structural
determination
2-{N-[2-(2-pyridyl)ethyl]iminomethyl}-4-methylphenol
(L1) was synthesized by following method. 2-(2-ami-
noethyl)pyridine (0.122 g, 1.00 mmol) was added to a so-
lution of 5-methylsalicylaldehyde (0.134 g, 1.00 mmol) in
MeOH (20 ml) and stirred for 30 min at 60 °C. After then,
L1 was obtained as yellow oil product. 1H NMR
(500 M Hz, CDCl3) d = 8.62 (1H, py-H), 8.11 (1H, N=C),
7.67–7.23 (3H, py-H), 7.25 (1H, Ar–H), 6.92-6.64 (2H,
Ar–H), 5.0 (1H, O–H), 3.88 (2H, N–CH2), 3.24 (2H, py-
CH2), 2.35 (3H, Ar–CH3). 2-{N-[2-(2-pyridyl)ethyl]imi-
nomethyl}-6-methoxyphenol was also synthesized as fol-
lowing. 2-(2-aminoethyl)pyridine (0.122 g, 1.00 mmol)
was added to a solution of o-vanillin (0.152 g, 1.00 mmol)
in MeOH (20 ml) and stirred for 30 min at 60 °C. After
then, L2 was obtained as yellow oil product. 1H NMR
(500 M Hz, CDCl3) d = 8.62 (1H, py-H), 8.11 (1H, N=C),
7.67–7.23 (3H, py-H), 7.01–6.63 (3H, Ar–H), 5.0 (1H, O–
H), 3.73 (3H, O–CH3), 3.88 (2H, N–CH2), 3.24 (2H, py-
CH2). IR (cm-1): 1609, 1601.
X-ray crystallographic data for 1 at 100 K (C54H50O2N4-
crystal
Mn1B1):
F.W. = 852.76,
brown
block
(0.756 9 0.551 9 0.161), triclinic, space group P-1(#2),
˚
˚
˚
a = 9.1899(5) A, b = 10.8090(6) A, c = 22.923(2) A, a =
86.513(2)°, b = 79.916(2)°, c = 84.350(2)°, V =
3
2228.8(3) A , Z = 2, Dcalcd = 1.271 g cm-3. The structure
was solved by direct methods and expanded using Fourier
techniques. The refinements by full matrix least-squares
gave an R factor of 0.0402 and a weighted R factor (RW) of
0.1148 from 33,835 reflections with intensity I [ 2r(I) for
562 variables; linear absorption coefficient l(M0
Ka) = 3.429 cm-1. The non-hydrogen atoms were refined
anisotropically.
˚
X-ray crystallographic data for 2 at 100 K (C56H58O6-
N4Mn1B1): F.W. = 948.85, brown block crystal
(0.100 9 0.100 9 0.100), triclinic, space group P-1(#2),
˚
˚
˚
a = 11.4507(2) A, b = 14.6649(3) A, c = 16.3917(3) A,
The manganese(III) compounds 1 and 2 were prepared
by mixing manganese(II) ion and ligands L1 and L2 in
MeOH solvent as follows. The ligands L1 (1.00 mmol) in
MeOH (20 ml) was added into a solution of Mn(CH3-
COO)2 Á 4H2O (0.245 g, 1.00 mmol) in MeOH (40 ml) and
stirred vigorously for 24 h under atmosphere to oxide
Mn(II) to Mn(III). Then NaBPh4 (0.163 g, 1 mmol) in
MeOH (100 ml) was added to the [Mn(L1)2]? solution
a = 64.5729(7)°, b = 79.8789(7)°, c = 83.5299(7)°, V =
3
2445.0(8) A , Z = 2, Dcalcd = 1.289 g cm-3. The struc-
˚
ture was solved by direct methods and expanded using
Fourier techniques. The refinements by full matrix least-
squares gave an R factor of 0.0373 and a weighted R factor
(RW) of 0.0612 from 11,199 reflections with intensity
I [ 2r(I) for 632 variables; linear absorption coefficient
l(M0 Ka) = 3.254 cm-1. The non-hydrogen atoms were
refined anisotropically.
NMR spectrum measurements
N
N
1H-NMR were measured on a JEOL (300-ECX) instrument
operating at 300 MHz (using the deuterated solvents as the
lock and residual solvent tetramethylsilane as the internal
reference).
N
OH
N
OH
O
IR spectrum measurements
L1
L2
IR spectrum was measured on a FT-IR instrument (using
dried KBr as the standard substance).
Scheme 1 Schematic structures of the ligands L1 and L2
123

J Incl Phenom Macrocycl Chem
Fig. 1 a ORTEP drawing of 1
at 100 K showing 50 %
(a)
probability displacement
ellipsoids. b Projection of the
crystal structure of 1 along
(b) the bc place and c the ab
plane. BPh-4 ions and H atoms
are omitted for clarity. Black
dashed lines are p–p
Mn(1)
O(1)
N(3)
N(4)
N(1)
N(2)
Mn(2)
O(2)
interactions, and red dashed
lines are CH–p interactions.
(Color figure online)
(b)
o
c
b
(c)
o
b
a
3.51 Å
2.97 Å
3.45 Å
Susceptibility measurements
Results and discussion
The magnetic susceptibilities for 1 and 2 between 5 K
and 300 K were measured with superconducting
The crystal structures of manganese(III) compounds 1 and
2 were determined at 100 K, and ORTEP drawings and
crystal packing views for 1 and 2 are shown in Figs. 1 and
2. The compound 1 with L1 bearing a methyl group was
crystallized in the space group P-1. There are two different
a
quantum interference device (SQUID) magnetometer
(Quantum Design MPMS-5S) in an external field of
0.5 T.
123

