Three [CuL2] type complexes with halogen-substituted schiff base ligands containing a pyridine group

Article abstract of DOI:10.1080/15533174.2010.538027

Three mononuclear Schiff base copper(II) complexes, [Cu(L¹) ₂] (1), [Cu(L³)₂] (2) and [Cu(L ³)₂] (3) (HL¹= 2,4-dichloro-6-[(2-chloro-3- pyridyl)iminomethyl]phenol, HL² = 2,4-dibromo-6-[(2-chloro-3-pyridyl) -iminomethyl]phenol, HL³ = 2-bromo-4-chloro-6-[(2-chloro-3-pyridyl) iminomethyl]phenol), have been synthesized and characterized by elemental analyses, IR, UV-Vis spectra, and X-ray single crystal diffraction. X-ray structures reveal each crystal unit contains two molecules and the coordination environment around the copper(II) atom is tetracoordinated by two Schiff base ligands, showing a tetrahedron geometry with some distortion. Pairs of intermolecular C-H...X (X = Cl or Br), C-H...N and C-H...O hydrogen bonds form many hydrogen bonding rings and play a crucial role in stabilizing the crystal structures. Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15533174.2010.538027

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:155–164, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2010.538027
Three [CuL2] Type Complexes with Halogen-Substituted
Schiff Base Ligands Containing a Pyridine Group
Wen-Kui Dong, Jun-Feng Tong, Yin-Xia Sun, Shang-Sheng Gong and Li Li
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, P. R. China
as a biological catalyst.[9−12] In light of the importance of Schiff
Three mononuclear Schiff base copper(II) complexes, [Cu(L1)2]
(1), [Cu(L2)2] (2) and [Cu(L3)2] (3) (HL1 = 2,4-dichloro-6-[(2-
chloro-3-pyridyl)iminomethyl]phenol, HL2 = 2,4-dibromo-6-[(2-
chloro-3-pyridyl)-iminomethyl]phenol, HL3 = 2-bromo-4-chloro-
6-[(2-chloro-3-pyridyl)iminomethyl]phenol), have been synthe-
sized and characterized by elemental analyses, IR, UV–Vis spectra,
and X-ray single crystal diffraction. X-ray structures reveal each
crystal unit contains two molecules and the coordination environ-
ment around the copper(II) atom is tetracoordinated by two Schiff
base ligands, showing a tetrahedron geometry with some distor-
tion. Pairs of intermolecular C–H· · ·X (X = Cl or Br), C–H· · ·N
and C–H· · ·O hydrogen bonds form many hydrogen bonding rings
and play a crucial role in stabilizing the crystal structures.
base compounds and the copper element, herein, the authors
report the syntheses, characterization and crystal structures of
three Cu(II) complexes 1, 2, and 3 derived from an important
class of Schiff base ligand HL by the condensation of halogen-
substituted salicylaldehyde and 2-chloropyridin-3-amine in 1:1
molar ratio.
EXPERIMENTAL
Materials and Instruments
Commercially available 3,5-dichlorosalicylaldehyde, 3,5-
dibromosalicylaldehyde and 3-bromo-5-chlorosalicylaldehyde
from Acros Organics as well as 2-chloropyridin-3-amine from
Alfa Aesar were purchased. Solvents were AR grade from Tian-
jin Chemical Reagent Factory and used without further purifi-
cation.
Keywords copper(II) complex, crystal structure, property, synthesis,
Schiff base ligand
INTRODUCTION
Elemental analysis for copper was detected by an IRIS
ER/S·WP-1 ICP atomic emission spectrometer. Carbon, hy-
drogen, and nitrogen analyses were carried out with a GmbH
VariuoEL V3.00 automatic elemental analyzer. IR spectra were
recorded on a VERTEX 70 FT-IR spectrophotometer, with sam-
ples prepared as KBr (500 ∼ 4000 cm−1) and CsI (100 ∼
500 cm−1) pellets. UV–Vis spectra were taken on a Shimadzu
UV–240 spectrophotometer. Electrolytic conductance measure-
ments were made with a DDS–11A type conductivity bridge
using a 1.0 × 10−3 mol·L−1 solution in DMF at room tem-
perature. X-ray single crystal structures were determined on a
Bruker Smart APEX CCD area detector. Melting points were
measured by the use of a microscopic melting point appara-
tus made in Beijing Taike instrument limited company, and the
thermometer was uncorrected.
