Synthesis and crystal structures of a pair of isostructural azido-bridged polynuclear Schiff base zinc(II) complexes

Article abstract of DOI:10.1007/s10870-011-0145-0

A pair of novel isostructural azido-bridged polynuclear zinc(II) complexes, [Zn₂(L1)₂(μ_1,1-N₃)(μ _1,3-N₃)] _n (1) and [Zn₂(L2) ₂(μ_1,1-N₃

Full text of DOI:10.1007/s10870-011-0145-0

J Chem Crystallogr (2011) 41:1593–1597
DOI 10.1007/s10870-011-0145-0
ORIGINAL PAPER
Synthesis and Crystal Structures of a Pair of Isostructural
Azido-Bridged Polynuclear Schiff Base Zinc(II) Complexes
•
Heng-Yu Qian Zhong-Lu You
Received: 13 January 2009 / Accepted: 31 May 2011 / Published online: 11 June 2011
Ó Springer Science+Business Media, LLC 2011
Abstract A pair of novel isostructural azido-bridged poly-
nuclear zinc(II) complexes, [Zn2(L1)2(l1,1-N3)(l1,3-N3)]n
(1) and [Zn2(L2)2(l1,1-N3)(l1,3-N3)]n (2) (HL1 = 2-bromo-
4-chloro-6-[(2-isopropylaminoethylimino)methyl]phenol,
HL2 = 2,4-dibromo-6-[(2-isopropylaminoethylimino)-
methyl]phenol), have been synthesized and structurally
characterized by elemental analysis, IR spectra and single
crystal X-ray diffraction. Both complexes crystallize in the
orthorhombic space group Pcca. Crystal data for (1): a =
Keywords Zinc Á Polynuclear Á Schiff base Á Synthesis Á
Crystallography
Introduction
Polynuclear complexes have been widely investigated due
to their versatile molecular structures and interesting
functionalities [1–3]. The prime strategy for designing the
polynuclear complexes is to use suitable bridging ligands,
such as azide, thiocyanate, cyanide, and so on [4–7].
Among the bridging groups, azide is the preference.
Depending upon the steric and electronic demand of the
co-ligands, the azido group has been shown to be able to
link two or more metal ions in various bridging modes such
as l1,3, l1,1, l1,1,1, l1,1,3, etc. to give birth to a variety of
one-, two-, and three-dimensional species using Schiff
bases or other polydentate organics as auxillary ligands [8–11].
The versatile features of metal-azido systems in coordination
chemistry may lead to novel topologies that are difficult to
achieve with other bridging ligands, but a major obstacle is
impossible to predict which coordination modes will be
adopted by the azide ligand. For the zinc(II) complexes, the
azide bridges usually adopt l1,1 mode [12–16]. It is sur-
prising that the l1,3 mode is not observed for the azido-
bridged zinc(II) complexes through the CSD search, except
for one sample containing both l1,1 and l1,3 azido bridges
[17]. In this article, a pair of novel azido-bridged polynuclear
zinc(II) complexes, [Zn2(L1)2(l1,1-N3)(l1,3-N3)]n (1) and
[Zn2(L2)2(l1,1-N3)(l1,3-N3)]n (2) (Scheme 1; HL1 =
2-bromo-4-chloro-6-[(2-isopropylaminoethylimino)methyl]-
phenol, HL2 = 2,4-dibromo-6-[(2-isopropylaminoethylimino)-
methyl]phenol), have been synthesized and structurally
characterized by elemental analysis, IR spectra and single-crystal
˚
22.567(4) A, b = 8.414(2) A, c = 17.268(3) A, V = 3279.0
˚
˚
3
(11) A , Z = 8, R1 = 0.0441, and wR2 = 0.0846. Crystal
˚
˚
data for (2): a = 22.536(4) A, b = 8.409(2) A, c =
˚
3
˚
˚
17.531(3) A, V = 3322.2(11) A , Z = 8, R1 = 0.0538, and
wR2 = 0.0906. X-ray structure determination revealed
that each zinc(II) atom in the complexes is in a trigonal–
bipyramidal coordination, with one imine N atom of a Schiff
base ligand and two N atoms from two bridging azide ligands
defining the basal plane, and one phenolate O and one amine
N atoms of the Schiff base ligand occupying the two axial
positions.
