A dinuclear copper(II) complex and a zigzag chain iron(II) polymer based on the 4-antipyrine derived Schiff base ligands: The hydroxylation and redox occurred under the solvothermal conditions

Article abstract of DOI:10.1016/j.inoche.2007.03.008

A new dinuclear copper(II) compound, [Cu₂(L1-O)₂] (1) (L1 = (4E)-4-(2-hydroxybenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one), and zigzag chain polymer, {[FeCl₂(L2)]}_n (2) (L2 = 1,5-dimethyl-2-phenyl-4-{[(1E)-pyridine-4-ylmethylene]amino}-1,2-dihydro-3H-pyrazol-3-one), were synthesized by solvothermal reactions and structurally characterized. The methyl group hydroxylation and the redox have been observed in the preparation of 1 and 2, respectively.

Full text of DOI:10.1016/j.inoche.2007.03.008

Inorganic Chemistry Communications 10 (2007) 709–712
www.elsevier.com/locate/inoche
A dinuclear copper(II) complex and a zigzag chain iron(II)
polymer based on the 4-antipyrine derived Schiff base ligands:
The hydroxylation and redox occurred under the solvothermal conditions
a,
a,b
Xian-Wen Wang *, Yue-Qing Zheng
a
Faculty of Material Science and Chemical Engineering, China University of Geoscience, Hubei, Wuhan 430074, China
The State Key Laboratory Base of Novel Functional Materials and Preparation Science, Faculty of Material Science and Chemical Engineering,
Ningbo University, Zhejiang, Ningbo 315211, China
b
Received 28 February 2007; accepted 8 March 2007
Available online 25 March 2007
Abstract
A new dinuclear copper(II) compound, [Cu2(L1-O)2] (1) (L1 = (4E)-4-(2-hydroxybenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-
phenylpyrazol-5-one), and zigzag chain polymer, {[FeCl2(L2)]}n (2) (L2 = 1,5-dimethyl-2-phenyl-4-{[(1E)-pyridine-4-ylmethyl-
ene]amino}-1,2-dihydro-3H-pyrazol-3-one), were synthesized by solvothermal reactions and structurally characterized. The methyl
group hydroxylation and the redox have been observed in the preparation of 1 and 2, respectively.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Dinuclear copper(II); Iron(II) polymer; Solvothermal synthese; Methyl group hydroxylation; Redox
Hydro(solvo)thermal synthesis has been widely employed
to generate MOFs with unique structures and special prop-
erties, whose reaction mechanism conforms to liquid nucle-
ation mode [1]. On the one hand, the hydrothermal
reactions are complicated and unpredictable, especially at
high-temperature, as the high-temperature water or solvents
can function as a reaction medium for some fantastic reac-
tions which are difficult to occur under ambient conditions
[2]. As a result, such reactions will assuredly enhance the dif-
ficulty of the purposeful material syntheses and rational
molecular design. On the other hand, they could also afford
some novel functional materials with enchanting structures.
It is well accepted that Cu(II) ions can be reduced to Cu(I) by
heterocyclic ligands under hydrothermal conditions [3].
Additionally, some unexpected reactions or so-called
in situ reactions, such as ligand oxidative coupling, hydroly-
sis, substitution, and the simultaneous reduction and substi-
tution, can also occur under hydrothermal conditions
mediated by transition metal salts [4].
Schiff base coordination complexes have attracted great
attention over the past decades due not only to their facile
syntheses, their wide application and the accessibility of
diverse structural modifications, but also to their biological
modeling applications, catalysis, design of molecular ferro
magnets and materials chemistry [5–10]. The Schiff bases of
4-aminoantipyrine and their coordination complexes have
been extensively investigated because of their biological,
clinical, pharmacological, analytical and material applica-
tions [11–13]. However, only a few structurally character-
ized metal complexes with 4-aminoantipyrine Schiff base
derived ligands have been reported, and its coordination
chemistry remains largely unexplored [14,15].
As part of our interest in the coordination chemistry of
the Schiff base derived from 4-aminoantipyrine, we noted
that, during the reaction of Cu(Ac)2 Æ H2O with (4E)-4-(2-
hydroxybenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-
phenylpyrazol-5-one (L1), as shown in Scheme 1, one of
the methyl group of L1 was involved in an hydroxylation
reaction leading to the compound, [Cu2(L1-O)2] 1.
Although the Cu2+ mediated simultaneous dehydrogena-
tive coupling and hydroxylation of the N-heterocyclic
*
Corresponding author. Fax: +86 27 87801763.
E-mail address: wxw10108092@yahoo.com.cn (X.-W. Wang).
1387-7003/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2007.03.008

