Supramolecular copper(II) complexes of novel Schiff bases derived from β-amino acid and salicylaldehyde: Syntheses, crystal structure, and magnetic property

Article abstract of DOI:10.1016/j.ica.2014.01.007

Two new ternary mixed-ligand complexes [Cu₂(L¹) ₂(bipy)(EtOH)₂] (1) (H₂L¹ = β-phenylal-anine, N-[1-(2-hydroxyphenyl)propylidene], bipy = 4,4′-bipyridine, EtOH = ethanol) and [CuL²(imi)] (2) (H ₂L² = β-(2-chlorophenylal)anine, N-[1-(2- hydroxyphenyl)propylidene], imi = imidazole) have been synthesized and characterized by X-ray diffraction. In 1, the coordination geometry around the copper is square-pyramidal. The Schiff base ligand L¹ coordinates to the Cu(II) ion in a tridentate mode, while the bipyridine ligand coordinates in bidentate bridging mode linking two adjacent Cu(II) ions. The binuclear unit are further linked by hydrogen bond to form a 2D wave-like supramolecular architecture. In 2, the coordination geometry around the copper is distorted square-planar. In the solid state, the imidazole ring is hydrogen-bonded to the carboxyl group, thus linked the two adjacent CuL²(imi) units together with a Cu-Cu distance of 3.515 A?. Magnetic behaviors of complex 1 and 2 exhibit antiferromagnetic interactions within the Cu(II) dimer fitted by the spin Hamiltonian H = -JS₁S₂.

Full text of DOI:10.1016/j.ica.2014.01.007

Inorganica Chimica Acta 413 (2014) 84–89
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Supramolecular copper(II) complexes of novel Schiff bases derived
from b-amino acid and salicylaldehyde: Syntheses, crystal structure,
and magnetic property
⇑
Ya-jin Yan, Fei Yin, Jing Chen, Hang-Li Zhang, Bian-Ling Yan, Yin-Zhi Jiang, Yang Zou
Chemistry Department, Zhejiang Sci-Tech University, 310018 Hangzhou, PR China
a r t i c l e i n f o
a b s t r a c t
Two new ternary mixed-ligand complexes [Cu2(L1)2(bipy)(EtOH)2] (1) (H2L1 = b-phenylal-anine,
N-[1-(2-hydroxyphenyl)propylidene], bipy = 4,40-bipyridine, EtOH = ethanol) and [CuL2(imi)] (2)
(H2L2 = b-(2-chlorophenylal)anine, N-[1-(2-hydroxyphenyl)propylidene], imi = imidazole) have been
synthesized and characterized by X-ray diffraction. In 1, the coordination geometry around the copper
is square-pyramidal. The Schiff base ligand L1 coordinates to the Cu(II) ion in a tridentate mode, while
the bipyridine ligand coordinates in bidentate bridging mode linking two adjacent Cu(II) ions. The binu-
clear unit are further linked by hydrogen bond to form a 2D wave-like supramolecular architecture. In 2,
the coordination geometry around the copper is distorted square-planar. In the solid state, the imidazole
ring is hydrogen-bonded to the carboxyl group, thus linked the two adjacent CuL2(imi) units together
with a Cu–Cu distance of 3.515 Å. Magnetic behaviors of complex 1 and 2 exhibit antiferromagnetic
interactions within the Cu(II) dimer fitted by the spin Hamiltonian H = ꢀJS1S2.
Article history:
Received 13 July 2013
Received in revised form 19 December 2013
Accepted 8 January 2014
Available online 16 January 2014
Keywords:
Copper complex
b-Amino acid
Schiff-base
Self-assembly
Magnetic
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
or monodentate carboxylate bridges [6]; and (d) a 2D network with
metal ions linked by phenoxyl O atom and syn–anti carboxylate
The design and construction of transition metal supramolecular
complexes with amino-acid-based Schiff bases have attracted great
interest, not only because of their potential applications in magne-
tism, asymmetric catalysis, luminescent probes, and biological
functional materials, but also for the tremendous structural diver-
sity of these complexes [1,2]. In general, coordination supramolec-
ular complexes can been assembled through two major chemical
processes: coordinate chemistry and supramolecular chemistry
group [7]. Meanwhile, amino acids are naturally potential candi-
dates for hydrogen-bonded supramolecular networks because the
amino groups and carboxylate groups of amino acids are excellent
hydrogen bond donors and acceptors [8]. Numerous studies have
been directed at supramolecular assembly of amino acid Schiff
bases (or reduced amino acid Schiff bases), they are mainly de-
voted to simple amino acids such as glycine [9–13], valine
[13,14], phenylalanine [13,15–17], etc. Comparatively, studies
involving functional b-amino acids are significantly less explored.