Compounds containing phenoxy-imine groups are a versa-
tile class of ligands that display a truly impressive range of
diverse applications spanning from bioinorganic chemistry to
coordination chemistry, chemical catalysis, and materials re-
lated applications.[1−6] Meanwhile, Schiff base type complexes
play an important role in the development of coordination chem-
istry related to catalysis and enzymatic reactions, magnetism,
and molecular architectures.[7−8] On the other hand, copper el-
ement is very important for human beings and has been know
as an essential bioelement for some time, but its biological role
has been recognized only in the last decades due to the rapid
development of bioinorganic chemistry, a successful interaction
between model complexes and protein biochemistry, as well as
the biological role of copper is primarily in redox reactions and
Syntheses of Schiff base Ligands HL1, HL2, and HL3
The synthetic route for three N, O-bidentate ligands is given
in Scheme 1.
Received 16 January 2010; accepted 19 July 2010.
This work was supported by the Foundation of the Education De-
partment of Gansu Province (No.0904-11) and the ‘JingLan’ Talent
Engineering Funds of Lanzhou Jiaotong University, which are grate-
fully acknowledged.
Address correspondence to Wen-Kui Dong, School of Chemical
and Biological Engineering, Lanzhou Jiaotong University, Lanzhou,
730070, P. R. China. E-mail: dongwk@126.com
2,4-Dichloro-6-[(2-chloro-3-pyridyl)iminomethyl]phenol
(HL1).
To a warm pale-yellow ethanol solution (4 mL) of 3,5-
dichlorosalicylaldehyde (185.3 mg, 0.970 mmol), the colorless
155

156
W.-K. DONG ET AL.
N
O
N
EtOH
R2
OH
R2
OH
H2N
Cl
N
R1
R1
Cl
HL1: R1=3-Cl, R2=5-Cl; HL2: R1=3-Br, R2=5-Br;
HL3: R1=3-Br, R2=5-Cl.
SCH. 1. Syntheses of N, O-bidentate ligands HL1, HL2 and HL3.
ethanol solution (4 mL) of 2-chloropyridin-3-amine (115.4 mg,
1.0 mmol) was added dropwise, and the color of the mixture
turned into brown. The mixture solution was maintained under
reflux for 6 h, and a saffron yellow powder product was obtained.
It was filtered off, washed with ethanol and ethanol/hexane (1:4,
V/V) (3 × 4 mL), respectively, then dried under reduced pres-
sure yielding 0.1396 g powder. Yield, 52%. m.p. 186 ∼ 187◦C.
Anal. calcd. for C12H7Cl3N2O (%): C, 47.8; H, 2.3; N, 9.3.
Found: C, 47.7; H, 2.3; N, 9.4.
Syntheses of Complexes 1, 2, and 3
Complex 1.
A pale-blue ethanol solution (2 mL) of Cu(II) acetate mono-
hydrate (2.5 mg, 0.013 mmol) was added dropwise to a pale-
yellow ethyl acetate solution (4 mL) of HL1 (7.5 mg, 0.026
mmol) at room temperature. The color of the mixing solu-
tion turned to yellow immediately then turned to brown slowly
and the filtrate was allowed to stand at room temperature for
about two weeks. Single crystals suitable for X-ray structural
determination were obtained by the slow evaporation from
ethanol and ethyl acetate solution. Anal. calcd. for [Cu(L1)2]
(C24H12Cl6CuN4O2) (%): C, 43.4; H, 1.8; N, 8.4; Cu, 9.6.
Found: C, 43.3; H,1.8; N, 8.5, Cu, 9.5.
2,4-Dibromo-6-[(2-chloro-3-pyridyl)iminomethyl]phenol
(HL2).
To a warm pale-yellow ethanol solution (4 mL) of 3,5-
dibromosalicylaldehyde (201.9 mg, 0.721 mmol), the colorless
ethanol solution (4 mL) of 2-chloropyridin-3-amine (92.7 mg,
0.721 mmol) was added dropwise, and the color of the mixture
turned into brown. The mixture solution was maintained under
reflux for 8 h, and a white powder product was obtained. It
was filtered off, washed with ethanol and ethanol/hexane (1:4,
V/V) (3 × 4 mL), respectively, then dried under reduced pres-
sure yielding yellow 0.2474 g powder. Yield, 68%. m.p. 169 ∼
170◦C. Anal. calcd. for C12H7Br2ClN2O (%): C, 36.9; H, 1.8;
N, 7.2. Found: C, 36.9; H, 1.7; N, 7.3.
Complex 2.
Complex 2 was synthesized in a similar manner as described
for complex 1. A pale-blue methanol solution (2 mL) of Cu(II)
acetate monohydrate (2.0 mg, 0.010 mmol) was added drop-
wise to a pale-yellow ethanol solution (4 mL) of HL2 (8.0 mg,
0.020 mmol) at room temperature. The color of the mixing
solution turned to yellow immediately then turned to brown
slowly, and the filtrate was allowed to stand at room tempera-
ture for about several weeks. Single crystals suitable for X-ray
structural determination were obtained by the slow evaporation
from methanol and ethanol solution. Anal. calcd. for [Cu(L2)2]
(C24H12Br4Cl2CuN4O2) (%): C, 34.2; H, 1.4; N, 6.7; Cu, 7.5.