710
X.-W. Wang, Y.-Q. Zheng / Inorganic Chemistry Communications 10 (2007) 709–712
Scheme 1.
ligands were reported, they occurred under hydrothermal
reactions with the temperature over 175 °C [16]. In our
case, the reactions occured only at 80 °C under solvother-
mal conditions. The reaction of FeCl3 with 1,5-dimethyl-
2-phenyl-4-{[(1E)-pyridine-4-ylmethylene]amino}-1,2-dihy-
dro-3H-pyrazol-3-one (L2) under solvothermal conditions
afforded [FeCl2(L2)] (2), where the initial Fe(III) ions have
been reduced to Fe(II) ions by the heterocyclic ligand.
Herein, we report the two isolated complexes, [Cu2(L1-
O)2] (1) and [FeCl2(L2)] (2).
The ligand L1 and L2 were synthesized as reported previ-
ously by the base condensation of 4-aminoantipyrine with
2-hydroxybenzaldehyde and pyridine-3-carboxaldehyde,
respectively, in a 1:1 molar ratio in ethanol at 80 °C for
2 h [17,18]. Dark blue cubic crystals and red rod-shaped
crystals for 1 and 2 were obtained under solvothermal con-
ditions and characterized by spectroscopic data1 as well as
X-ray crystallography.2 It is noteworthy that the formation
of 1 shows significant dependence on solvents and materials
molar ratio. We have also tentatively tried to obtain new
structure by altering the metal-to-ligand ratio, from 1:1,
2:1 to 3:1, unfortunately, and the complex 1 cannot be
generated. When using other copper(II) salts instead of
Cu(Ac)2 Æ H2O, complex 1 cannot be obtained either, show-
ing that the acetate anions also play a key role in the methyl
group hydroxylation due to its alkalescence. This indicates
that the products of 1 strictly depend on the metal-to-ligand
ratio and solvent system, and the hydroxylation substitution
reaction probably mediated by the Cu(Ac)2 Æ H2O. Compa-
rably, the reaction of FeCl3 Æ 4H2O with L2 yielded the
one-dimensional complex 2, since we obtained a two-dimen-
sional grid complex [FeCl2(L2)], only with FeCl2 Æ 4H2O
instead of FeCl3 Æ 4H2O under the same reaction condition
[19], where one chlorine atom acts as l2-bridge.
Complex 1 crystallizes in monoclinic space group C2/c.
1 is a dinuclear Cu(II) complex arranged around inversion
center (Fig. 1). Each ligand acts as a tri-chelate coordinat-
ing to the Cu atom by two O and one N atoms. The O
atom of the alcoholate group bridges two Cu atoms leading
to a Cu2O2 rhombic ring with a Cu–Cu separation of
1
Preparation of 1: A 25 ml Teflon-lined stainless steel autoclave was
˚
3.0138(11) A. Each Cu atom has a square-planar geometry.
charged with 0.752 g (4.0 mmol) Cu(Ac)2 Æ H2O, 0.309 g (1.0 mmol) L1,
18 ml CH3OH, 1 ml CH2Cl2 and 1 ml triethylamine and heated at 80 °C
for 168 h, then cooled to room temperature. Dark black cubic crystals
were obtained in 10% yield based on the initial L1 input. Anal. Calc. for
C36H30Cu2N6O6: C 56.12, H 3.90, O 12.47%; found: C 56.08, H 3.96, O
12.43%. IR (cmꢀ1): 2927w, 1625vs, 1597m, 1548m, 1491m, 1428m, 1368m,
1309m, 1325w, 1138w, 1058w, 1017w, 948w, 820w, 760w, , 698s, 625w,
566m, 530m cmꢀ1. Preparation of 2: A 25 ml Teflon-lined stainless steel
autoclave was charged with 0.290 g (1 mmol) FeCl3 Æ 4H2O, 0.260 g
(1 mmol) L2 and 18 ml CH3OH and heated at 80 °C for 168 h, then
cooled to room temperature. Red crystals were obtained in 60% yield
based on the initial FeCl3 Æ 4H2O input. Anal. Calc. for C17H16Cl2FeN4O
(%): C, 48.69; H, 3.82, N, 13.36 Found: C, 48.71; H, 3.90, N, 13.34. IR
(cmꢀ1): 2927w, 1617vs, 1599m, 1578vs, 1519m, 1491m, 1442m, 1428m,
1366m, 1276m, 1204w, 1171w, 1131w, 1056w, 1027w, 978w, 953w, 897w,
The four-membered Cu2O2 bridging unit in the dimer is
strictly planar due to crystallographic inversion symmetry.
Each Cu atom is chelated by the deprotonated tridentate
anion ligand into two six-membered rings, respectively.
˚
The Cu–O average bond length is 1.901(3) A, which is
slightly shorter than those observed in the square-planarly
coordinated binuclear Cu(II) complexes reported by Sinn
[20]. The C11–O2 bond distance is the representative bond
value for C–O single bond, and the other bond values of
the ligand are comparable to those of free molecule L1
[17]. A noteworthy feature of this compound is that the
ligand adopts a planar geometry except for the phenyl
group attached to pyrazolyl ring in the present compound,
forming a large p-conjugation system with the p-electron
cloud delocalizing over the whole ligand. In the crystal
structure, the title complex molecules are stabilized by p–
p stacking interactions between the large p-conjugation
system at (x,y,z) and the inversion center symmetric mole-
819w, 769m, 748w, 698s, 643w cmꢀ1
.
2
Crystal data for 1: M = 769.74, space group C2/c, a = 27.330(6),
3
˚
˚
b = 7.2758(10), c = 19.424(3) A, b = 124.543(11)°, V = 3181.5(9) A ,
F(000) = 1576, Z = 4, Dc = 1.607 g cmꢀ3, l = 1.396 mmꢀ1, R1 = 0.0585,
wR2 = 0.1151 with S = 1.018, and the largest peak and deepest hole in the
3
˚
final difference Fourier map are 0.421 and ꢀ0.340 e/A . Crystal data for 2:
M = 741.05, space group P21/n, a = 9.0951(11), b = 17.6726(15),
3
˚
˚
c = 12.3674(14) A, b = 109.155(10)°, V = 1877.8(3) A , F(000) = 856,
Z = 4, Dc = 1.482 g cmꢀ3, l = 1.100 mmꢀ1, R1 = 0.0462, wR2 = 0.0991
with S = 1.011, and the largest peak and deepest hole in the final difference
1
cules at position ð ꢀ x; 32 ꢀ y; 1 ꢀ zÞ into ladder-like chain
2
along [010] direction, with the perpendicular contacts of
3
˚
˚
Fourier map are 0.504 and ꢀ0.418 e/A .
3.342(7) A.