H.-Y. Qian (&)
Key Laboratory of Surface and Interface Science of Henan,
School of Material & Chemical Engineering, Zhengzhou
University of Light Industry, Zhengzhou 450002,
People’s Republic of China
e-mail: hengyu_qian@126.com
Z.-L. You
Department of Chemistry and Chemical Engineering, Liaoning
Normal University, Dalian 116029, People’s Republic of China
123

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J Chem Crystallogr (2011) 41:1593–1597
X
temperature and filtered. Upon keeping the filtrate in air for a
week, colorless block-shaped crystals of (1), suitable for
X-ray crystal structure determination, 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
a vacuum desiccator containing anhydrous CaCl2. Yield
62% on the basis of HL1. (Found: C, 33.2; H, 3.7; N, 16.0.
Calc. for C12H15BrClN5OZn: C, 33.8; H, 3.5; N, 16.4%).
X
Br
Br
N
O
O
N
N
Zn
N
N
N
Zn
Synthesis of the Complex [Zn2(L2)2(l1,1-N3)(l1,3-N3)]n
N
Complex (2) was prepared by the similar procedure as
described for (1), with HL1 replaced by HL2 (36.4 mg,
0.1 mmol), resulting colorless block-shaped crystals of (2).
Yield 71% on the basis of HL2. (Found: C, 30.9; H, 3.5; N,
14.5. Calc. for C12H15Br2N5OZn: C, 30.6; H, 3.2; N, 14.9%).
Et
N
Et
N
N
Scheme 1 X = Cl for (1), X = Br for (2)
Table 1 Crystal data and refinement parameters for the complexes
X-ray diffraction. The results indicates that the hydrogen bonds
can influence the bridging modes of the azide ligands.
Complex
1
2
Molecular formula
Molecular weight
Temperature (K)
Crystal shape
C12H15BrClN5OZn
426.0
C12H15Br2N5OZn
470.5
Experimental
298(2)
298(2)
block
block
Materials and Measurements
Crystal dimensions
(mm); colour
0.27 9 0.23 9 0.20; 0.28 9 0.27 9 0.27;
colorless
Orthorhombic
Pcca
colorless
Orthorhombic
Pcca
3-Bromo-5-chlorosalicylaldehyde, 3,5-dibromosalicylalde-
hyde and N-isopropylethane-1,2-diamine were purchased
from Lancaster. All other chemicals (reagent grade) were
commercially available and were used without further
purification. Elemental analyses for C, H and N were
performed on a Perkin-Elmer 240C elemental analyzer. IR
spectra were recorded on a Nicolet AVATAR 360 spec-
trophotometer as KBr pellets in the 4000–400 cm-1 region.
Crystal system
Space group
˚
a (A)
22.567(4)
8.414(2)
17.268(3)
3279.0(11)
8
22.536(4)
8.409(2)
17.531(3)
3322.2(11)
8
˚
b (A)
˚
c (A)
3
˚
Volume (A )
Z
Dcalc (g cm-3
)
1.726
1.881
Absorption coefficient 4.103
(mm-1
F(000)
h range (o)
6.294
Synthesis of the Schiff Bases HL1 and HL2
)
1696
1840
HL1 and HL2 were synthesized by the condensation of
equimolar quantities of N-isopropylethane-1,2-diamine
with 3-bromo-5-chlorosalicylaldehyde and 3,5-dibromo-
salicylaldehyde, respectively, in methanol solutions at
room temperature. Yield: 92% for HL1 and 97% for HL2.
(Found: C, 45.5; H, 5.4; N, 8.6. Calc. for HL1: C, 45.1; H,
5.1; N, 8.8%. Found: C, 39.3; H, 4.5; N, 7.9. Calc. for HL2:
C, 39.6; H, 4.4; N, 7.7%).