Found: C, 34.1; H, 1.3; N, 6.8, Cu, 7.4.
2-Bromo-4-chloro-6-[(2-chloro-3-pyridyl)iminomethyl]phenol
(HL3).
Complex 3.
The synthetic procedure was as similar as that for complex
Complex 3 was synthesized in a similar manner as described
1. To a warm kelly ethanol solution (3 mL) of 3-bromo-5- for complexes 1 and 2. A pale-blue methanol solution (2 mL)
chlorosalicylaldehyde (237.6 mg, 1.001 mmol), the colorless of Cu(II) acetate monohydrate (2.2 mg, 0.011 mmol) was added
ethanol solution (3 mL) of 2-chloropyridin-3-amine (124.2 mg, dropwise to a pale-yellow methanol solution (4 mL) of HL3
0.966 mmol) was added dropwise, and the color of the mixture (7.8 mg, 0.022 mmol) at room temperature. The color of the
turned into yellow. The mixture solution was maintained under mixing solution turned to yellow immediately then turned to
reflux for 8 h, and a white powder product was obtained. It was brown slowly and the filtrate was allowed to stand at room
filtered off, washed with ethanol and ethanol/hexane (1:4, V/V) temperature for about two weeks. Single crystals suitable for
(3 × 4 mL), respectively, then dried under reduced pressure X-ray structural determination were obtained by the slow evap-
yielding jacinth 0.1207 g solid. Yield, 36%. m.p. 168 ∼ 170◦C. oration from methanol solution. Anal. calcd. for [Cu(L3)2]
Anal. calcd. for C12H7BrCl2N2O (%): C, 41.7; H, 2.0; N, 8.1. (C24H12Br2Cl4CuN4O2) (%): C, 38.3; H, 1.6; N, 7.4; Cu, 8.4.
Found: C, 41.6; H, 2.1; N, 8.2.
Found: C, 38.1; H,1.5; N, 7.5, Cu, 8.4.

HALOGEN-SUBSTITUTED SCHIFF BASE COPPER COMPLEXES
157
TABLE 1
Crystal data and structure refinement for complexes 1, 2, and 3
Complex 1
Complex 2
Complex 3
Empirical formula
Formula weight
Temperature (K)
C24H12Cl6CuN4O2
664.62
298(2)
C24H12Br4Cl2CuN4O2
842.46
298(2)
C24H12Br2Cl4CuN4O2
753.54
298(2)
˚
Wavelength (A)
0.71073
0.71073
0.71073
Crystal system
Space group
Monoclinic
P2/c
Monoclinic
P2/c
Monoclinic
P2/c
Unit cell dimensions
˚
a (A)
12.975(2)
8.5647(8)
12.953(1)
90
119.424(1)
90
1253.7(2)
2, 1.761
1.543
13.130(2)
8.688(1)
13.094(2)
90
119.095(2)
90
1305.2(3)
2, 2.144
7.196
12.975(1)
8.681(1)
12.924(1)
90
118.921(2)
90
1274.2(2)
2, 1.964
4.445
˚
b (A)
˚
c (A)
α (◦)
β (◦)
γ (◦)
3
˚
Volume (A )
Z, Dcalc(Mg/m3)
µ (mm−1
F (000)
)
662
806
734
Crystal size (mm)
0.26 × 0.24 × 0.11
1.81 to 25.02
–8 ≤ h ≤ 15, –10 ≤ k ≤
9, –15 ≤ l ≤ 15
0.23 × 0.20 × 0.10
0.18 × 0.17 × 0.07
θ (◦)
1.77 to 25.01
1.79 to 25.02
Limiting indices
–10 ≤ h ≤ 15, –10 ≤ k ≤ 9, –15 ≤ h ≤ 12, –10 ≤ k ≤ 9,
–15 ≤ l ≤ 7
–10 ≤ l ≤ 15
6470/2256 [Rint =0.0338]
25.02, 100.0 %
0.7461, 0.5017
Full-matrix least- squares
on F2
Reflections collected /unique
Completeness to θ
Max. & min. transmission
Refinement method
6100/2129 [Rint =0.0284] 6329/2299 [Rint =0.0643]
25.02, 99.9 %
0.8486, 0.6897
Full-matrix least-squares
on F2
25.01, 99.7 %
0.5331, 0.2884
Full-matrix least- squares
on F2
Data/restraints/parameters
GOF on F2
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
Largest diff. peak and hole (eA
CCDC NO.
