Influence of the steric effects of the Schiff bases and the hydrogen bonds on the bridging modes of the azide groups: Syntheses and crystal structures of three azide-bridged Schiff base zinc(II) complexes

Article abstract of DOI:10.1016/j.inoche.2009.03.009

Three polymeric zinc(II) complexes, derived from the end-on azide (μ_1,1-N₃) and end-to-end azide (μ_1,3-N₃) bridges and similar tridentate Schiff base ligands, have been synthesized and structurally characterized

Full text of DOI:10.1016/j.inoche.2009.03.009

Inorganic Chemistry Communications 12 (2009) 444–446
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Influence of the steric effects of the Schiff bases and the hydrogen bonds
on the bridging modes of the azide groups: Syntheses and crystal structures
of three azide-bridged Schiff base zinc(II) complexes
*
Zhong-Lu You , Peng Hou, Li-Li Ni, Song Chen
Department of Chemistry and Chemical Engineering, Liaoning Normal University, Huanghe Road 850#, Dalian, Liaoning 116029, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three polymeric zinc(II) complexes, derived from the end-on azide (l1,1-N3) and end-to-end azide
(l1,3-N3) bridges and similar tridentate Schiff base ligands, have been synthesized and structurally
characterized. The zinc(II) atom in each complex is in a midway between trigonal–bipyramidal and
square–pyramidal coordination. The slight difference of the steric effects of the Schiff bases and the
hydrogen bonds can influence the bridging modes of the azide groups.
Received 5 February 2009
Accepted 19 March 2009
Available online 26 March 2009
Keywords:
Synthesis
Schiff base
Zinc
Crown Copyright Ó 2009 Published by Elsevier B.V. All rights reserved.
Azide
Crystal structure
Polynuclear complexes with bridging groups are currently
attracting attention for their interesting molecular topologies and
crystal packing motifs, as well as the fact that they may be de-
signed with specific functionalities [1]. As is well known, the azide
through the phenolic oxygen, imine nitrogen and amine nitrogen
atoms [4]. The mere difference lies in the steric effects of the termi-
nal groups. It is notable that the Schiff bases HL2 and HL3 were
newly synthesized and the metal complexes of them have never
been reported previously. For HL1, only one mononuclear cop-
per(II) complex has been reported [5]. The complexes showed
weak inhibitory activity against urease.
The three Schiff bases were prepared by reaction of the corre-
sponding aldehydes with the amines in methanol solutions and
subsequent evaporation of the solvent [6]. All the complexes were
synthesized according to the same method: A methanol solution
(2 ml) of Zn(NO3)2 Á 6H2O (0.1 mmol, 27.1 mg) was added with stir-
ring to a methanol solution (10 ml) of NaN3 (0.1 mmol, 6.5 mg) and
the corresponding Schiff base (0.1 mmol). The mixture was stirred
at room temperature for 30 min to give a colorless solution. X-ray
quality colorless block-shaped single crystals were formed by slow
evaporation of the solution in air for a few days. Yield: 73% (1), 81%
(2), and 65% (3) [7].
ligand can adopt end-on (l1,1-N3), end-to-end (l1,3-N3), and many
other coordination modes when it links different metal atoms,
forming versatile polynuclear structures [2]. However, given the
present state of knowledge, it is not possible to determine which
coordination mode will be adopted by the azide group and what
structures will finally be formed. Although Schiff base complexes
with azide bridges have been extensively studied, Schiff base
zinc(II) complexes involving azide bridges have seldom been re-
ported [3]. Study the influence of the Schiff base ligands and the
hydrogen bonds on the coordination modes of the azide groups
may help us better understand and control the topologies of
the azide-bridged complexes. In this paper, three new azide-
bridged polymeric zinc(II) complexes with similar Schiff bases,
[ZnL1(l1,1-N3)ZnL1(l1,3-N3)]n (1), [ZnL2(l1,1-N3)ZnL2(l1,1-N3)]n
(2), and [ZnL3(
l
1,3-N3)ZnL3(
l
1,3-N3)]n (3) (L1 = 1-[(2-propylamino-
X-ray crystallography [8] reveals that the structures of the com-
plexes are similar one-dimensional chains, except for the different
coordination modes of the azide bridges. Complex 1 (Fig. 1) is an
alternate end-on and end-to-end azide-bridged polymeric zinc(II)
compound. Complex 2 (Fig. 2) is a pure end-on azide-bridged poly-
meric zinc(II) compound. And complex 3 (Fig. 3) is a pure end-to-
end azide-bridged polymeric zinc(II) compound.
ethylimino)methyl]naphthalen-2-olate, L2 = 2-bromo-4-chloro-6-
[(2-propylaminoethylimino)methyl]phenolate, and L3 = 2-bromo-
4-chloro-6-[(2-piperidin-1-ylethylimino)methyl]phenolate;
Scheme 1), have been synthesized to investigate the influence of
the Schiff bases and the hydrogen bonds on the bridging modes
of the azide. The three Schiff bases in this paper are very similar
tridentate ligands, which can coordinate to the metal atoms
see
In each complex, the coordination of the Zn atom may be
regarded as midway between trigonal–bipyramidal and square–
pyramidal as described by the
s parameters, an index of the degree
* Corresponding author.
of trigonality [9]. The values calculated for the complexes are
s
E-mail address: youzhonglu@yahoo.com.cn (Z.-L. You).