b-Amino acid Schiff base ligand can form two 6-membered chelate
(e.g. strong hydrogen bonds, C–H hydrogen bonds,
p–p stacking
interactions, etc.) [3]. The majority of amino-acid-based Schiff
bases applied so far are derived from a condensation reaction of
salicylaldehyde (or its derivatives) with amino acids, which con-
tain a phenoxyl oxygen atom, an imine nitrogen atom and carbox-
ylate group. Based on the coordination modes, the coordination of
these ONO tridentate ligands with metal ions usually generate the
following types of complexes: (a) mononuclear unit with the car-
boxylate group, using a monodentate mode [4]; (b) multinuclear
complexes with metal centers bridged by phenoxyl O atom, syn–
anti carboxylate anion, or a functional group in the side chain of
the L ligand [5]; (c) 1D helical/zigzag chains via syn–anti, anti–anti,
rings when coordinates with metal, while a-amino acid Schiff base
ligand usually forms one 6-membered and one 5-membered che-
late ring. The introduction of the b-amino acid in the Schiff base li-
gand should not be expected to augment their metal binding
capabilities but may enhance the tendency of the formation of sta-
ble secondary structures [18].
On the other hand, copper is an element with relevant oxidation
states in the first-row transition metal, and its amino Schiff base
complexes with imidazole, pyrazole, pyridine, Phenanthroline
(bipyridine) etc. as coligands have been received much attention.
The products have been investigated by ESR and their magnetism,
catalytic and redox activities have also been tested [19]. Mean-
while, 4,40-bipyridine generally coordinates in bridging fashion,
⇑
Corresponding author. Tel.: +86 571 86843230.
E-mail address: zouyang@zstu.edu.cn (Y. Zou).
http://dx.doi.org/10.1016/j.ica.2014.01.007
0020-1693/Ó 2014 Elsevier B.V. All rights reserved.

Y.-j. Yan et al. / Inorganica Chimica Acta 413 (2014) 84–89
85
measured is off 1.4% from the calcd one, which may be due to
the sample absorbed small amount of water from air.); 1H NMR
in D2O (ppm), 3.06 (2H, d), 4.98 (1H, t), 7.19-7.25 (2H, m), 7.42–
7.51 (3H, m), 7.71 (1H, t), 7.79–7.83 (2H, m), 8.77 (1H, s); IR (KBr
pellet, cmꢀ1): 3421 (br), 1629 (vs), 1600 (s), 1508 (s), 1413 (s),
1384 (s), 1276 (w), 1220(s), 1053 (w), 835 (m), 758 (m); UV–Vis
[5 mM, nm (intensity)]: 200 (1.82), 208 (1.05), 315 (0.325).
2.2.2. [Cu2(L1)2(bipy)(EtOH)2], (1)
To the ethanol solution (150 mL) of H2L1 ligand (1.372 g,
5 mmol), Cu(NO3)2ꢁ3H2O (1.206 g, 5 mmol) was added, then 4,40-
bipyridine (0.782 g, 5 mmol) was added. After stirring at room
temperature for 2 h, the solution was filtered. The filtrate was al-
lowed to evaporate slowly at room temperature. After about one
week green crystals suitable for X-ray crystal analysis were ob-
tained. Yield 33%. (Anal. Calc. for C46H48O8N4Cu2: C, 60.6; H, 5.3;
N, 6.1. Found: C, 60.1; H,5.4; N, 6.1%.) IR (KBr pellet, cmꢀ1): 3429
(w), 1672 (s), 1616 (vs), 1531 (m), 1450 (s), 1415 (m), 1371 (m),
1307(m), 1226 (w), 1156 (m), 1074 (w), 921 (w), 752 (m), 706
(w), 636 (m). UV–Vis [5 mM, nm (intensity)]: 205 (1.82), 216
(1.49), 374 (0.30), 600 (0.05).