2229/0/168
1.040
2299/0/168
0.984
2256/0/168
0.988
0.0310, 0.0644a
0.0485, 0.0774
0.313, –0.326
757716
0.0466, 0.1141b
0.0666, 0.1267
1.059, –1.257
757715
0.0267, 0.0640c
0.0367, 0.0670
0.476, –0.487
757714
−3
˚
)
aw = 1/[σ2(F◦2)+ (0.027P)2+ 1.2614P], bw = 1/[σ2(F◦2)+ (0.0708P)2], cw = 1/[σ2(F◦2)+ (0.0379P)2], where P = (F◦2+ 2Fc2)/3
RESULTS AND DISCUSSION
Data Collection, Structure Determination, and Refinement
Diffraction intensities for the complexes 1, 2 and 3 were col-
lected at 298(2) K using a Bruker SMART APEX II CCD area-
By the condensation of the aldehydes with primary amines,
it can readily give rise to the corresponding Schiff base com-
pounds, which were easily identified by their IR spectra, where
replacement of the carbonyl by the imine group results in lower-
ing of the energy of the ν(C=0) stretch. The Schiff bases prepared
in this way are formed in nearly quantitative yields and are of
high purity. The results of the elemental analyses are in accord
with the composition suggested for the Schiff base ligands and
the three Cu(II) complexes.
˚
detector with MoKα radiation (λ = 0.71073 A). The collected
data were reduced using the SAINT program,[13] and multi-
scan absorption corrections were performed using the SADABS
program.[14] The structures were solved by direct method and re-
fined against F2 by full-matrix least-squares method using the
SHELXTL program.[15] All of the non-hydrogen atoms were
refined anisotropically. H atoms were positioned geometrically
˚
(C–H = 0.93 A) and refined as riding, with Uiso(H) = 1.20
Ueq(C). The crystallographic data and experimental parameters Molar Conductances
relevant to the structure determination for the complexes 1, 2,
and 3 are summarized in Table 1.
Complexes 1, 2, and 3 are soluble in DMF and DMSO,
slightly soluble in CHCl3,but not soluble in DCM, EtOH,

158
W.-K. DONG ET AL.
TABLE 2
The most important FT-IR bands for the ligands and their complexes (cm−1
)
Compound
ν(O−H)
ν(C=N)
ν(Ar−O)
ν(Cu−N)
ν(Cu−O)
ν(C=C) benzene ring skeleton
HL1
3433
–
3425
–
3437
–
1618
1601
1622
1597
1618
1598
1215, 1198
1211, 1193
1245, 1200
1215, 1194
1213, 1197
1211, 1194
–
474
–
473
–
–
430
–
440
–
1554, 1448, 1404
1566, 1414, 1441
1553, 1441, 1421
1564, 1503, 1435
1553, 1444, 1402
1564, 1506, 1435
Complex 1
HL2
Complex 2
HL3
Complex 3
472
422
MeOH, MeCN, THF, acetone, and ethyl acetate. All complexes can be assigned to the π–π* transition of the benzene rings, the
display good stability in air at room temperature. Meanwhile, second one at 307 nm can be assigned to the intra-ligand π–π*
three ligands (HL1, HL2, and HL3) are soluble in aforemen- transition of the C=N bonds, and the third one at 426 nm can
tioned solvents. Molar conductance values of complexes 1, 2, be attributed to the n–π* transition in the free ligand.
and 3 of 1.0 × 10−3 mol · L−1 DMF solutions are 3.3, 2.7 and
Compared with the absorption peaks of the free ligands, the
2.6 S · cm2· mol−1, respectively, indicating these complexes are corresponding absorption peaks at 254, 284, and 400 nm are
non-electrolytes.
observed in complex 1 (244, 283, and 401 nm for complex 2 and
263, 283, and 401 nm for complex 3). Obviously, hypsochromic
shifts of three absorption peaks are ca. 2 ∼ 4, 23 ∼ 25, and 26 ∼
27 nm, respectively. The first value of blue shift is small but the
other two ones are considerable larger up to 25 nm, indicating
the coordination of CuII ions with free ligands via azomethine
nitrogen and phenolic oxygen atoms.
IR Spectra Analyses
Some important IR absorption bands are listed in Table 2.