1387-7003/$ - see front matter Crown Copyright Ó 2009 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2009.03.009

Z.-L. You et al. / Inorganic Chemistry Communications 12 (2009) 444–446
445
H
N
Cl
H
N
Cl
N
N
N
N
OH
OH
OH
HL1
Br
Br
HL2
Scheme 1. Schematic views of the Schiff bases.
HL3
Fig. 3. Molecular structure of 3 and the atomic numbering scheme. Intramolecular
hydrogen bonds are shown as dashed lines. Selected bond lengths (Å) and bond
angles (°): Zn1–O1 2.008(3), Zn1–N1 2.032(4), Zn1–N2 2.219(3), Zn1–N3 2.013(4),
Zn1–N5 2.073(4), O1–Zn1–N3 91.8(2), O1–Zn1–N1 87.3(2), N3–Zn1–N1 140.2(2),
O1–Zn1–N5 97.2(2), N3–Zn1–N5 106.6(2), N1–Zn1–N5 113.0(2), O1–Zn1–N2
166.2(2), N3–Zn1–N2 91.1(2), N1–Zn1–N2 81.9(2), N5–Zn1–N2 94.9(2).
In 1 and 2, the basal plane of the trigonal–bipyramid is fur-
nished by one imine nitrogen atom of the Schiff base ligand and
two nitrogen atoms from two azide groups, and the axial positions
are occupied by one phenolic oxygen and one amine nitrogen
atoms of the Schiff base ligand. The Zn atoms deviate by
0.016(2) Å in 1 and 0.014(2) Å in 2, respectively, from the least-
squares plane defined by the three basal donor atoms. In 3, the ba-
sal plane of the square pyramid is furnished by one phenolic oxy-
gen, one imine nitrogen and one amine nitrogen atoms of the Schiff
base ligand and one nitrogen atom of an azide group, and the apical
position is occupied by one nitrogen atom of another azide group.
The Zn atom deviates by 0.051(2) Å in 3 from the least-squares
plane defined by the four basal donor atoms. Close examination
of the structures revealed that the Zn–O and Zn–N bond lengths
are comparable to each other, and can be considered as normal
by comparison with those reported in the literatures [3,4a].
In 1, there exists two intermolecular N–HÁ Á ÁO hydrogen bonds
(Table 1) between the adjacent two complex moieties, which made
the two Zn atoms close to each other, and the azide group adopts
end-on bridging mode, with the ZnÁ Á ÁZn distance of 3.362(2) Å.
While the adjacent two complex moieties without hydrogen bonds
are deviate from each other, with the azide group has no choice but
adopts end-to-end bridging mode, the ZnÁ Á ÁZn distance between
them is 5.371(2) Å. In 2, there exists equivalent intermolecular
N–HÁ Á ÁO hydrogen bonds between each adjacent moieties, which
made the two Zn atoms close to each other, and the azide groups
adopt end-on bridging mode, with the ZnÁ Á ÁZn distances of
3.681(2) Å. And in 3, there are no intermolecular hydrogen bonds
Fig. 1. Molecular structure of 1 and the atomic numbering scheme. Intermolecular
hydrogen bonds are shown as dashed lines. Selected bond lengths (Å) and bond
angles (°): Zn1–O1 2.033(2), Zn1–N1 2.028(3), Zn1–N2 2.185(3), Zn1–N3 2.043(2),
Zn1–N6 2.020(3), N6–Zn1–N1 117.3(2), N6–Zn1–O1 96.8(2), N1–Zn1–O1 85.6(1),
N6–Zn1–N3 113.0(2), N1–Zn1–N3 129.6(2), O1–Zn1–N3 90.0(1), N6–Zn1–N2
97.0(2), N1–Zn1–N2 81.9(1), O1–Zn1–N2 164.5(2), N3–Zn1–N2 91.1(1).
Table 1
Hydrogen bond distances (Å) and bond angles (°) for the complexes.