Scheme 1. Schematic representation of ligands H2L1 and H2L2.
which usually gives rise to extended metal-ligand structures with
linear 4,40-bipyridine acting as a spacer.
In this paper, we report the synthesis of new ligand H2L2 (b-(2-
chlorophenylal)anine,
N-[1-(2-hydroxyphenyl)propylidene]
Scheme 1) and characterization of two Cu(II) complexes of b-ami-
no-acid-based Schiffbase: [Cu2(L1)2(bipy)(EtOH)2] 1 and [CuL2(imi)]
2 (bipy = 4,40-bipyridine, EtOH = ethanol and imi = imidazole).
2. Experimental
2.2.3. [Cu L2(imi)], (2)
To the ethanol solution (200 mL) of H2L2 ligand (1.545 g,
5 mmol), Cu(NO3)2ꢁ3H2O (1.210 g, 5 mmol) was added, then imid-
azole (0.343 g, 5 mmol) was added. After stirring at room temper-
ature for 2 h, the solution was filtered. The filtrate was allowed to
evaporate slowly at room temperature. After about one week green
crystals suitable for X-ray crystal analysis were obtained. Yield
63%. (Anal. Calc for C19H16O3N3ClCu: C, 52.8; H, 3.7; N, 9.7%. Found:
C, 52.7; H, 3.7; N, 9.7%.) IR (KBr pellet, cmꢀ1): 3427 (w), 1638 (s),
1614 (vs), 1535 (m), 1450 (s), 1401 (m), 1325 (m), 1198 (w),
1148 (m), 1090 (w), 924 (w), 755 (m), 671 (w). UV–Vis [5 mM,
nm (intensity)]: 199 (2.72), 212 (1.16), 362 (0.33), 650 (0.11).
2.1. Materials and methods
All chemicals were of reagent grade and were used as supplied
by commercial sources. FT-IR spectra were measured from KBr pel-
lets using a Nicolet FT-IR 400 system in the range of 4000–
400 cmꢀ1. The 1H NMR spectra was recorded on an Avance AV
400 MHz Digital FT-NMR Spectrometer at room temperature in
D2O. Elemental microanalyses (EA) were performed on a Perkin-El-
mer CHN-2400 analyzer. PXRD data were recorded using a Bruker
D8 system with Cu K
a radiation (k = 0.15405 nm). Thermal gravi-
metric analysis (TGA) were performed using a Perkin Elmer series
7 instrument in N2 flowing with a heating rate of 10 °C minꢀ1. The
temperature-dependent magnetic susceptibility of 1 was mea-
sured with crystalline powder samples on a Quantum Design
MPMS XL-7 Squid magnetometer in a magnetic field of 1000Oe un-
der the temperature range 2–300 K. The diamagnetic contributions
of the samples were corrected by using Pascal’s constants. Single
crystal X-ray diffraction data was collected on a Bruker SMART APEX
CCD-based X-ray diffractometer equipped with a normal focus Mo-
target X-ray tube (k) 0.71073 Å). Details of structure analysis are
described below.
2.3. X-ray Crystallography analysis
Intensities of reflections were measured by using graphite
monochromatized Mo K
a radiation (k = 0.71073 Å) at 293(2) K.
Multi-scan absorption corrections were applied by using SADABS
program.[21] The structure was solved by direct methods. The Cu
atoms were located from E-maps and the other non-hydrogen
atoms were obtained in successive difference Fourier syntheses.
The final refinement was performed by full-matrix least-squares
methods on F2 by the SHELXL-97 program package.[22] All non-
hydrogen atoms were treated anisotropically. The H atom of O–H
was refined with distance restraint of O–H = 0.82 Å and Ui-
so(H) = 1.5 Ueq(O). Other H atoms were positioned geometrically
and constrained as riding atoms with C–H = 0.93–0.98 Å and N–
H = 0.86 Å, Uiso(H) = 1.2Ueq(C,N). Crystallographic data and exper-
imental details for structural analysis are summarized in Table 1.