The IR spectra of the free ligands and their corresponding Cu(II)
complexes show characteristic C=N stretching bands. For the
free ligand HL1, HL2, and HL3, the bands appear at 1618, 1622,
and 1618 cm−1, respectively, while the C=N bands of com-
plexes 1, 2, and 3 are observed at 1601, 1597, and 1598 cm−1
,
Descriptions of Crystal Structures
respectively. The frequency towards to lower wavenumbers of
the C=N absorption shift by ca. 17 ∼ 25 cm−1 because of the
behavior between the free ligands and the corresponding com-
plexes resulting in weakening the force constant of C=N bond.
The Ar–O stretching frequencies appear as a strong band
within the 1245 ∼ 1193 cm−1 range, and the toward lower
wavenumbers of the Ar–O absorption shift by 2 ∼ 30
cm−1indicating that Cu–O bonds are formed between the Cu(II)
ions and the oxygen atoms of the phenolic groups.[16−17] In ad-
dition, the broad OH group absorption bands centered at 3433,
3425, and 3437 cm−1 in the free ligands HL1, HL2 and HL3,
however, in the spectra of complexes 1, 2, and 3 disappear, fur-
ther demonstrating the coordination of deprotonated phenolic
oxygen atom to copper ions.
The X-ray structural studies reveal that the formation
of metal complexes 1, 2, and 3 have 2:1 ligand to metal
stoichiometries, and three complexes all crystallize in the
monoclinic system and P2/c space group. In all cases, the
copper atom is bonded to the oxygen and nitrogen donor
atoms of the two ligand molecules in a trans arrangement
in which the copper ion is four coordinated. The molecular
structures of complexes 1, 2, and 3 are illustrated in Figure 1,
and relevant bond lengths and angles are summarized in Table
4. Three centrosymmetric copper complexes, existing two-fold
axes passing through the copper atom, all have tetrahedron
geometries with some distortion around the central copper
atoms, as shown in Figure. 2, which are different from the
copper complexes coordinated by single-substituent ligands
The IR spectra of complexes 1, 2, and 3 in the region of 500 ∼
100 cm−1 show ν(Cu N) (or ν(Cu O)) vibrational absorption
TABLE 3
frequencies at 474, 472, and 473 (or 430, 440, and 422) cm−1
,
The UV–Vis bands for the ligands and their complexes (nm)
respectively.[18−19] These bands are not observed in the spectra
of corresponding free ligands HL1, HL2 and HL3.
Compound
λ1
λ2
λ3
HL1
258
254
248
244
265
263
307
284
306
283
308
283
426
400
427
401
428
401
UV–Vis Spectra Analyses
Complex 1
The most UV–Vis spectra data of the ligands and complexes
1, 2, and 3 are shown in Table 3. The UV–Vis spectrum of the free
ligand HL1 exhibit three absorption peaks at ca. 258, 307, and
426 nm (248, 306, and 427 nm for HL2 and 265, 308, and 428
nm for HL3), respectively. The first absorption peak at 258 nm
HL2
Complex 2
HL3
Complex 3

HALOGEN-SUBSTITUTED SCHIFF BASE COPPER COMPLEXES
159
TABLE 4
◦
˚
The selected bond lengths (A) and bond angles ( ) for
complexes 1, 2, and 3
Bond distance
Bond angle
Complex 1
Cu(1)–O(1)#1
Cu(1)–O(1)
Cu(1)–N(1)#1
Cu(1)–N(1)
1.892(2) O(1)#1–Cu(1)–O(1)
145.4(1)
1.892(2) O(1)#1–Cu(1)–N(1)#1 93.93(9)
1.975(2) O(1)–Cu(1)–N(1)#1
1.975(2) O(1)#1–Cu(1)–N(1)
O(1)–Cu(1)–N(1)
94.23(9)
94.23(9)
93.93(9)
152.3(1)
N(1)#1–Cu(1)–N(1)
Complex 2
Cu(1)–O(1)#2
Cu(1)–O(1)
Cu(1)–N(1)#2
Cu(1)–N(1)
1.893(4) O(1)#2–Cu(1)–O(1)
1.893(4) O(1)#2–Cu(1)–N(1)#2
1.990(5) O(1)–Cu(1)–N(1)#2
1.990(5) O(1)#2–Cu(1)–N(1)
O(1)–Cu(1)–N(1)
146.1(2)
93.7(2)
94.6(2)
94.6(2)
93.7(2)
151.5(3)
N(1)#2–Cu(1)–N(1)
Complex 3
Cu(1)–O(1)
Cu(1)–O(1)#3
Cu(1)–N(1)
Cu(1)–N(1)#3
1.889(2) O(1)–Cu(1)–O(1)#3
1.889(2) O(1)–Cu(1)–N(1)
1.979(2) O(1)#3–Cu(1)–N(1)
1.979(2) O(1)–Cu(1)–N(1)#3
145.6(1)
93.58(8)
94.80(9)
94.80(9)
O(1)#3–Cu(1)–N(1)#3 93.58(8)
N(1)–Cu(1)–N(1)#3
151.4(1)
Symmetry transformations used to generate equivalent atoms: #1,
#2, and #3 all are –x+1, y, –z+1/2 for complex 1, 2, and 3, respectively.
geometry is square planar too. By contrast, the geometry
of bis-bidentate Schiff base copper(II) complexes can be
the result of steric and electronic effects, which result in
various intermediate geometries between square planar and
tetrahedral.[23−25] Furthermore, each crystal unit of three
complexes is consisting of one divalence Cu(II) ions and two
deprotonated N, O-bidentate L− units.