D–HÁ Á ÁA
d(D–H)
d(HÁ Á ÁA)
d(DÁ Á ÁA)
Angle (D–HÁ Á ÁA)
Fig. 2. Molecular structure of 2 and the atomic numbering scheme. Intermolecular
hydrogen bonds are shown as dashed lines. Selected bond lengths (Å) and bond
angles (°): Zn1–O1 2.037(2), Zn1–N1 2.049(2), Zn1–N2 2.181(2), Zn1–N3 2.092(2),
Zn1–N3i 2.118(2), O1–Zn1–N1 87.4(1), O1–Zn1–N3 89.2(1), N1–Zn1–N3 120.1(1),
O1–Zn1–N3i 94.5(1), N1–Zn1–N3i 117.2(1), N3–Zn1–N3i 122.7(2), O1–Zn1–N2
167.8(1), N1–Zn1–N2 80.5(1), N3–Zn1–N2 95.8(1), N3i–Zn1–N2 92.1(1). Symmetry
code for i: x, 1/2 À y, À1/2 + z.
1
N2–H2Á Á ÁO1#1
0.899(10)
2.23(2)
3.079(4)
158(4)
2
N2–H2Á Á ÁO1#2
N2–H2Á Á ÁBr1#2
C6–H6Á Á ÁN5#3
0.896(10)
0.896(10)
0.93
2.191(18)
3.08(3)
2.57
3.042(3)
3.714(2)
3.359(3)
159(4)
130(3)
144(3)
3
C10–H10BÁ Á ÁN3
0.97
0.97
2.47
2.62
3.053(3)
3.092(3)
118(3)
110(3)
0.582 for 1, 0.752 for 2, and 0.433 for 3, respectively. It can be seen
that the coordination of the Zn atoms in 1 and 2 is close to dis-
torted trigonal-bipyramidal, while that in 3 is close to distorted
square pyramidal.
C14–H14BÁ Á ÁN5
Symmetry transformations used to generate the equivalent atoms: #1: 1/2 À x, À1/
2 À y, z; #2: x, 1/2 À y, À1/2 + z; #3: 1 + x, 1/2 À y, À1/2 + z.

446
Z.-L. You et al. / Inorganic Chemistry Communications 12 (2009) 444–446
Table 2
obtained free of charge from The Cambridge Crystallographic Data
Inhibition of urease by the tested materials.
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.inoche.2009.03.009.
a
Tested materials
IC50
(lM)
1
>100
2
3
HL1
72.19 0.70
77.36 0.53
>100
References
HL2
HL3
>100
>100
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Zinc acetate
Acetohydroxamic acid
31.45 0.39
45.32 0.27
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a
All IC50 values were expressed as mean S.D. values of the three parallel tests.
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between the adjacent moieties as those in 1 and 2, instead, there
exists intramolecular C–HÁ Á ÁN hydrogen bonds. The lack of inter-
molecular hydrogen bonds, as well as the large steric effects of
the cyclohexyl groups in 3 lead to the two adjacent moieties devi-
ate from each other, and the azide groups adopt end-to-end bridg-
ing mode. The ZnÁ Á ÁZn distances are 5.879(2) and 5.545(2) Å,
respectively.
It can be seen that the hydrogen bonds in 1 and 2 influence the
bridging modes of the azide groups, while that in 3, the steric ef-
fects of the terminal cyclohexyl group appears more convincing.
The measurement of jack bean urease inhibitory activity was
carried out for three parallel times according to the literature phe-
nol-red method [10]. The acetohydroxamic acid was used as a po-
sitive reference. The results are summarized in Table 2. Complex 1
shows no activity, while 2 and 3 show weak activity against the en-
zyme. The results in this paper are accordance with those reported
previously, that the zinc(II) complexes have much weak urease
inhibitory activities [11].
(d) W.J. Evans, S.A. Kozimor, J.W. Ziller, Science 309 (2005) 1835.
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(b) Z.-L. You, D.-H. Shi, H.-L. Zhu, Inorg. Chem. Commun. 9 (2006) 642;
(c) H.-D. Bian, W. Gu, J.-Y. Xu, F. Bian, S.-P. Yan, D.-Z. Liao, Z.-H. Jiang, P. Cheng,
Inorg. Chem. 42 (2003) 4265.
[5] C.-G. Zhu, Y.-J. Wei, F.-W. Wang, Acta Crystallogr. E63 (2007) m3197.