1.80/27.49
1.81/27.50
Range/indices (h, k, l) -28/28, -10/10,
-22/22
-29/29, -10/10,
-22/22
Absorption correction Empirical
Empirical
0.272
Tmin
Tmax
0.404
0.494
0.281
Reflections/Parameters 3760/197
3811/197
1707
Independent
reflections
2069
Restraints
Goodness of fit on F2 1.000
1
1
Synthesis of the Complex [Zn2(L1)2(l1,1-N3)(l1,3-N3)]n
0.981
R1, wR2 [I C 2r(I)]a
R1, wR2 (all data)a
0.0441, 0.0846
0.0538, 0.0906
To an anhydrous methanol solution (5 mL) of
Zn(CH3COO)2Á2H2O (22.0 mg, 0.1 mmol) was added a
methanol solution (10 mL) of HL1 (31.9 mg, 0.1 mmol) and
a methanol solution (5 mL) of NaN3 (6.5 mg, 0.1 mmol)
with stirring. The mixture was stirred for 30 min at room
0.1048, 0.1069
P
0.1568, 0.1205
P
P
P
a
|
R1 = ||Fo| - F|c|/ |F|o, wR2 = [ w(F2o - Fc2)2/ w(F2o)2]1/2, w1 =
[r2F2o ? (0.0226(Fo2 ? 2Fc2)/3)2 ? 3.8229(Fo2 ? 2F2c)/3]-1, w2 = [r2F2o ?
(0.0336(F2o ? 2Fc2)/3)2 ? 2.6831(Fo2 ? 2F2c)/3]-1
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J Chem Crystallogr (2011) 41:1593–1597
X-ray Crystallography
1595
X-ray diffraction intensities of the complexes were collected
using a Bruker Smart APEXII CCD area detector equipped
with graphite-monochromated MoK radiation (k =
˚
0.71073 A) at 298(2) K. Empirical absorption corrections
were applied using the SADABS program [18]. The struc-
tures were solved by the direct method and refined by full-
matrix least squares on F2 using the SHELXTL package
[19]. All non-hydrogen atoms were refined anisotropically.
Atoms H2 in both (1) and (2) attached to N2 were located in
difference Fourier maps and refined isotropically, with N–H
˚
distances restrained to 0.90(1) A. All other H atoms were
placed in calculated positions and constrained to ride on their
˚
parent atoms, with C–H distances in the range 0.93–0.97 A,
and with Uiso (H) set at 1.2Ueq (C) and 1.5Ueq (methyl C).
The crystallographic data for the two complexes are sum-
marized in Table 1.
Fig. 1 Molecular structure of (1) at 30% probability displacement.
H atoms not involved in the hydrogen bonding have been omitted for
clarity. Atoms labeled with the suffix A are at the symmetry position
3/2 - x, 1 - y, z. Hydrogen bonds are shown as dashed lines
The elemental analyses are in good agreement with the
chemical formulae proposed for the compounds.
Results and Discussion
Selected bond lengths and angles are given in Table 2.
The two complexes were synthesized under the same
synthetic procedures with similar starting materials.
Crystal Structure Description of the Complexes
Figures 1 and 2 give perspective views of the complexes
(1) and (2) together with the atomic labeling system. Both
complexes are one-dimensional zinc(II)-azido chains
with alternately end-on and end-to-end azido bridges.