The coordination environment around the central Cu(II) ion
is tetra-coordinated by two imino nitrogen atoms (N1 and N1#)
and two deprotonated phenolic oxygen atoms (O1 and O1#)
from two deprotonated L− units. The coordination spheres of
complexes 1, 2, and 3 (bond lengths and angles) are compared
in Table 4, and found rather similar. A slight shortening of the
Cu-O bond lengths is observed on passing from complexes 1 ∼
3. These structural features, which favor steric hindrance of the
L− fragments, can account for the distortion of the ligands in
the complexes. Indeed, the dihedral angels between two metal
chelating rings (the plane defined by Cu1N1O1C1C2C3 and the
FIG. 1. The ORTEP views of the crystal structure with thermal ellipsoids
were drawn at the 30% probability for complexes 1, 2, and 3 and hydrogen
atoms have been omitted for clarity.
on the aromatic ring, showing lightly distorted square-planar other plane defined by Cu1N1#O1#C1#C2#C3#) for complexes
coordination spheres.[20−21] Besides, in the analogous {2-[1- 1, 2, and 3 are 42.83(2), 43.96(4), and 44.86(3)◦, respectively.
(2,6-diethylphenylimino)ethyl]phenoxy}2Cu(II), {2-[1-(2,6- The six membered chelate ring formed through O1 and N1
dimethyl-phenylimino)ethyl]phenoxy}2Cu(II) and {2-[1-(2- shows a fold about the O1· · ·N1 vector and Cu1 are displaced
˚
methylphenylimino)ethyl]phenoxy}2Cu(II) complexes where ca 0.400, 0.418, and 0.435 A for respective complexes 1, 2, and 3
a phenyl substituent is attached to the imine nitrogen,[22] the from their corresponding mean-plane of the O1–C1–C2–C3–N1

160
W.-K. DONG ET AL.
group. These observations suggest a variety negative, versus that
of the free HL ligand.
The coordinated bonds Cu1–N1 and Cu1–O1 in com-
plexes 1 ∼ 3, have similar lengths and are in the same
range to those reported for similar Bis{(E)-4-bromo-2-[(2-
chloro-3-pyridyl)- iminomethyl]phenolato-κ2N, O} copper(II)
and Bis{(E)-4-chloro-2-[(2-chloro-3-pyridyl)imino-methyl-
κN]phenolato-κO} copper(II) complexes, i.e., Cu–N distances
˚
in the range 1.972(3) to 1.994(3) A, while Cu–O distances have
values between 1.882(2) to 1.897(3) A.[20−21] Owing to the pres-
˚
ence of the distortion the for N–Cu–O bond angles at the copper
center in all complexes are also marginally different from the
ideal value of 90◦ [O(1)–Cu(1)–N(1) and O(1)#–Cu(1)–N(1) are
93.93(9)◦ and 94.23(9)◦ for complex 1; 93.7(2)◦ and 94.6(2)◦
for complex 2; 93.58(8)◦ and 94.80(9)◦ for complex 3], while
the diagonal angles [O(1)#–Cu(1)–O(1) and N(1)#1–Cu(1)–N(1)
are 145.4.1(1)◦ and 152.3(1)◦ for complex 1; 146.1(2)◦ and
151.5(3)◦ for complex 2; 145.6(1)◦ and 151.4(1)◦ for complex
3] are also significantly deviated from the expected value of
180◦. It is worthy to note that there exist similar bond distances
and bond angles among three copper complexes, suggesting
the different substituted groups on the aromatic ring having al-
most no effect on the coordination of the copper complexes.
Interestingly, the dihedral angels between aromatic ring and
pyridine ring for complexes 1, 2, and 3 are 70.64(3), 71.73(2),
and 73.05(5)◦, respectively, indicating that substituted pyridine
group in the complexes have a weaker steric crowding in order
to form centrosymmetric compounds.