[6] Anal. Calc. for C16H22N2O (HL1): C 74.4, H 8.6, N 10.8%. Found: C 74.7, H 8.5, N
11.0%. Anal. Calc. for C12H16BrClN2O (HL2): C 45.1, H 5.0, N 8.8%. Found: C 45.5,
H 5.2, N 8.7%. Anal. Calc. for C14H18BrClN2O (HL3): C 48.6, H 5.2, N 8.1%. Found:
C 48.1, H 5.2, N 8.3%. Selected IR data (KBr, cmÀ1): HL1,
m
1632 (s, C@N); HL2,
m
1645 (s, C@N); HL3,
m
1643 (s, C@N). 1HNMR data (CDCl3, ppm): HL1, d = 0.91
(t, 3H), 1.53 (m, 2H), 2.17 (s, 1H), 2.56 (t, 2H), 2.96 (t, 2H), 3.56 (t, 2H), 7.12 (d,
1H), 7.14 (t, 1H), 7.21 (t, 1H), 7.45 (d, 1H), 7.60 (d, 1H), 7.78 (d, 1H), 8.17 (s,
1H); HL2, d = 0.91 (t, 3H), 1.53 (m, 2H), 2.16 (s, 1H), 2.56 (t, 2H), 2.96 (t, 2H),
3.57 (t, 2H), 7.14 (s, 1H), 7.51 (s, 1H), 8.19 (s, 1H); HL3, d = 1.43 (m, 2H), 1.56
(m, 4H), 2.16 (s, 1H), 2.44 (t, 4H), 2.63 (t, 2H), 3.72 (t, 2H), 7.13 (d, 1H), 7.54 (d,
1H), 8.18 (s, 1H).
In summary, the present study reports the synthesis, structures
and urease inhibitory activity of three azide-bridged polymeric
Schiff base zinc(II) complexes. The steric effects of the Schiff bases
and the hydrogen bonds can influence the bridging modes of the
azide groups. The urease inhibitory activities of the zinc(II) com-
plexes are not very satisfactory.
[7] Anal. Calc. for C16H19N5OZn (1): C 53.0, H 5.3, N 19.3%. Found: C 53.6, H 5.4, N
19.0%. Anal. Calc. for C12H15BrClN5OZn (2): C 33.8, H 3.5, N 16.4%. Found: C
33.4, H 3.6, N 16.6%. Anal. Calc. for C14H17BrClN5OZn (3): C 37.2, H 3.8, N 15.5%.
Found: C 37.5, H 4.0, N 15.2%. Selected IR data (KBr, cmÀ1): 1,
m
2106 (vs, N3),
m
2066 (sh, vs, N3),
m
1619 (s, C@N). 2,
m
2100 (vs, N3),
m
1633 (s, C@N). 3,
m
2145
(s, N3), 2087 (vs, N3),
m
m
1632 (s, C@N).
[8] Crystal data for 1 (C16H19N5OZn): Mt = 362.73, orthorhombic, space group
Pccn, a = 22.232(2), b = 8.639(2), c = 17.222(3) Å, V = 3307.7(10) Å3, Z = 8,
q
calcd = 1.457 g cmÀ3 (MoK ) = 1.496 mmÀ1
, l , R1 = 0.0418, wR2 = 0.1057 (all
a
data), T = 298 K. Crystal data for 2 (C12H15BrClN5OZn): Mt = 426.02, monoclinic,
space group P21/c, a = 9.423(2), b = 22.685(3), c = 7.318(2) Å, b = 94.94(3)°
Acknowledgement
V = 1558.5(6) Å3,
Z = 4,
q
calcd = 1.816 g cmÀ3
,
l
(MoK ) = 4.316 mmÀ1
,
a
This work was financially supported by the Office of Dalian Sci-
ence & Technology (Project No. 2007J23JH018) and by the Educa-
tion Office of Liaoning Province (Project No. 2007T092).
R1 = 0.0368, wR2 = 0.0884 (all data), T = 298 K. Crystal data for
3
(C14H17BrClN5OZn): Mt = 452.06, monoclinic, space group C2/c, a = 28.679(3),
b = 7.039(1), c = 18.881(2) Å, b = 117.33(3)°, V = 3386.1(12) Å3, Z = 8, qcalcd
=
1.774 g cmÀ3 (MoK ) = 3.979 mmÀ1
, l , R1 = 0.0452, wR2 = 0.1038 (all data),
a
T = 298 K.
[9] A.W. Addison, T.N. Rao, J. Reedijk, J. van Riju, G.C. Verschoor, J. Chem. Soc.
Dalton Trans. (1984) 1349.
Appendix A. Supplementary material
[10] (a) T. Tanaka, M. Kawase, S. Tani, Life Sci. 73 (2003) 2985;
(b) Z.-L. You, P. Zhou, Inorg. Chem. Commun. 10 (2007) 1273.
[11] K. Cheng, Z.-L. You, H.-L. Zhu, Aust. J. Chem. 60 (2007) 375.
CCDC 719165 (1), 719166 (2), and 719167 (3) contain the sup-
plementary crystallographic data for this paper. These data can be