X.-W. Wang, Y.-Q. Zheng / Inorganic Chemistry Communications 10 (2007) 709–712
711
˚
˚
(2.008(2) A) and Fe–N bond distance (2.101(2) A) are also
comparable to those of the related complexes [21,22].
Although significantly intriguing magnetic properties
may exist in the complex 1, we failed to carry out the
relevant magnetic experiments because of the low yield
and the impurity of the crystalline product. The magnetic
susceptibilities of 2 were measured using a SQUID magne-
tometer on crystalline samples in the temperature range of
1.8 K to 300 K under 2 kOe to confirm the charge value of
the iron atoms. The temperature dependence of vmT and
vm for complex 2 is plotted in Fig. 3. The vmT product of
3.27 cm3 K molꢀ1 at 300 K is close to the typical value
for magnetically dilute, high-spin Fe(II) ion with g > 2.0
[23]. The value of vmT increases gradually to a maximum
of approximately 3.37 cm3 K molꢀ1 at 90 K, then decreases
sharply to a value of approximately 2.03 cm3 K molꢀ1 at
1.8 K. The vm vs T curve starts from 0.01 cm3 molꢀ1
at 300 K and increases monotonically to 1.13 cm3 molꢀ1
at 1.8 K. The shape of the vmT curve (300–90 K) is clearly
Fig. 1. The molecule of the title compound (I), showing the atom-labelling
scheme. Displacement ellipsoids are drawn at the 60% probability level.
˚
Selected bond lengths (A) and angles (°): Cu1–O1 1.866(3), Cu1–O2
1.892(3), Cu1–O2i 1.945(3), Cu1–N1 1.953(3), Cu1–Cu1i 3.0138(11), C11–
O2 1.395(5); O1–Cu1–N1 96.40(14), O2–Cu1–N1 96.83(14). Symmetry
1
code: (i) ꢀ x; 12 ꢀ y; 1 ꢀ z.
2
Complex 2 crystallizes in the monoclinic unit cell space
group P21/n. As shown in Fig. 2, the iron(II) atoms are
ꢀ
bridged by L2 into a zigzag chain along ½101ꢁ direction.
Each L2 acts as bidentate bridging spacer through the
pyridyl N atom and the pyrazole O atom bounded to the
Fe(II) atom. Each one of the four-coordinated Fe(II)
atoms exhibits a significantly distorted tetrahedral geome-
try with the bond angles ranging from 89.75(9) to
˚
120.03(8)°. The Fe–Cl1 bond length (2.2317(11) A) is
slightly shorter than the Fe–Cl2 bond length
˚
(2.2617(10) A), and both of them are similar to those of
Fig. 3. Temperature variation of magnetic susceptibility vs temperature
the related Fe(II) complexes [21]. The Fe–O bond distances
for 2.
˚
Fig. 2. The zigzag chain diagram along [101] direction showing the polymeric structure of 2. Selected bond lengths (A) and angles (°): Fe1–O 2.009(2),
Fe1–N1 2.102(2), Fe1–Cl1 2.2314(10), Fe1–Cl2 2.2615(10); O1–Fe1–N1i 89.78(9), O1–Fe1–Cl1 112.95(7); N1i–Fe1–Cl1 120.04(8), O1–Fe1–Cl2 114.69(7),
N1i–Fe1–Cl2 102.81(7), Cl1–Fe1–Cl2 114.17(4). Symmetry code: (i) þ x; ꢀ y; þ z.
1
1
1
2
2
2

