Anion-controlled syntheses and crystal structures of a pair of novel azide-bridged copper(II) complexes constructed from 4-chloro-2-[(2- dimethylaminoethylimino)methyl]phenol

Article abstract of DOI:10.1002/zaac.200600198

A pair of novel azide-bridged polynuclear copper(II) complexes, [CuL(μ_1,1-N₃)]_n (1) and [Cu ₄L₂(CH₃COO)₂(μ _1,1-N₃)₄] (2) (L = 4-chloro-2-[(2- dimethylaminoethylimino)methyl]phenolate), have been obtained from the same Schiff base ligand and an identical synthetic procedure using anions of the metal salts as the only independent variable. Complex 1 was synthesized using copper(II) nitrate, while complex 2 was synthesized using the copper(II) acetate as the salt. Both of the complexes show novel supramolecular structures in their crystals as elucidated by X-ray analyses. The polynuclear complex 1 contains [CuL(μ_1,1-N₃)]_n units as the building blocks, crystallizes in the Pbca space group. The tetra-nuclear complex 2 contains [Cu₄L₂(CH₃COO)₂(μ _1,1-N₃)₄] units as the building blocks, crystallizes in the P1 space group.

Full text of DOI:10.1002/zaac.200600198

DOI: 10.1002/zaac.200600198
Anion-controlled Syntheses and Crystal Structures of a Pair of Novel
Azide-bridged Copper(II) Complexes Constructed from
4-Chloro-2-[(2-dimethylaminoethylimino)methyl]phenol
Zhong-Lu You*, Qing-Zhu Jiao, Shu-Yun Niu, and Jing-Yun Chi
Dalian / P. R. China, Department of Chemistry and Chemical Engineering, Liaoning Normal University
Received July 11th, 2006.
Abstract. A pair of novel azide-bridged polynuclear copper(II)
complexes, [CuL(µ1,1-N3)]n (1) and [Cu4L2(CH3COO)2(µ1,1-N3)4]
(2) (L ϭ 4-chloro-2-[(2-dimethylaminoethylimino)methyl]pheno-
late), have been obtained from the same Schiff base ligand and an
identical synthetic procedure using anions of the metal salts as the only
independent variable. Complex 1 was synthesized using copper(II)
nitrate, while complex 2 was synthesized using the copper(II) ace-
tate as the salt. Both of the complexes show novel supramolecular
structures in their crystals as elucidated by X-ray analyses. The
polynuclear complex 1 contains [CuL(µ1,1-N3)]n units as the buil-
ding blocks, crystallizes in the Pbca space group. The tetra-nuclear
complex 2 contains [Cu4L2(CH3COO)2(µ1,1-N3)4] units as the buil-
¯
ding blocks, crystallizes in the P1 space group.
Keywords: Copper(II) complexes; Polynuclear complexes; Schiff
bases; Crystal structure; Supramolecular assembly
Introduction
[(2-dimethylaminoethylimino)methyl]phenolate), from an
identical synthetic procedure and the same Schiff base
ligand but with different copper(II) salts.
Metal-organic complexes containing bridging ligands are of
great interest because of their interesting molecular top-
ologies as well as the fact that they may be designed with
specific functionalities [1Ϫ3]. Among pseudohalogens,
azide has become the most extensively studied building
blocks in the multi-dimensional complexes due to its versa-
tility and probability in functioning as a bridging ligand to
give varieties of coordination modes [4Ϫ6]. A major ob-
stacle to a more comprehensive study of such azide-based
polymeric coordination complexes is the lack of rational
synthetic procedures, since with the present state of knowl-
edge it is hardly possible to determine which coordination
mode will be adopted by the azide ligand and whether the
sought-after alternating chain structure will finally be
formed [7Ϫ9]. Furthermore, the design and syntheses of no-
vel coordination modes controlled by varying the reaction
conditions (including temperature [10Ϫ12], metal/ligand
ratio [13], pH values [14], solvents [15], and counter anions
[16, 17]) are of great interest in coordination chemistry. Ap-
propriate control of the reaction conditions makes it pos-
sible to construct new materials with useful properties. In
this paper, we report the syntheses of a pair of novel azide-
bridged polynuclear copper(II) complexes, [CuL(µ1,1-N3)]n
(1) and [Cu4L2(CH3COO)2(µ1,1-N3)4] (2) (L ϭ 4-chloro-2-
Experimental Section
Materials and measurements
All 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 spectrometer as
KBr pellets in the 4000-400 cmϪ1 region.
