A novel (μ-OAc)2 bridged unsymmetric coordinated binuclear Mn(II) macrocyclic complex with ligating pendant-arm

Article abstract of DOI:10.1016/j.inoche.2008.09.001

A novel binuclear manganese Mn(II) macrocyclic complex with two pyridylmethyl pendant arms, [Mn₂^II(H₂L)(μ-OAc)₂](ClO₄)₂ · H₂O, has been synthesized and characterized crystallographically and magnetically. The crystal structure of the complex shows that two manganese ions locate in the same head of the macrocycle, leaving an uncoordinating cavity to catch protons through oxide of phenolate and the nearby imine groups in another head. The electrochemical study demonstrates that the complex gives two couples of redox peaks with E_1/2 of 0.3775 V and 0.8409 V, respectively. The variable temperature magnetic susceptibility measurement on the sample displays weak antiferromagnetic interaction between two manganese (II) with the J = -3.733(7) cm^-1. This complex exhibits a moderate activity for catalyzing disproportionation of H₂O₂ to O₂.

Full text of DOI:10.1016/j.inoche.2008.09.001

Inorganic Chemistry Communications 11 (2008) 1363–1366
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
A novel (l-OAc)2 bridged unsymmetric coordinated binuclear Mn(II)
macrocyclic complex with ligating pendant-arm
*
Zhi-Quan Pan , Wen-Hao Ni, Hong Zhou, Xue-Lei Hu, Qi-Mao Huang, Juan Kong
Key Laboratory for Green Chemical Process of Ministry of Education, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan 430073, PR China
Station Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel binuclear manganese Mn(II) macrocyclic complex with two pyridylmethyl pendant arms,
[Mn2II(H2L)(
l
-OAc)2](ClO4)2 ꢀ H2O, has been synthesized and characterized crystallographically and mag-
Received 15 May 2008
Accepted 2 September 2008
Available online 8 September 2008
netically. The crystal structure of the complex shows that two manganese ions locate in the same head of
the macrocycle, leaving an uncoordinating cavity to catch protons through oxide of phenolate and the
nearby imine groups in another head. The electrochemical study demonstrates that the complex gives
two couples of redox peaks with E1/2 of 0.3775 V and 0.8409 V, respectively. The variable temperature
magnetic susceptibility measurement on the sample displays weak antiferromagnetic interaction
between two manganese (II) with the J = ꢁ3.733(7) cmꢁ1. This complex exhibits a moderate activity
for catalyzing disproportionation of H2O2 to O2.
Keywords:
Binuclear Mn(II)complex
Crystal structure
Magnetic property
Electrochemistry
Catalytic oxidation
Ó 2008 Elsevier B.V. All rights reserved.
In recent decades, the design and synthesis of mononuclear
macrocyclic complexes with dinucleating ligands capable of bind-
ing two metal ions in close proximity, are of great interest, owing
to their promising applications in recognizing receptors of charged
ions and/or neutral small molecules [1,2], selecting cations to serve
as chemical sensors [3] and molecular devices [4]. The mononu-
clear macrocyclic complexes have been also used in synthesizing
hetero-dinuclear complexes [5,6] and mimicking catalytic activity
of enzymes as host–guest complexes [7]. Although some mononu-
clear macrocyclic complexes and cryptates, which could recognize
proton through uncoordinated site [5], were synthesized, the dinu-
clear macrocyclic complexes with an uncoordinating bigger cavity,
which is able to catch proton in the macrocycle, are rarely pro-
duced. Here we reported this kind of novel dinuclear manganese
(II) complex with pendant-arm macrocyclic Schiff base ligand in
which the metals are coordinated by acetate anions and able to
catch protons similar to above mentioned mononuclear complexes
(Scheme 1) [9].
(153 cmꢁ1) illustrates the bidentate coordination mode of carboxy-
lato group. In addition, the characteristic vibration absorption
peaks of C@N bonds in the macrocycle and ClOꢁ4 are observed at
1642 and 1091, 624 cmꢁ1, respectively. The structure of the title
complex is quite different from previous analogous macrocyclic
complexes [11]. On the one hand, two manganese ions, bridged
by one phenolate oxygen and two carboxylates, are located in
the half of the chamber formed by the ligand L. On the other hand,
each of the imino-N atoms in other half of the chamber catches a
proton similar to the previous mononuclear macrocyclic com-
plexes [8,12], which is the first example of recognizing proton by
dinuclear complex.
Selected bond lengths [Å] and angles [°]: Mn1–O1 2.134(2),
Mn1–O3 2.110(2), Mn1–O5 2.203(2), Mn1–N1 2.234(2), Mn1–N3
2.383(3), Mn1–N5 2.274(2), Mn2–O1 2.092(2), Mn2–O4 2.144(2),
Mn2–O6 2.116(2), Mn2–N2 2.247(2), Mn2–N4 2.322(2), Mn–N6
2.312(3), O1–Mn1–O3 102.77(8), O1–Mn1–N3 155..32(8), O3–
Mn1–N3 95.88(8), O1–Mn1–N5 90.93(9), N3–Mn1–N5 73.50(9),
O5–Mn1–O1 90.17(8), O5–Mn1–O3 86.00(8), O5–Mn1–N3
98.12(9), O5–Mn1–N5 84.04(9), N1–Mn1–O5 175.41(9), O1–
Mn2–O6 94.32(8), O1–Mn2–N4 169.43(8), O6–Mn2–N4 94.69(9),
O1–Mn2–N6 96.22(8), O6–Mn2–N6 167.86(8), N4–Mn2–N6
74.28(9), O4–Mn2–O1 98.92(7), O4–Mn2–O6 93.17(8), O4–Mn2–
N4 86.08(8), O4–Mn2–N6 91.15(8), N2–Mn2–O4 177.76(9).
Each Mn(II) is coordinated with an N3O3 unit composed of one
Oph, two OOAc from two 1,3-bridged acetate ions, one imine N and
two N from ligating pendant-arm. The coordination configuration
about Mn1 can be described as a highly distorted octahedron with
O3, O5, N5, N1 in the equatorial plane (the mean deviation of
The X-ray single crystal diffraction analysis indicates that the ti-
tle dinuclear complex contains one [Mn2II(H2L)( -OAc)2]2+, two
l
perchlorate counter anions and one solvent water molecule [10]
(Fig. 1). The structural characters of the title complex are also con-
firmed by its IR spectrum. The two peaks at 1591 and 1438 cmꢁ1
indicate the presence of carboxylato groups. The small
Dm value
* Corresponding author. Address: Key Laboratory for Green Chemical Process of
Ministry of Education, School of Chemical Engineering and Pharmacy, Wuhan
Institute of Technology, Wuhan 430073, PR China. Tel.: +86 27 8719 4465.
E-mail address: zhiqpan@163.com (Z.-Q. Pan).
1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2008.09.001

