The construction of versatile azido-bridged Schiff base Copper(II) complexes with xanthine oxidase inhibitory activity

Article abstract of DOI:10.1007/s11224-012-9956-7

Three new versatile azido-bridged Schiff base Copper(II) complexes, [Cu₂(L¹)₂(μ_1.1-N ₃)₂].2CH₃OH (1), [Cu(L²)(μ _1.3-N₃)]ⁿ (2), and [Cu

Full text of DOI:10.1007/s11224-012-9956-7

Struct Chem (2012) 23:1489–1496
DOI 10.1007/s11224-012-9956-7
ORIGINAL RESEARCH
The construction of versatile azido-bridged Schiff base Copper(II)
complexes with xanthine oxidase inhibitory activity
•
Mei Zhang Dong-Mei Xian Na Zhang
•
•
•
Hai-Hua Li Zhong-Lu You
Received: 2 November 2011 / Accepted: 24 January 2012 / Published online: 11 February 2012
Ó Springer Science+Business Media, LLC 2012
Abstract Three new versatile azido-bridged Schiff base
Copper(II) complexes, [Cu2(L1)2(l1,1-N3)2]Á2CH3OH (1),
[Cu(L2)(l1,3-N3)]n (2), and [Cu2(L3)(l1,1-N3)2(N3)]2 (3),
where L1, L2, and L3 are the deprotonated form of the Schiff
bases 5-diethylamino-2-[(2-isopropylaminoethylimino)methyl]
phenol (HL1), 5-methoxy-2-[(2-morpholin-4-ylethylimino)
methyl]phenol (HL2), and 5-methoxy-2-[(2-piperidin-1-
ylethylimino)methyl]phenol (HL3), respectively, have been
prepared and structurally characterized by elemental anal-
ysis, IR spectra, and single-crystal X-ray crystallography.
Complex 1 is a crystallographic centro-symmetric end-on
azido-bridged dinuclear Copper(II) compound, with the
Keywords Schiff base Á Cu complex Á Polynuclear
complex Á Azide Á Crystal structure Á Xanthine oxidase Á
CuÁÁÁCu interaction
Introduction
Polymeric complexes with bridging groups are currently
attracting much attention for their interesting structures and
wide applications [1–3]. The Schiff bases derived from
salicylaldehyde and its derivatives are a kind of versatile
ligands in coordination chemistry. The rational design and
construction of polymeric complexes with Schiff bases are
of particular interest in coordination and structural chem-
istry. Although many bridging groups and metal ions have
been employed for the construction of polymeric com-
plexes, the Copper-azide system is one of the most popular
among them [4–6]. A number of azido-bridged Copper
complexes have been reported [7–11], however, the search
in the Cambridge Crystallographic Database (CSD; version
5.32 with addenda up to May 2011) [12] has revealed that
only 74 azido-bridged polynuclear Copper complexes with
Schiff bases derived from salicylaldehyde and its deriva-
tives have been reported. Recently, we found that the
Schiff base Copper complexes have xanthine oxidase (XO)
inhibitory activity [13]. In order to enrich the azido-bridged
Schiff base Copper(II) complexes, as well as further
investigate the XO inhibitory activity, in this article, three
new polymeric complexes, [Cu2(L1)2(l1,1-N3)2]Á2CH3OH
(1), [Cu(L2)(l1,3-N3)]n (2), and [Cu2(L3)(l1,1-N3)2(N3)]2
(3), where L1, L2, and L3 are the deprotonated form of the
Schiff bases 5-diethylamino-2-[(2-isopropylaminoethylimino)
methyl]phenol (HL1), 5-methoxy-2-[(2-morpholin-4-yleth-
ylimino)methyl]phenol (HL2), and 5-methoxy-2-[(2-pip-
eridin-1-ylethylimino)methyl]phenol (HL3) (Scheme 1),
˚
CuÁÁÁCu distance of 3.512(1) A. Complex 2 is an end-to-end
azido-bridged polymeric Copper(II) compound, with the
˚
CuÁÁÁCu distance of 5.716(2) A. Complex 3 is a phenolato-O
and end-on azido-bridged tetranuclear Copper(II) com-
pound, with the CuÁÁÁCu distances of 3.122(1) and
˚
3.108(1) A. The Cu atoms in 1 and 2, and the inner two Cu
atoms in 3 are in square-pyramidal coordination. The outer
two Cu atoms in 3 are in square planar coordination. The
azide ligands are dramatic bridging groups for the con-
struction of versatile polynuclear Copper complexes with
Schiff bases. The xanthine oxidase inhibitory activity of the
complexes was evaluated.