The asymmetric unit of each complex consists of one
[ZnL(l1,1-N3)ZnL(l1,3-N3)] (L = L1 for (1) and L2
for (2)) moiety. Each ZnII ion in the complexes is in a
Table 2 Selected bond distances (A) and angles (o) for the
complexes
˚
(1)
Bond distances
Zn1–O1
2.054(3)
2.212(4)
2.037(4)
Zn1–N1
Zn1–N3
2.040(4)
2.044(3)
Zn1–N2
Zn1–N6
Bond angles
N6–Zn1–N1
N1–Zn1–N3
N1–Zn1–O1
N6–Zn1–N2
N3–Zn1–N2
(2)
119.8(2)
127.9(2)
85.9(2)
99.3(2)
94.4(2)
N6–Zn1–N3
N6–Zn1–O1
N3–Zn1–O1
N1–Zn1–N2
O1–Zn1–N2
112.2(2)
94.4(2)
87.4(2)
80.8(2)
164.4(2)
Bond distances
Zn1–O1
2.059(4)
2.208(5)
2.032(5)
Zn1–N1
Zn1–N3
2.049(5)
2.034(4)
Zn1–N2
Zn1–N6
Bond angles
N6–Zn1–N1
N1–Zn1–N3
N1–Zn1–O1
N6–Zn1–N2
N3–Zn1–N2
119.5(2)
127.5(2)
86.1(2)
98.8(2)
94.6(2)
N6–Zn1–N3
N6–Zn1–O1
N3–Zn1–O1
N1–Zn1–N2
O1–Zn1–N2
112.9(2)
94.4(2)
87.5(2)
80.6(2)
164.7(2)
Fig. 2 Molecular structure of (2) at 30% probability displacement. H
atoms not involved in the hydrogen bonding have been omitted for
clarity. Atoms labeled with the suffix A are at the symmetry position
1/2 - x, -y, z. Hydrogen bonds are shown as dashed lines
123

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J Chem Crystallogr (2011) 41:1593–1597
trigonal–bipyramidal coordination, with one imine N atom
of the Schiff base ligand and two N atoms from two
bridging azido ligands defining the basal plane, and with
one phenolate O and one amine N atoms of the Schiff base
ligand occupying the axial positions. In both structures, the
coordinate bond lengths are typical and comparable with
each other, and similar to the corresponding values
observed in other Schiff base zinc(II) complexes [20–22].
In (1), the bond angle N1–Zn1–N2 deviates from 90o by
9.2(2)o, and in (2), the bond angle N1–Zn1–N2 deviates
from 90o by 9.4(2)o, which are caused by the strain created
by the corresponding five-membered chelate rings.
The bond angles O1–Zn1–N2 in (1) and (2) deviate from
180o by 15.6(2) and 15.3(2)o, respectively, indicating the
distortion of each trigonal–bipyramidal coordination. Each
of the azido ligands is nearly linear and shows bent
coordination modes with the metal atoms [In (1), N3–N4–
N5/Zn1–N3–N4/Zn1A–N3–N4/N6–N7–N6A/Zn1–N6–N7 =
180.0(1)o/124.4(2)o/124.4(2)o/176.5(7)o/126.5(3)o; In (2),
N3–N4–N5/Zn1–N3–N4/Zn1A–N3–N4/N6–N7–N6A/Zn1–
N6–N7 = 180.0(1)o/124.2(2)o/124.2(2)o/178.6(10)o/126.9(5)o].
In (1) and (2), the ZnÁÁÁZn distances are 3.375(1) and
˚
3.365(1) A, respectively. It should be addressed that there
are two N–HÁÁÁO hydrogen bonds between the l1,1-N3
bridged [CuL] units, which is not observed between the
l1,3-N3 bridged units, indicating the essential influence of
the hydrogen bonding on the bridging modes of the azide
groups.
In looking at the unit cell parameters, the only really
noteworthy variation between these two structures occurs
along the c-axis. The c-axis for the unit cell in (1) with
˚
17.268(3) A is shorter than that in (2) with 17.531(3) A,
˚
Fig. 3 Molecular packing
arrangement of (1) (X = Cl)
and (2) (X = Br). Viewed along
the a axis
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J Chem Crystallogr (2011) 41:1593–1597
1597
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˚
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bond values between the two structures. The molecular
packing diagram for the two complexes is shown in Fig. 3,
in which the molecules are linked through bridging azido
ligands, forming chains running along the b axis.
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structurally characterized. The Schiff bases HL1 and HL2
coordinate to the Zn atoms through the phenolate O, imine
N and amine N atoms. The synthesis of the two complexes
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