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Z.-Q. Pan et al. / Inorganic Chemistry Communications 11 (2008) 1363–1366
Scheme 1. The routine of the synthesis of [Mn2II(H2L)(
l-OAc)2](ClO4)2 ꢀ H2O.
0.1232 Å) and O1, N3 in the axial sites (the bond angle of O1–Mn1–
N3 is 155.3(1)°). The Mn2, for which O4, O6, N2, N6 comprise the
equatorial plane (the mean deviation of 0.0873 Å) and O1, N4 occu-
py the axial sites (the bond angles of O4–Mn2–N2 is 177.1(1)°),
respectively, exhibits more regular geometry of octahedron than
that of Mn1. The Mn1ꢀ ꢀ ꢀMn2 separation is 3.401(2) Å.
The two acetate groups are asymmetrically bridging as evi-
denced by the Mn–OOAc, for the Mn1–O5(2.203(2) Å) and Mn2–
O4 (2.144(2) Å) distances are longer than those of the Mn1–O3
(2.110 (2) Å) and Mn2–O6 (2.116(2) Å), respectively, and the situ-
ation of the phenoxy oxygen distances are similar to above for
Mn1–O1 bond (2.134(2) Å) distance is longer than that of Mn1–
O2 (2.092(2) Å). The Mn–O bond length is in the usual range ob-
served for Mn(II) complexes [13]. Two pyridine groups of pendant
arms, trans to each other, coordinate to two metal ions with the
Mn–Npy bond lengths Mn1–N5 2.274(2) and Mn2–N6 2.312(3) Å,
respectively, which are slightly longer than those of the Mn–Nim
(Mn1–N1 2.234(2) Å, Mn2–N2 2.247(2) Å). Additionally, the lon-
gest bond is the Mn–Nter (Mn1–N3 2.383(3) Å, Mn2–N4
2.322(2) Å). The Mn–N bond distances all fall within the range of
MnII–N bonds reported previously. [13,11b,c].
Elemental analysis is hard to ensure exactly number of hydro-
gen atoms because it is so light and X-ray determination of com-
plexes is difficult to ascertain charges of metal ions rigorously for
existence of rudimental electron. It is an effective method to ex-
plore the charges of metal ions by analyzing the magnetic interac-
tions between metal ions in the complexes. Variable-temperature
magnetic susceptibility data were recorded for the complex in
the temperature range 2–300 K. No significant field dependence
of the magnetic susceptibility (
vm) was observed. The plot of
v
mT against temperature is shown in Fig. 2.
v
mT decreases smoothly from 8.08 cm3 K molꢁ1 at 300 K to
6.14 cm3 K molꢁ1 at 100 K and then more abruptly to reach
0.05 cm3 K molꢁ1 at 2 K. This behavior, which is very similar to that
of the dimanganese(II) complex in the literature [14a], is character-
Fig. 1. Perspective view of the cation [Mn2II(H2L)( -OAc)2]2+ with thermal
l
ellipsoids shown at 30%.