Electronic supplementary material The online version of this
article (doi:10.1007/s11224-012-9956-7) contains supplementary
material, which is available to authorized users.
M. Zhang Á D.-M. Xian Á N. Zhang Á H.-H. Li Á Z.-L. You (&)
Department of Chemistry and Chemical Engineering, Liaoning
Normal University, Dalian 116029, People’s Republic of China
e-mail: youzhonglu@yahoo.com.cn
123

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Struct Chem (2012) 23:1489–1496
Synthesis of [Cu2(L1)2(l1,1-N3)2]Á2CH3OH (1)
respectively, were prepared and evaluated for their XO
inhibitory activity.
To the methanolic solution (10 mL) of HL1 (0.028 g,
0.1 mmol) was added a methanolic solution (10 mL) of
CuCl2Á2H2O (0.017 g, 0.1 mmol) and sodium azide
(0.012 g, 0.2 mmol) with stirring. The mixture was stirred
for 30 min at room temperature to give a deep blue solution.
After keeping the solution in air for a few days, blue block-
shaped crystals of 1, suitable for X-ray crystal structural
determination, were formed at the bottom of the vessel on
slow evaporation of the solvent. The crystals were isolated,
washed three times with methanol and dried in air. Yield
45%. IR data (cm-1): 3248 (sh, w), 2036 (s), 1599 (s), 1510
(m), 1407 (w), 1334 (m), 1248 (m), 1141 (m), 1077 (w), 1012
(w), 827 (w), 777 (m), 700 (w), 633 (w), 576 (w), 538 (w),
447 (w). Anal. calc. for C34H60Cu2N12O4: C, 49.3; H, 7.3; N,
20.3; found: C, 49.1; H, 7.5; N, 20.1%.
Experimental
Materials and measurements
Starting materials, reagents and solvents with AR grade
were purchased from commercial suppliers and were used
without further purification. Elemental analyses were per-
formed on a Perkin-Elmer 240C elemental analyzer. The
IR spectra were recorded on a Jasco FT/IR-4000 spec-
trometer as KBr pellets in the 400–4,000 cm-1 region.
Single-crystal structural X-ray diffraction was carried out
on a Bruker SMART 1000 CCD area diffractometer. Molar
conductivities of the complexes were measured at 25 °C
with a DDS-11 molar conductor.
Synthesis of [Cu(L2)(l1,3-N3)]n (2)
Caution Sodium azide is potentially explosive, only
small quantity should be used and handled with great care.
Complex 2 was synthesized by the similar method as that
described for 1, with HL1 replaced by HL2 (0.026 g,
0.1 mmol). The blue block-shaped single crystals of 2 were
isolated, washed three times with methanol and dried in air.
Yield 61%. IR data (cm-1): 3366 (sh, w), 2043 (s), 1633
(s), 1604 (s), 1530 (m), 1461 (m), 1433 (m), 1319 (w),
1239 (m), 1170 (m), 1137 (m), 1027 (w), 931 (w), 851 (m),
754 (w), 646 (w), 583 (w), 554 (w), 475 (w). Anal. calc. for
C14H19CuN5O3: C, 45.6; H, 5.2; N, 19.0; found: C, 45.4; H,
5.3; N, 18.9%.
Synthesis of the Schiff bases
The Schiff bases were synthesized by the same method as
described here. To the methanolic solution (50 mL) of the
carbonyl-containing compounds (1.0 mmol each) was
added a methanolic solution (50 mL) of amines (1.0 mmol
each) with stirring. The mixtures were stirred for 30 min at
room temperature to give yellow solution. The solvent was
evaporated to give yellow gummy product of the Schiff
bases.