J Incl Phenom Macrocycl Chem
Fig. 2 a ORTEP drawing of 2
at 100 K showing 50 %
probability displacement
(a)
ellipsoids, b the bc place
O(2)
N(1)
packing view and c CH–p
interaction and projection of the
crystal structure of 2 along and
BPh-4 ions and H atoms are
omitted for clarity, in (a), (b),
and (c). (Color figure online)
O(4)
Mn(1)
Mn(2)
N(2)
N(4)
O(1)
N(3)
O(5)
(b)
b
o
c
(c)
Mn(2)
2.76 Å
Mn(1)
Mn(1)
2.76 Å
a
Mn(2)
c
o
b
˚
Mn(1)–N(3), are 2.2932(15) and 2.3131(16) A, respec-
manganese(III) ion sites, Mn(1) and Mn(2), in a unit cell,
and their manganese ions are coordinated to four nitrogen
and two oxygen atoms from two ligands of L1 in a fac-
arrangement. Mn–N(pyridine) distances, Mn(1)–N(1) and
tively. The Mn–N(imine) distances (Mn–N(2) =
˚
2.0247(14) and Mn–N(4) = 2.0293(14) A) are longer than
the Mn–N(pyridine) distances. Mn–O distances (Mn(1)–
123

J Incl Phenom Macrocycl Chem
Fig. 3 vmT versus T plots for
compound a 1 and b 2. (Color
figure online)
˚
O(1) = 1.8809(11) and Mn(1)–O(2) = 1.8706(14) A) are
also a consequence of the Jahn–Teller effect expected for a
high-spin d4 ion. The bond distances for the Mn(2) site and
the coordination environment are similar to those of
the Mn(1) site. Compound 2 also forms intramolecular
hydrogen bonding between N(pyridine)ÁÁÁH(MeOH) atom
shorter than Mn–N(pyridine and imine) distances. The
˚
axial bonds [Mn–N(pyridine) = 2.30 A] are considerably
longer than the in-plane bond distances [Mn–N(imi-
˚
˚
ne) = 2.03 A and Mn–O = 1.88 A]. From the results of
bond length, the complex formed elongated octahedral
structure due to Jahn–Teller effect of a high-spin d4 ion.
For the Mn(2) site, the bond distances are similar to those
for the Mn(1) site. However, the coordination environment
of Mn(2) is completely different from the Mn(1) site. The
ligand L1 of Mn(2) complex distorted in the ethyl moiety
due to the steric hindrances of BPh-4 counter anion. Com-
pound 1 forms two columns in the crystal packing, and one
involves the Mn(1) site with CH-p interactions between
methyl group and phenol ring and p–p interactions be-
˚
˚
(1.80 A). Furthermore, a CH–p interaction (2.76 A) be-
tween phenol ring in the Mn(1) and methoxyl in the Mn(2)
sites (Fig. 2b) occurs. As a result, the compound 2 forms
a 2-D structure in the ab plane with BPh-4 ions present in
the layers (Fig. 2c).
To investigate the effect of structural difference on
magnetic properties, the temperature dependence of the
magnetic susceptibility of 1 and 2 were measured in the
form of a vmT versus T curve, where vm is the molar
magnetic susceptibility and T the temperature. The vm-
T value for 1 is 2.80 cm3 Kmol-1 at 300 K, which is in the
range expected for high-spin manganese(III) ion (S = 2).
The vmT value is constant in the temperature range of
300–30 K, and then the value gradually decreases on fur-
ther cooling because of zero field splitting (Fig. 3a). In the
compound 2, the vmT value is 3.05 cm3 Kmol-1 at 300 K,
and the value is also corresponds to high-spin mangane-
se(III) ion. The vmT value is constant in the temperature
range of 300–30 K, and then the value gradually decreases
on further cooling because of zero field splitting (Fig. 3b).
When the sample was heated, even at 400 K, the magnetic
behavior shows the same trace indicating no loss of MeOH
ligands from the manganese(III) ion centers.
˚
tween phenol rings in the ab plane (2.97 and 3.51 A, re-
spectively), and another involves the Mn(2) site without
intermolecular interaction (Fig. 1b and c). Furthermore, p–
˚
p interactions between pyridine rings (3.45 A) are ob-
served for the Mn(1) column. As a result, the crystal
packing forms a 2-D structure along ab the plane (Fig. 1c).
In compound 2, there are also two different manganese(III)
ion sites, Mn(1) and Mn(2), in the unit cell and the struc-
ture of 2 incorporating L2 with a methoxyl group is dif-
ferent from that of 1 (Fig. 2a). The imine nitrogen and
phenolic oxygen atoms in two L2 ligands are coordinated
to a manganese(III) ion, but the pyridyl nitrogen atoms do
not coordinate to this ion. Instead of the pyridyl nitrogens
two MeOH molecules are coordinated to the mangane-
se(III) ion. The two Mn–N(imine) distances, Mn(1)–N(1)
˚
and Mn(1)–N(2), are 2.0510(11) and 2.0513(12) A, re-
Conclusion
spectively. The Mn–O distances (Mn–O(1) = 1.8619(12)
˚
and Mn–O(2) = 1.8660(11) A) are longer than the Mn–
In summary, the ligands L1 and L2 were prepared by
modifing methyl or methoxyl groups to known ligand of
tridentate Shiff base L. These manganese(III) complexes
[Mn(L1)2]BPh4 (1) and [Mn(L2)2(MeOH)2]BPh4 (2) in-
corporating L1 and L2 were synthesized and their crystal
N(imine) distances. The axial bonds [Mn–O(MeOH) =
˚
2.2330(11) and 2.2383(11) A] are considerably longer than
the in-plane bond distances [Mn–N(imine) and Mn–O].
From the results of bond length, the complex structure is
123

J Incl Phenom Macrocycl Chem
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