Z.-Q. Pan et al. / Inorganic Chemistry Communications 11 (2008) 1363–1366
1365
8
6
4
2
0
T
0
50
100
150
T
200
250
300
Fig. 3. Cyclic voltammogram of [Mn2II(H2L)(
l
-OAc)2](ClO4)2 ꢀ H2O in DMF
Fig. 2. Experimental and calculated plots of
with Eq. (1).
vmT vs. T. The solid line shows the fit
(5 ꢂ 10ꢁ4 mol Lꢁ1) containing 0.1 mol Lꢁ1 NBu4ClO4 on a glassy carbon electrode
at a scan rate of 20 mV Sꢁ1
.
istic of two high-spin (S = 5/2) Mn(II) ions experiencing a moderate
antiferromagnetic coupling. The magnetic data could be accounted
for by the Van Vleck equation for two spins S = 5/2.
For comparison, the similar experiment was carried out in
CH3CN under the same conditions; the oxygen evolution in CH3CN
2Nb2g2 expð2xÞ þ 5 expð6xÞ þ 14 expð12xÞ þ 30 expð20xÞ þ 55 expð30xÞ
kT 1 þ 3 expð2xÞ þ 5 expð6xÞ þ 7 expð12xÞ þ 9 expð20xÞ þ 11 expð30xÞ
vm
¼
þ 2t
ð1Þ
where x = J/kT, N, g, b, k and T have their usual meanings and t is the
temperature-independent paramagnetism. g was fixed to 2 in the
calculations. The best least-squares fit of the experimental data
was observed without lag time. The initial rate of liberation dioxy-
gen is much lower than that of [Mn2IIL](ClO4)2[11b], but the rate
significantly increased with the enhancement of the time. The per-
centage of disproportionation of H2O2 into H2O and O2 catalyzed by
present complex is higher than that by [Mn2IIL](ClO4)2. Meanwhile,
the efficiency of disproportionation of H2O2 catalyzed by title com-
plex in CH3CN is much higher than that in DMF. Furthermore, the
molar conductivities of the complex in CH3OH, DMF and CH3CN are
400, 410 and 450 s cm2 molꢁ1, which are located in the range of
1:3 type electrolyte, and the UV spectra are slightly red shift in
the order. So, the ionization of acetate coordinated to metal is
were obtained with the parameters J = ꢁ3.733(7) cmꢁ1
,
t = 3.6(0) ꢂ 10ꢁ4cm3 molꢁ1 and R = 8.1 ꢂ 10ꢁ4 (R is an agreement
P
P
factor defined as ({ [(
v
mT)calc ꢁ (
v
mT)obs]2/
(v }
mT)o2bs 1/2), which
were agreement with the binuclear Mn(II) complexes with pheno-
late oxygen and 1,3-carboxylate bridging reported by previous
works (range of ꢁ2 to ꢁ10 cmꢁ1) [14]. The experiment data in the
range of 60ꢁ300 K are well approximated by a Curie–Weiss law with
the values of C = 9.727 and
H
= ꢁ59.54 K.
The results of the cyclic voltammogram experiment of the com-
plex were also agreement with electrochemical behaviors of dima-
ganese (II) complexes (Fig. 3) [15]. The complex displays two
quasi-reversible redox couples with the E1/2 of 0.3775 V and
0.8409 V, respectively, which can be attributed to the redox reac-
tion of MnIIMnII M MnIIMnIII and MnIIMnIII M MnIIIMnIII,
respectively. The E1/2 (1) value is similar to that of analogous
Mn2IIL(
l-OAc)2 complex, and quite bigger than that of the
mixed-value MnIIMnIII complexes (approximate to zero and even
to a negative).
The CAT-like activity of [Mn2II(H2L)(
l-OAc)2](ClO4)2 ꢀ H2O to
catalyze the disproportionation of H2O2 into H2O and O2 has been
investigated in DMF and CH3CN at 0 °C, respectively. The time
course of the O2-evolution by the compound is shown in Fig. 4.
In DMF, the initial rate was very low, but the rate significantly in-
creased after a lag time. The situation is similar to those of the
[Mn2IIL4,4(OAc)2] [16] and [Mn2IIL(PhCO2)2](NCS) [17]. However,
the present complex displays a longer lag time and a lower libera-
tion of dioxygen showed by the O2-evolution profile. The liberation
of dioxygen catalyzed by[Mn2II(H2L)(
l-OAc)2](ClO4)2 (60%
theoretical amount) is much lower than that catalyzed by
[Mn2IIL3,3(OAc)2] (100% theoretical amount), suggesting that the
dissociation of the bridging acetates is more difficult than that of
the relative ones in similar complexes [16].
Fig. 4. Time course of O2 evolution in the decomposition of H2O2 by [Mn2II(H2L)(
l-
OAc)2](ClO4)2. (a) Complex 1.2 mM in DMF (2 mL); H2O2 6 M in DMF (0.5 mL); and
(b) complex 1.2 mM in CH3CN (2 mL); H2O2 6 M in CH3CN (0.5 mL).