Synthesis of [Cu2(L3)(l1,1-N3)2(N3)]2 (3)
For HL1: yield 79%. Characteristic IR data: 1,616 cm-1
.
Anal. calc. for C16H27N3O: C, 69.3; H, 9.8; N, 15.2; found:
C, 69.1; H, 9.9; N, 15.3%. For HL2: yield 83%. Charac-
teristic IR data: 1,613 cm-1. Anal. calc. for C14H20N2O3:
C, 63.6; H, 7.6; N, 10.6; found: C, 63.5; H, 7.6; N, 10.5%.
Complex 3 was synthesized by the similar method as that
described for 1, with HL1 replaced by HL3 (0.026 g,
0.1 mmol), and with CuCl2Á2H2O replaced by Cu(NO3)2Á
3H2O (0.024 g, 0.1 mmol). The blue block-shaped single
crystals of 3 were isolated, washed three times with methanol
and dried in air. Yield 27%. IR data (cm-1): 3446 (br, m),
2085 (s), 2068 (s), 2044 (s), 1627 (s), 1610 (s), 1532 (m),
1440 (m), 1286 (m), 1223 (s), 1169 (m), 1123 (m), 1027 (w),
977 (w), 853 (m), 755 (w), 638 (w), 577 (w), 561 (w), 473
(w). Anal. calc. for C15H21Cu2N11O2: C, 35.0; H, 4.1; N,
29.9; found: C, 35.1; H, 4.1; N, 29.7%.
For HL3: yield 76%. Characteristic IR data: 1,613 cm-1
.
Anal. calc. for C15H22N2O2: C, 68.7; H, 8.4; N, 10.7;
found: C, 68.5; H, 8.5; N, 10.6%.
H
O
N
N
N
N
N
OH
O
OH
HL1
HL2
X-ray data collection and structure determination
N
Diffraction intensities for the complexes were collected at
298(2) K using a Bruker SMART 1000 CCD area-detector
N
O
OH
˚
diffractometer with MoKa radiation (k = 0.71073 A). The
collected data were reduced with the SAINT program [14],
and multi-scan absorption correction was performed using
the SADABS program [15]. The structures were solved by
HL3
Scheme 1 The Schiff bases
123

Struct Chem (2012) 23:1489–1496
1491
direct methods. The complexes were refined against F2 by
full-matrix least-squares method using the SHELXTL
package [16]. All of the non-hydrogen atoms were refined
anisotropically. The amino H atom in 1 was located from a
difference Fourier map and refined isotropically, with N–H
200 lL of 84.8 lg/mL xanthine in 50 mM K2HPO4. The
reaction was started by addition of 66 lL 37.7 mU/mL
XO. The reaction was monitored for 6 min at 295 nm and
the product is expressed as lmol uric acid per minute. The
kinetics of the reactions were linear during the 6 min of
monitoring. The test compounds dissolved initially in
DMSO were incorporated in the enzyme assay to assess
their inhibitory activity at different concentrations, in
comparison with allopurinol as the standard reference. The
final concentration of DMSO in the assay was 5%. Control
experiments showed that DMSO, at a final concentration of
5%, did not affect the enzyme assay. XO inhibitory activity
was expressed as the percentage inhibition of XO in the
above assay mixture system or as the concentration
resulting in half-maximal enzyme velocity (IC50).
˚
distance restrained to 0.90(1) A. The remaining hydrogen
atoms were placed in calculated positions and constrained
to ride on their parent atoms. The crystallographic data for
the complexes are summarized in Table 1. Selected bond
lengths and angles are given in Table 2.
XO inhibitory test
The XO inhibition test was carried out in triplicate. Xan-
thine oxidase from cow’s milk was purchased from Sigma-
Aldrich (St. Louis, MO, USA). The XO activities with
xanthine as the substrate were measured spectrophoto-
metrically, based on the procedure reported by Kong et al.