Preparation of the ligand HL
To a MeOH solution (20 mL) of 5-chlorosalicylaldehyde (157.7 mg,
1.0 mmol) was added a MeOH solution (10 mL) of N,N-dimethyl-
ethane-1,2-diamine (88.2 mg, 1.0 mmol) with stirring. The mixture
was stirred for 10 min at room temperature to give a clear orange
solution. The ligand was not isolated from the solution. The
MeOH solution was used for the syntheses of the complexes.
Preparation of the complexes
[CuL(µ1,1-N3)]n (1). To a MeOH solution (5 mL) of Cu(NO3)2·
3H2O (48.5 mg, 0.2 mmol) was added a MeOH solution (10 mL) of
HL (22.7 mg, 0.1 mmol) and an aqueous solution (5 mL) of NaN3
(13.1 mg, 0.2 mmol), with stirring. The mixture was stirred for
30 min at room temperature and filtered. Diffraction quality single
crystals of 1 were obtained after a few days by slow evaporation of
the filtrate in open atmosphere. The crystals were isolated, washed
three times with cold MeOH and dried in a vacuum desiccator
* Dr. Zhong-Lu You
Department of Chemistry and Chemical Engineering
Liaoning Normal University
Huanghe Road 850#, Shahekou District
Dalian 116029, P. R. China.
E-mail: youzhonglu@yahoo.com.cn
containing
anhydrous
CaCl2.
Analysis:
Calcd.
for
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Z.-L. You, Q.-Z. Jiao, S.-Y. Niu, J.-Y. Chi
˚
C11H14ClCuN5O: C, 39.88; H, 4.26; N, 21.14 %. Found: C, 40.12;
H, 4.32; N, 21.33 %. Yield: 50.3 % on the basis of HL.
Table 2 Selected bond lengths/A and angles/° for 1 and 2
1
[Cu4L2(CH3COO)2(µ1,1-N3)4] (2). Complex 2 was prepared by the
similar synthetic procedure as described for 1, with
Cu(NO3)2·3H2O replaced by Cu(CH3COO)2·H2O (39.8 mg,
0.2 mmol). Analysis: Calcd. for C26H34Cl2Cu4N16O6: C, 31.49; H,
3.46; N, 22.60 %. Found: C, 31.20; H, 3.53; N, 22.78 %. Yield:
45.9 % on the basis of HL.
Cu1-O1
Cu1-N3
Cu1-N3A
O1-Cu1-N1
N1-Cu1-N3
N1-Cu1-N2
O1-Cu1-N3A
N2-Cu1-N3A
1.911(2)
1.978(2)
2.631(2)
93.0(1)
172.2(1)
84.5(1)
87.6(1)
92.8(1)
Cu1-N1
Cu1-N2
1.950(2)
2.079(2)
O1-Cu1-N3
O1-Cu1-N2
N3-Cu1-N2
N1-Cu1-N3A
N3-Cu1-N3A
89.3(1)
177.5(1)
93.1(1)
87.2(1)
100.3(1)
Caution! Although our samples never exploded during handling,
metal azide complexes are potentially explosive. Only a small
amount of material should be prepared and it should be handled
with care.
2
Cu1-O1
Cu1-O2
Cu1-N3
Cu2-N6A
1.922(5)
1.952(6)
2.464(9)
1.980(7)
2.012(7)
92.7(3)
164.0(3)
84.6(3)
82.9(3)
94.5(3)
164.1(3)
95.2(3)
79.3(3)
95.2(2)
85.4(3)
Cu1-N1
Cu1-N2
Cu2-O3
Cu2-N3
1.941(7)
2.044(7)
1.932(6)
1.991(9)
2.317(6)
91.3(3)
174.2(3)
89.9(3)
101.3(3)
102.7(3)
95.8(3)
Cu2-N6
Cu2-O1
Crystal structure determination
O1-Cu1-N1
N1-Cu1-O2
N1-Cu1-N2
O1-Cu1-N3
O2-Cu1-N3
O3-Cu2-N6A
N6A-Cu2-N3
N6-Cu2-N6A
O3-Cu2-O1
N3-Cu2-O1
O1-Cu1-O2
O1-Cu1-N2
O2-Cu1-N2
N1-Cu1-N3
N2-Cu1-N3
O3-Cu2-N3
O3-Cu2-N6
N3-Cu2-N6
N6A-Cu2-O1
N6-Cu2-O1
X-ray intensities of complexes 1 and 2 were collected using a
Bruker Smart Apex 1000 CCD area detector equipped with graph-
˚
ite-monochromated Mo-KͰ radiation (λ ϭ 0.71073 A) at 298(2) K.