For complex 1, as shown in Figure 3, four pairs of inter-
molecular C–H· · ·Cl, C–H· · ·O and C–H· · ·N hydrogen bonds
(Table 5) linked adjacent four complex 1 molecule units into
a tetra-polymeric structure. Besides, a pair of C12–H12· · ·Br2
hydrogen bonding interaction between carbon of the pyridine
ring and the substituted chlorine group on the aromatic ring
produces a twenty-six membered ring with a graph motif of
R22(26). Two intermolecular C10–H10···O1 and C11–H11···O1
hydrogen bonds between aromatic carbon and phenolic oxygen
also form a seven membered ring with a graph motif of R22(7).
Furthermore, a pair of C1–H1· · ·N2 hydrogen bonds between
azomethine carbon and pyridine nitrogen also form a twelve-
membered ring with a graph motif of R22(12). Above-mentioned
hydrogen bonds play an import role in stabilizing the crystal
structure. In conclusion, with the help of hydrogen bonds and
van der Waals forces, the packing diagrams of complex 1 show a
network-like structure along the b axis, and form an intramolec-
ular hexagon cave occupying the central position of the unit
cell between neighboring molecular layers via carbon atom and
chlorine atom along the c axis, as illustrated in Figure 4.
For complex 2, in Figure 5, three pairs of intermolecular
C–H· · ·Br, C–H· · ·O and C–H· · ·N hydrogen bonds (Table
5) linked adjacent other four complex 2 molecule units into a
tetra-polymeric structure. Similar to complex 1, two pairs of
C12–H12· · ·Br2 and C1–H1· · ·N2 hydrogen bonds can also
FIG. 2. The diagrams showing the coordination geometries around the Cu
ion for complexes 1, 2, and 3. (Figure is provided in color online.)

HALOGEN-SUBSTITUTED SCHIFF BASE COPPER COMPLEXES
161
TABLE 5
◦
˚
Hydrogen bonding distances (A) and bond angles ( ) for three complexes
D–H· · ·A
Complex 1
D–H
H· · ·A
D· · ·A
D–H· · ·A
Symmetry code
C1–H1· · ·N2
C10–H10· · ·O1
C11–H11· · ·O1
C12–H12· · ·Cl2
Complex 2
0.93
0.93
0.93
0.93
2.80
2.66
2.62
2.83
3.176 (4)
3.513 (4)
3.457 (4)
3.733 (3)
106
152
150
165
1 − x, 1 − y, −z
x, −y, −1/2 + z
1 − x, −y, −z
−1 + x, y, −1 + z
C12–H12· · ·Br2
C1–H1· · ·N2
C11–H11· · ·O1
Complex 3
0.93
0.93
0.93
2.96
2.80
2.68
3.874 (4)
3.203 (7)
3.514 (7)
169
108
150
−1 + x, y, −1 + z
1 − x, 1 − y, −z
1 − x, − y, −z
C1–H1· · ·N2
C10–H10· · ·O1
C11–H11· · ·O1
C12–H12· · ·Cl1
0.93
0.93
0.93
0.93
2.77
2.71
2.64
2.88
3.164 (4)
3.558 (3)
3.464 (4)
3.798 (3)
107
152
148
170
1 − x, 2 − y, 1 − z
x, 1 − y, 1/2 + z
1 − x, 1 − y, 1 − z
1 + x, y, 1 + z
described as graph motifs of R22(26) and R22(12). Furthermore,
a pair of C10–H10· · ·O1 hydrogen bonds between aromatic
carbon and phenolic oxygen produce an eighteen membered
ring with a graph-motif of R22(18). As shown in Figure 6, the
packing diagram of complex 2 shows the stacking structures is
similar to those of complex 1.
For complex 3, as shown in Figure 7, four pairs of inter-
molecular C–H· · ·Cl, C–H· · ·O and C–H· · ·N hydrogen bonds
FIG. 3. The diagram showing intermolecular hydrogen bonds in complex 1. (Figure is provided in color online.)

162
W.-K. DONG ET AL.
FIG. 4. The packing diagram along the c-axis for complex 1. (Figure is provided in color online.)
FIG. 5. The diagram showing intermolecular hydrogen bonds in complex 2. (Figure is provided in color online.)
FIG. 6. The packing diagram along the c-axis for complex 2. (Figure is provided in color online.)

HALOGEN-SUBSTITUTED SCHIFF BASE COPPER COMPLEXES
163
FIG. 7. The diagram showing intermolecular hydrogen bonds in complex 3. (Figure is provided in color online.)