[17], with modification. The activity of XO was measured
by uric acid formation monitored at 295 nm. The assay was
performed in a final volume of 1 mL 50 mM K2HPO4 pH
7.8 in a quartz cuvette. The reaction mixture contained
Results and discussion
The Schiff bases HL1, HL2, and HL3 were synthesized
by the reaction of equimolar quantities of 4-diethyl-
aminosalicylaldehyde with N-isopropylethane-1,2-diamine,
Table 1 Crystallographic data
Complex
1
2
3
for complexes
Formula
C34H60Cu2N12O4
828.0
C14H19CuN5O3
368.9
C15H21Cu2N11O2
514.5
Mr
T (K)
298(2)
298(2)
298(2)
Crystal shape/color
Crystal size (mm3)
Crystal system
Space group
Block/blue
0.21 9 0.18 9 0.17
Monoclinic
P21/c
Block/blue
0.20 9 0.20 9 0.18
Orthorhombic
P212121
9.658(3)
6.877(2)
23.201(3)
90
Block/blue
0.20 9 0.20 9 0.18
Triclinic
P-1
˚
a (A)
13.231(3)
13.802(3)
11.834(2)
90
8.3552(2)
9.7810(2)
12.7226(3)
97.1360(10)
91.7410(10)
103.9940(10)
999.07(4)
2
˚
b (A)
˚
c (A)
a (8)
b (8)
c (8)
105.510(2)
90
90
90
3
˚
V (A )
2082.3(7)
2
1541.0(7)
4
Z
Dc (g cm-3
)
1.321
1.590
1.710
l (Mo-Ka) (mm-1
)
1.071
1.440
2.167
F(000)
876
764
524
Independent reflections
Observed reflections (I C 2r(I))
Min. and max. transmission
Parameters
4543
3362
4179
3128
2919
3521
0.806 and 0.839
244
0.762 and 0.782
209
0.671 and 0.696
272
Restraints
1
0
0
Goodness-of-fit on F2
R1, wR2 [I C 2r(I)]a
R1, wR2 (all data)a
1.016
1.065
1.031
a
R1 = Fo-Fc/Fo,
wR2 = [ w(F2o-F2c)/
0.0383, 0.0950
0.0689, 0.1112
0.0321, 0.0736
0.0400, 0.0762
0.0278, 0.0692
0.0364, 0.0743
P
P
w(F2o)2]1/2
123

1492
Struct Chem (2012) 23:1489–1496
˚
Crystal structure description of 1
Table 2 Selected bond lengths/A and angles/° for the complexes
1
The single-crystal X-ray diffraction shows that the com-
pound 1 contains an end-on azido-bridged dinuclear
Copper(II) complex molecule (Fig. 1) and two methanol
molecules of crystallization. The asymmetric unit of the
complex contains one half of the molecule with the other half
generated by the inversion symmetry. The CuÁÁÁCu distance
Cu1–O1
1.942(2)
2.064(2)
2.479(2)
92.1(1)
92.3(1)
156.9(1)
95.2(1)
76.8(1)
Cu1–N1
Cu1–N4
1.937(2)
1.988(2)
Cu1–N2
Cu1–N4A
N1–Cu1–O1
O1–Cu1–N4
O1–Cu1–N2
N1–Cu1–N4A
N4–Cu1–N4A
2
N1–Cu1–N4
N1–Cu1–N2
N4–Cu1–N2
O1–Cu1–N4A
N2–Cu1–N4A
171.9(1)
83.4(1)
95.2(1)
110.7(1)
92.2(1)
˚
is 3.512(1) A, indicating there exists strong metallophilic
interactions. Each Cu atom in the complex is in a square-
pyramidal coordination, with the NNO donor set of the
Schiff base ligand and the N4 atom of the azide ligand
defining the basal plane, and with the N4i atom [symmetry
code for (i): -x, -y, 1 - z] of the other azide ligand occu-
pying the apical position. The deviation of the Cu atom from
the least-squares plane defined by the basal donor atoms is
Cu1–O1
1.897(2)
2.085(2)
2.847(2)
93.2(1)
170.6(1)
84.7(1)
96.8(1)
85.6(1)
Cu1–N1
Cu1–N3
1.932(2)
1.965(2)
Cu1–N2
Cu1–N5A
O1–Cu1–N1
N1–Cu1–N3
N1–Cu1–N2
O1–Cu1–N5A
N2–Cu1–N5A
3
O1–Cu1–N3
O1–Cu1–N2
N3–Cu1–N2
N1–Cu1–N5A
N3–Cu1–N5A
90.8(1)
176.6(1)
90.8(1)
82.5(1)
105.5(1)
˚
0.128(2) A. The azide ligands ligate two different but sym-
metry-related Cu atoms through the end-on bridging mode.