Empirical absorption corrections were applied to the data using the
SADABS program [18]. Structures were solved by the direct
method and refined by full-matrix least squares on F2 using the
SHELXTL version 5.1 [19]. All of the non-hydrogen atoms were
refined anisotropically. All H atoms were placed in calculated posi-
tions and constrained to ride on their parent atoms. The crystallo-
graphic data for the two complexes are summarized in Table 1.
Selected bond lengths and angles are given in Table 2. Crystallo-
graphic data for 1 and 2 have been deposited with the Cambridge
Crystallographic Data Centre (CCDC 614212, 614213).
89.4(3)
174.6(3)
97.0(3)
95.3(3)
the above considerations, we used the tridentate Schiff base
ligand HL to synthesize the complexes. The reason we use
HL as the ligand is that it could adopts versatile coordi-
nation modes through the donor atoms [20, 21]. The second
ligand, viz. azide, is a well known bridging group. It readily
bridges different metal ions through the terminal donor
atoms, forming polynuclear complexes. Copper(II) is a
good candidate of square-pyramidal coordination. Com-
plexes 1 and 2 (as illustated in schemes 1 and 2, respectively)
were synthesized simply under similar synthetic procedures.
The syntheses of the two complexes here demonstrate that
the anions of the copper(II) salts can severely influence the
structures of the complexes.
Results and Discussion
To design novel structures of transition metal complexes,
the ligands used in the synthesis are important. Based on
Table 1 Crystallographical and experimental data for 1 and 2
Compound
Formula
Mr
1
2
C11H14ClCuN5O
331.26
C26H34Cl2Cu4N16O6
991.75
The Schiff base ligand HL was soluble in MeOH. Com-
plexes 1 and 2 are two novel polynuclear complexes. They
are stable in air at room temperature, soluble in DMF,
DMSO, MeOH, EtOH, MeCN and Me2CO; poorly soluble
in water and Et2O.
T /K
298(2)
298(2)
0.71073
Radiation(Mo-KͰ) /λ
Crystal shape/color
Crystal size/mm3
Crystal system
Space group
0.71073
block/blue
0.32ϫ0.29ϫ0.23
orthorhombic
Pbca
6.744(2)
19.885(4)
20.572(4)
90.00
90.00
90.00
2758.8(9)
8
1.595
block/blue
0.27ϫ0.23ϫ0.20
triclinic
¯
P1
˚
a /A
9.829(2)
10.504(2)
10.934(3)
99.285(2)
115.562(2)
102.573(2)
951.3(7)
1
˚
b /A
˚
c /A
Structure description of 1
Ͱ /°
β /°
γ /°
The single-crystal X-ray structural analysis shows that com-
plex 1 is an interesting azide-bridged polynuclear copper(II)
compound. The neutral [CuL(µ1,1-N3)] units in 1 are linked
through the single µ1,1-N3 ligand, forming an infinite one-
dimensional polymeric chain (Scheme 1 and Figure 1). The
Cu atom is five-coordinated by the NNO donor set of the
Schiff base ligand and two bridging azide anions, forming
a square pyramidal coordination. The basal plane of the
square pyramidal coordination is defined by the two
N atoms and one phenolate O atom of L and one terminal
N atom of the bridging azide ligand. The apical position is
occupied by one terminal N atom of the bridging azide
ligand from the symmetry related unit (symmetry code:
3
˚
V /A
Z
Dc /(g/cmϪ3
µ /mmϪ1
F(000)
)
1.731
2.408
500
1.776
1352
θ range/°
Index range (h, k, l)
1.98/27.50
2.16/25.50
Ϫ8/8, Ϫ25/25, Ϫ26/26 Ϫ11/11, Ϫ12/12, Ϫ13/13
Measured reflections
Observed reflections I Ն 2σ(I) 2704
3159
3280
2193
Absorption correction
Min. and max. transmission 0.6003/0.6855
Data/restraints/parameters
Goodness-of-fit on F2
R1, wR2 [I Ն 2σ(I)]
empirical
empirical
0.5625/0.6445
3280/0/247
1.032
0.0808, 0.1943
0.1144, 0.2253
3159/0/174
1.045
0.0281, 0.0697
0.0350, 0.0735
R1, wR2 (all data)
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Azide-bridged Copper(II) Complexes
Figure 2 The molecular packing of 1, viewed along the c axis.