(Table 5) also linked adjacent four complex 3 molecule units phenolic oxygen produce a seven membered ring with a graph-
into a tetra-polymeric structure. Similar to complexes 1 and motif of R22(7). The packing diagram of complex 3 also shows
2, two pairs of C12–H12· · ·Br2 and C1–H1· · ·N2 hydrogen an infinite regular network structure along the b axis, and form a
bonds can be described as graph motifs of R22(26) and R22(12). centrosymmetric rectangle-like large cave structure via carbon,
Meanwhile, intermolecular C10–H10···O1 and C11–H11···O1 oxygen, bromine, and copper atoms along the c axis of the unit
hydrogen bonding interactions between aromatic carbon and cell, as shown in Figure 8.
FIG. 8. The packing diagram along the c-axis for complex 3. (Figure is provided in color online.)

164
W.-K. DONG ET AL.
9. Selmeczi, K.; Re´glier, M.; Giorgi, M.; Speier, G. Catechol oxidase activity
CONCLUSION
of dicopper complexes with N-donor ligands. Coord. Chem. Rev. 2003, 245,
191–201.
10. Zhou, X.G.; Huang, J.S.; Zhou, Z.Y.; Cheung, K.K.; Che, C.M. Ligand
chirality-controlled selective formation of mono- and dinuclear copper com-
plexes. Inorg. Chim. Acta 2002, 331, 194–198.
11. Poul, N.L.; Campion, M.; Douziech, B.; Rondelez, Y.; Clainche, L.L.; Rein-
aud, O.; Mest, Y.L. Monocopper center embedded in a biomimetic cavity:
From supramolecular control of copper coordination to redox regulation. J.
Am. Chem. Soc. 2007, 129, 8801–8810.
12. Musie, G.T.; Li, X.; Powell, D.R. Synthesis, crystal structure and redox
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13. Bruker. SMART and SAINT.; Bruker AXS Inc.: Madison, Wisconsin, USA,
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15. Sheldrick, G.M. SHELXTL V5.1 Software Reference Manual; Bruker AXS,
Inc.: Madison, USA.
In a summary, a series of new three copper complexes,
bearing a 2:1 ligand:metal stoichiometry, have been syn-
thesized from respective ligands, 2,4-dichloro-6-[(2-chloro-3-
pyridyl)iminomethyl]phenol (HL1), 2,4-dibromo-6-[(2-chloro-
3-pyridyl)iminomethyl]phenol (HL2) and 2-bromo-4-chloro-6-
[(2-chloro-3-pyridyl)iminomethyl]phenol (HL3), by the reac-
tions with Cu(OAc)2·H2O in moderate to high yields. It is
interesting that each copper metal in three complexes is tetra-
coordinated by two Schiff base ligands and the distance of Cu–N
is longer than that of Cu–O. Besides, there exist many hydro-
gen bonds that link adjacent molecules into polymeric structure
showing many cavities. However, the substituted groups on the
aromatic ring or pyridyl ring could play a small impact on the
coordination geometries.
16. Kulkarni, V.H.; Patil, B.R.; Prabhakar, B.K. IR and Mo¨essbauer studies of
Sn(IV) complexes with branched tetradentates containing N and O donor
centres. J. Inorg. Nucl. Chem. 1981, 43, 17–21.
17. Asadi, M.; Jamshid, K.A..; Kyanfar, A.H. Synthesis, characterization and
equilibrium study of the dinuclear adducts formation between nickel(II)
Salen-type complexes with diorganotin(IV) dichlorides in chloroform. In-
org. Chim. Acta. 2007, 360, 1725–1730.
18. Fujita, J.; Martell, A.E.; Nakamoto, K. Infrared spectra of metal chelate
compounds. IV. A normal coordinate treatment of oxalate metal complexes.
J. Chem. Phys. 1962, 36, 324–331.
19. Sen, S.; Talukder, P.; Dey, S.K.; Mitra, S.; Rosair, G.; Hughes, D.L.;
Yap, G.P.A.; Pilet, G.; Gramlich, V.; Matsushita, T. Ligating proper-
ties of a potentially tetradentate Schiff base [(CH3)2NCH2CH2N=CH-
C6H3(OH)(OMe)] with zinc(II), cadmium(II), cobalt(II), cobalt(III) and
manganese(III) ions: synthesis and structural studies. Dalton Trans. 2006,
1758–1767.
SUPPLEMENTARY MATERIALS
Crystallographic data have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary publica-
tion, No. CCDC 757716, 757715 and 757714 for complexes 1,
2, and 3. Copies of the data can be obtained free of charge on ap-
plication to CCDC, 12 Union Road, Cambridge CB21EZ, UK
(Telephone: (44) 01223 762910; Fax: +44-1223-3360 33; E-
mail: deposit@ccdc.cam.ac.uk). These data can be also obtained
free of charge at www.ccdc.cam. ac.uk/conts/retrieving.htm
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