Significant distortion of the square pyramid is revealed by
bond lengths and angles between the apical and basal donor
atoms. The apical Cu–N bond length is much longer than
usual; the other bond lengths are within normal ranges and
comparable to the corresponding values observed in other
Schiff base Copper(II) complexes [18–20]. The bridging
azide groups are nearly linear and show bent coordination
with Cu atoms [N4–N5–N6 = 178.2(3)°, Cu1–N4–N5 =
128.3(2)°, Cu1i–N4–N5 = 126.6(2)°].
Cu1–O1
2.333(2)
1.941(2)
2.040(2)
1.934(2)
2.058(2)
156.5(1)
96.5(1)
Cu1–N3
Cu1–N9A
Cu2–O1
Cu2–N3
2.016(2)
2.014(2)
1.915(2)
2.016(2)
Cu1–N6
Cu1–N9
Cu2–N1
Cu2–N2
N6–Cu1–N9A
N9–Cu1–N3A
N9–Cu1–N9A
N6–Cu1–O1
N3–Cu1–O1
O1–Cu2–N1
N1–Cu2–N3
N1–Cu2–N2
N6–Cu1–N3
N6–Cu1–N9
N3vCu1–N9
N9–Cu1–O1A
N9–Cu1–O1
O1–Cu2–N3
O1–Cu2–N2
N3–Cu2–N2
93.8(1)
90.1(1)
176.0(1)
91.9(1)
105.1(1)
83.1(1)
168.7(1)
97.4(1)
In the crystal structure of the complex, the methanol
molecules are linked to the dinuclear Copper complex
molecule through intermolecular N2–H2AÁÁÁO2ii [N2–H2A =
79.9(1)
111.3(1)
73.3(1)
ii
ii
˚
˚
˚
0.90(1) A, H2AÁÁÁO2 = 2.07(2) A, N2ÁÁÁO2 = 2.951(4) A,
N2–H2AÁÁÁO2ii = 165(3)°, symmetry code for (ii): -x, 1 - y,
93.4(1)
1 - z], and O2–H2ÁÁÁO1iii [O2–H2 = 0.82 A, H2ÁÁÁO1 =
iii
˚
171.6(1)
84.5(1)
1.88 A, O2ÁÁÁO1 = 2.696(3) A, O2–H2ÁÁÁO1iii = 171°,
iii
˚
˚
symmetry code for iii): x, 1 ? y, z] hydrogen bonds (Fig. 2).
Compound 1 Symmetry code for A: -x, -y, 1 - z; Compound 2
Symmetry code for A: –1/2 ? x, -1/2 - y, -z; Compound 3
Symmetry code for A: -x, 1 - y, 1 - z
Crystal structure description of 2
4-methoxysalicylaldehyde with 2-morpholin-4-ylethylamine,
and 4-methoxysalicylaldehyde with 2-piperidin-1-ylethyl-
amine, respectively, in methanol. The air-stable yellow
gummy product of the Schiff bases is soluble in DMSO,
DMF, methanol, ethanol, acetonitrile, and chloroform. The
elemental analyses are in good agreement with the chemical
formulae proposed for the compounds. The three complexes
were synthesized by the reaction of the Schiff bases, Copper
salts, and sodium azide in methanol at ambient condition
(Scheme 2). All the complexes are stable in air at room
temperature for at least 2 months. The molar conductivities of
1, 2, and 3 at concentrations of 10-3 M are 11, 8, and
17 X-1 cm2 mol-1, respectively, indicate that the azide
groups in the complexes are coordinated to the metal center
and are not dissociated in solution.