Scheme 1
Figure 3 Molecular structure of 2. Displacement ellipsoids are
drawn at the 30 % probability level and H atoms have been omitted
for clarity. Atoms labeled with the suffix A or unlabeled are at the
symmetry position 1Ϫx, 1 Ϫ y, Ϫ z.
Figure 1 Molecular structure of 1. Displacement ellipsoids are
drawn at the 30 % probability level and H atoms have been omitted
for clarity. Atoms labeled with the suffix A or unlabeled are at the
symmetry position Ϫ1/2 ϩ x, 1/2 Ϫ y, 1 Ϫ z.
graphic a-axis (Figure 2). There are no short intermolecular
contacts among the chains from the crystallographic study.
Ϫ1/2 ϩ x, 1/2 Ϫ y, 1 Ϫ z). Each azide ligand bridges adjac-
ent copper(II) ions through basal-apical linkage mode. The
apical Cu-N bond length is much longer than usual. The
other bond lengths and angles are within normal values.
The Cu···Cu distance is found to be 4.167(2) A. The
Cu-µ1,1-N3-Cu chains are propagated along the crystallo-
Structure description of 2
The single-crystal X-ray structural analysis shows that com-
plex 2 is an interesting acetate- and azide-bridged tetranu-
clear copper(II) compound with inversion centre (Scheme 1
and Figure 3). The asymmetric unit of 2 consists of one
˚
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Z.-L. You, Q.-Z. Jiao, S.-Y. Niu, J.-Y. Chi
half of the molecule, with the other half generated by the
¯
inversion (1) symmetry. Each asymmetric unit is a dinuclear
copper(II) complex moiety, within which the Cu atoms are
connected by three bridging groups: one phenolate O atom,
one µ1,1-N3 ligand, and one acetate ligand. The two asym-
metric units are further linked through another two µ1,1-N3
ligands, forming a tetranuclear copper(II) complex. Each
of the symmetry related two outermost Cu atoms is five-
coordinated by one Schiff base ligand, one bridging azide
ligand, and one bridging acetate ligand, forming a square
pyramidal coordination. The basal plane of the square pyr-
amidal coordination for the outermost Cu atom is defined
by the two N atoms and one phenolate O atom of L and
one O atom of the bridging acetate ligand. The apical posi-
tion is occupied by one terminal N atom of the bridging
azide ligand. Each of the symmetry related two central Cu
atoms is five-coordinated by one phenolate O atom, one
acetate ligand, and three bridging azide ligands, forming a
square pyramidal coordination. The basal plane of the
square pyramidal coordination for the central Cu atom is
defined by the three terminal N atoms from the three bridg-
ing azide ligands and one O atom of the bridging acetate
ligand. The apical position is occupied by the phenolate O
atom of L. Each azide ligand in the asymmetric unit bridges
adjacent copper(II) ions through basal-apical linkage mode,
while the azide ligands located between the symmetry units
bridges the central copper(II) ions only through the basal
linkage mode. The apical Cu-N and Cu-O bond lengths are
much longer than usual. The other bond lengths and angles
are within normal values. The Cu···Cu distances are found
Figure 4 The crystal packing of 2, viewed along the a axis.
cedure, only with different copper(II) salts, viz. copper(II)
nitrate for 1 and copper(II) acetate for 2. The different
anions of the copper(II) salts used in the preparation of
the complexes can severely influence the structures of the
final products.
˚
˚
to be 3.066(2) A for Cu1 and Cu2 and 3.072(2) A for Cu2
and Cu2A, respectively. In the crystal structure, molecules
are stacked along the b axis, with no short intermolecular
contacts (Figure 4).
Acknowledgment. This work was supported by the National Natural
Science Foundation of China (20571037).
I.r. spectra
Complexes 1 and 2 show strong absorption bands at 2054
and 2072 cmϪ1, respectively, consistent with the presence of
azide ligands in the structures. The lower frequency of the
stretching vibration for the azide ligands in 1 than that in
2 may be attributed to the highly asymmetrical nature of
the azide bridges in 1 [22]. The bands corresponding to the
azomethine (CϭN) groups in the complexes appear at 1612
and 1617 cmϪ1 for 1 and 2, respectively [23]. Complex 2
exhibits the typical acetate vibrations νasym(CO2) at
1531 cmϪ1 and νsym(CO2) at 1443 cmϪ1. While for 1, there
are no vibrations for the nitrate groups, indicating that they
were not participate in the coordination.
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