712
X.-W. Wang, Y.-Q. Zheng / Inorganic Chemistry Communications 10 (2007) 709–712
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indicative of no magnetic interaction. The low temperature
data shows significant zero-field splitting of the single iro-
n(II) ion ground-state [24].
In summary, a new dinuclear copper(II) compound,
[Cu2(L1-O)2] (1) and a zigzag chain polymer, {[FeCl2(L2)]}n
(2) have been synthesized by solvothermal reactions
and structurally characterized. The methyl group hydroxyl-
ation and the redox have been observed in the preparation of
1 and 2, respectively. This work may provide useful informa-
tion for investigations of hydro(solvo)thermal reaction
mechanism.
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CCDC 639042 and 639043 contain the supplementary
crystallographic data for the complexes 1 and 2. These data
can be obtained free of charge via http://www.ccdc.cam.
ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
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Acknowledgments
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Angew. Chem. Int. Ed. 44 (2005) 5471.
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[19] X.-W. Wang, Assembly, Characterization and Properties Study of
Metal Coordination Polymers Bridged by Schiff base Derived from
Pyridine-3(4)-carboxaldehyde and 4-aminoantipyrine or by Drug
Chiniofon Ligand, MSC Thesis, 2004.
The project was supported by the Expert Project of Key
Basic Research of the Ministry of Science and Technology
of China (2003CCA00800), the Zhejiang Provincial
Natural Science Foundation (Z203067), Ningbo Municipal
Natural Science Foundation (2006A610061), and the Sci-
entific Research Fund of Ningbo University (XK200459,
SS2004033).
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