The single-crystal X-ray diffraction shows that the com-
plex 2 is an end-to-end azido-bridged polymeric Copper(II)
complex (Fig. 3). The asymmetric unit of the complex
contains two [CuL2(l1,3-N3)] moieties. The CuÁÁÁCu dis-
˚
tance is 5.716(1) A, which is much longer than that in 1.
This is caused by the different bridging modes of the azide
ligands. Each Cu is in a square-pyramidal coordination,
with the NNO donor set of the Schiff base ligand and the
terminal N3 atom of a bridging azide ligand defining the
basal plane, and with the N5iv atom [symmetry code for
iv): -x, -y, 1 - z] of another azide ligand occupying the
apical position. The deviation of the Cu atom from the
least-squares plane defined by the basal donor atoms is
˚
0.097(2) A. The azide ligands ligate two different but
symmetry-related Cu atoms through the end-to-end
123

Struct Chem (2012) 23:1489–1496
1493
Scheme 2 The molecular
structures of the complexes
O
N
N
Cu
N
O
N
O
N
N
N
H
Cu
NEt2
N
N
OMe
MeO
NNN
O
Cu
NNN
O
N
Cu
NEt2
N
H
O
N
N
N
(2)
(1)
N
MeO
N
N
O
Cu
N
N
N
N
N
N
N
Cu
N
N
N
Cu
N
N
N
N
N
N
Cu
N
N
O
N
OMe
(3)
In the crystal structure of the complex, the molecules are
linked through bridging azide groups, forming polymeric
chains running along the a axis (Fig. 4).
Crystal structure description of 3
The single-crystal X-ray diffraction shows that the complex
3 is a phenolato-O and end-on azido-bridged tetranuclear
Copper(II) complex (Fig. 5). The asymmetric unit of the
complex contains one half of the molecule, with the other
half generated by the inversion symmetry. The CuÁÁÁCu
˚
distances are found to be 3.122(2) A for Cu1 and Cu2, and
Fig. 1 A perspective view of the molecular structure of 1 with the
atom labeling scheme. The thermal ellipsoids are drawn at the 30%
probability level. Atoms labeled with the suffix A or unlabeled are at
the symmetry position -x, -y, 1 - z. The two methanol molecules
were omitted for clarity
ii
3.108(2) A for Cu1 and Cu1 , indicating there exist strong
˚
metallophilic interactions. Each asymmetric unit is a dinu-
clear Copper(II) complex moiety, within which the Cu
atoms are connected by two bridging groups: one phenolate
O atom, and one l1,1-N3 ligand. The two asymmetric units
are further linked through another two l1,1-N3 ligands,
forming a tetranuclear complex. Each of the symmetry-
related two outermost Cu atoms is four-coordinated by the
NNO donor set of the Schiff base ligand and the N3 atom of
an azide ligand, forming a square planar coordination. The
Cu2 atom deviates from the least-squares plane defined by
bridging mode. Significant distortion of the square pyramid
is revealed by bond lengths and angles between the apical
and basal donor atoms. The apical Cu–N bond length is
much longer than usual; the other bond lengths are within
normal ranges and comparable to the corresponding values
observed in 1 and other Schiff base Copper(II) complexes
[19, 21]. The bridging azide groups are nearly linear and
show bent coordination with Cu atoms [N3–N4–N5 =
˚
the four donor atoms by 0.974(2) A. Each of the symmetry-
177.7(3)°, Cu1–N3–N4 = 123.9(2)°, Cu1–N5iv–N4iv
116.0(2)°].
=
related two central Cu atoms is in a severely distorted
square-pyramidal coordination, with the four azide N atoms
123

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Struct Chem (2012) 23:1489–1496
Fig. 4 The crystal structure of 2, viewed along the b axis
Fig. 2 The crystal structure of 1, viewed along the c axis. Hydrogen
bonds are shown as dashed lines
Fig. 5 A perspective view of the molecular structure of 3 with the
atom labeling scheme. The thermal ellipsoids are drawn at the 30%
probability level. Atoms labeled with the suffix A or unlabeled are at
the symmetry position -x, 1 - y, 1 - z
azide groups are nearly linear and show bent coordination
with Cu atoms.