1366
Z.-Q. Pan et al. / Inorganic Chemistry Communications 11 (2008) 1363–1366
SHELXTL) using all unique data. Crystal Data for [Mn2IIL(
l-
easier in CH3CN solution than that in DMF solution, which is agree-
ment with the results of CAT-like activity in the solutions.
In summary, the binuclear crystal manganese (II) complex
acetato)2](ClO4)2 ꢀ H2O: C46H60Mn2N8O15Cl2, M = 1145.8. Orthorhombic, space
group Pna2(1), Z = 2, a = 14.414(2) Å, b = 14.786(2) Å, c = 15.006(2) Å,
a
= 110.372(3)°,
b = 99.179(3)°,
c
= 107.891(2)°,
V = 2722.9(6) Å3,
[Mn2II(H2L)(
l-OAc)2](ClO4)2 ꢀ H2O with an uncoordinating cavity
Dcaled = 1.395 g cmꢁ3
,
l(Mo-K
a
) = 0.632 mmꢁ1
,
T = 291 K. 15898 data
collected, 10517 independent refections (Rint = 0.0204). Final R1 = 0.0481,
wR2 = 0.1055 [I > 2 (I)]. CCDC Reference Number CCDC 619821.
caught two protons was obtained by the transmetalation reaction.
The complex has the CAT-like activity in DMF and CH3CN solution,
and the efficiency of disproportionation of H2O2 is largely depen-
dent on the property of solution.
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The Project was supported by the midlife and youth excellent
innovation group of Hubei Province, China (No. T200802), and
key foundation of the Education Department of Hubei Province,
China (No. D20081503).
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