Fig. 3 A perspective view of the molecular structure of 2 with the
atom labeling scheme. The thermal ellipsoids are drawn at the 30%
probability level. Atoms labeled with the suffix A or unlabeled are at
the symmetry position -1/2 ? x, -1/2 - y, -z
In the crystal structure, molecules are stacked along the
i
˚
a axis through pÁÁÁp interactions [Cg1ÁÁÁCg2 = 3.641(2) A,
i
˚
Cg2ÁÁÁCg2 = 3.817(2) A; Cg1 and Cg2 are the centroids
of Cu2–O1–C2–C1–C7–N1 and C1–C2–C3–C4–C5–C6
rings, respectively], as shown in Fig. 6.
defining the basal plane, and with the phenolate O atom
occupying the apical position. The deviation of the Cu1
atom from the least-squares plane defined by the basal
˚
donor atoms is 0.172(2) A. Significant distortion of the
IR spectra
square pyramid is revealed by bond lengths and angles
between the apical and basal donor atoms. The apical Cu–O
bond length is much longer than usual; the other bond
lengths are within normal ranges and comparable to the
corresponding values observed in 1, 2, and other Schiff base
Copper(II) complexes [22, 23]. The bridging and terminal
The IR spectra of the Schiff bases and the complexes
provide information about the metal–ligand bonding. The
assignments are based on the typical group frequencies.
The weak and sharp absorption at 3,248 cm-1 for 1 is
assigned to the vibration of the amino N–H groups. In the
123

Struct Chem (2012) 23:1489–1496
1495
Table 3 Average IC50 values of the tested materials against XO
Compound
IC50 (lM)
1
27.3 1.2
31.2 0.7
23.5 1.5
[100
2
3
HL1
HL2
HL3
[100
[100
25.33
Copper complex A [Ref. 10]
Copper complex B [Ref. 10]
Zinc complex [Ref. 21]
Allopurinol
21.27
7.23
10.2 0.4
Fig. 6 The crystal structure of 3, viewed along the a axis
characterized by elemental analysis, IR spectra, and sin-
gle-crystal X-ray crystallography. The azide ligands are
dramatic bridging groups for the construction of such
complexes. The complexes show moderate xanthine oxi-
dase inhibitory activities.
IR spectra of the complexes, the strong absorption bands at
1606 cm-1 (1), 1609 cm-1 (2), and 1610 cm-1 (3) are
assigned to the azomethine stretching frequencies of the
Schiff base ligands, whereas for the free Schiff bases the
corresponding bands are observed at higher wave numbers
of 1627–1638 cm-1. The shift of these bands toward lower
frequencies on complexation suggests coordination to the
Cu atoms through the imine N atoms. The m(C–O) mode is
present as middle bands at 1222 cm-1 for 1, 1233 cm-1 for
2, and 1223 cm-1 for 3. The intense bands at 2043 cm-1
for 1, and 2049 cm-1 for 2, as well as 2085, 2068, and
2044 cm-1 for 3, are assigned to the stretching vibration of
the azide ligands. There is only one intense absorption for
the azide groups in the spectrum of 1 or 2, while there are
three distinct intense absorptions for the azide groups in the
spectrum of 3. This is in accordance with the different
types of azide groups in the complexes. The weak bands
indicative of the Cu–O and Cu–N bonds are located in the
Supplementary material
CCDC-847218 (1), 847219 (2), and 847220 (3) contain the
supplementary crystallographic data for this article. These
data can be obtained free of charge at http://www.ccdc.
cam.ac.uk/const/retrieving.html or from the Cambridge
Crystallographic Data Centre (CCDC), 12 Union Road,
Cambridge CB2 1EZ, UK; fax: ?44(0)1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgment This study was financially supported by the
Natural Science Foundation of China (Project no. 20901036), and by
the Distinguished Young Scholars Program of Higher Education of
Liaoning Province (Grant no. LJQ2011114).
region 640–450 cm-1
.
XO inhibitory activity
References
The IC50 values for the compounds are listed in Table 3.
The complexes show stronger XO inhibitory activity than
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complexes we reported previously [13]. However, when
compared with the Zinc(II) complex we reported previously
[24], it can be seen that the activity of the Copper(II)
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