Selected bond lengths and angles are listed in Tables 2 and 3.
2.2. Synthesis
2.2.1. Ligand H2L1 and H2L2 synthesis
H2L1: The ligand H2L1 was prepared by condensing DL-b-phen-
ylalanine and salicylaldehyde according to the reported procedure
[20]. Yield 87%. (Anal. Calc. for C16H14O3NLi: C, 69.8; H, 5.1; N, 5.1.
Found: C, 69.5; H, 5.2; N, 5.0%.); IR (KBr pellet, cmꢀ1): 3369 (br),
1655 (vs), 1601 (s), 1528 (s), 1450 (m), 1423 (s), 1353 (w), 1226
(w), 1175 (w), 892 (w), 775(m), 661(w); UV–Vis [5 mM, nm (inten-
sity)]: 202 (2.78), 211 (2.16), 366 (0.325).
3. Results and discussion
H2L2: Ligand H2L2 was prepared as for H2L1: DL-b-(2-chloro-
phenyl)alanine (2.01 g, 10 mmol) was dissolved in refluxing meth-
anol (60 mL) containing LiOHꢁH2O (0.42 g, 10 mmol). After cooling
3.1. Description of the crystal structure of [Cu2(L1)2(bipy)(EtOH)2], (1)
A perspective view of [Cu2(L1)2(bipy)(EtOH)2] binuclear com-
plex, showing the atomic numbering scheme, is depicted in Fig. 1.
In the solid state, the copper coordination geometry can be de-
scribed as distorted square-pyramidal geometry. Copper forms
two 6-membered chelate rings with the tridentate ligand, which is
similar to the previously reported complex [Cu2(L1)2 (imi)2] [20].
The ONO donor set of Schiff base ligand [Cu(1)–N(1) = 1.965(5) Å,
Cu(1)–O(1) = 1.909(4) Å, Cu(1)–O(2) = 1.947(4) Å] and one nitrogen
to room temperature,
a solution of salicylaldehyde (1.22 g,
10 mmol) in methanol (20 mL) was added slowly with stirring.
After stirring at room temperature for 1 h, the volume was reduced
to ca. 10 mL in vacuum. Anhydrous ether 200 mL was added to pre-
cipitate the product. The product was isolated as an off-white solid.
Yield 2.78 g, 90%. (Anal. Calc. for C16H13O3NCl2Li C, 55.7; H, 3.8; N,
4.1. Found: C, 54.3; H, 4.0; N, 4.0%. The percentage of carbon

86
Y.-j. Yan et al. / Inorganica Chimica Acta 413 (2014) 84–89
Table 1
O(1)–Cu(1)–O(2) angle of 173.52(18)° is nearly linear. Angular dis-
Crystal structure parameters for the complexes 1 and 2.
tortions in the square plane are also caused by different bite angles
in the 6-membered chelate rings. Thus, the angles O(2)–Cu(1)–
N(1) = 93.08(16)° and O(1)–Cu(1)–N(1) = 92.65(17)° are greater
than the ideal value of 90°. The two pyridine rings of the 4,40-bipyr-
idine molecule is coplanar, and 4,40-bipyridine acts as a bridge
ligand linking the two adjacent Cu(II), with the Cu–Cu distance
11.220 Å. Comparatively in [Cu2(L1)2 (imi)2], the carboxylate group
of the ligand but not the imidazole, link two copper centers to form
the binuclear complex [20].
The hydrogen atom of ethanol (H(1sa)) are involved in hydro-
gen bond with the carboxylic oxygen (O(3)) of the Schiff-base li-
gand. The Hꢁ ꢁ ꢁO distance is 1.910 Å. As shown in Fig. 2, the
binuclear molecular unit is linked with adjacent four units by
intermolecular hydrogen bond (O(1s)–H(1sa)ꢁ ꢁ ꢁO(3)#1 symmetry
code #1: x, ꢀy + 1/2, z + 1/2) to formed a two dimensional wave-
like structure, which can be simplified as a (4,4) network. The 2D
CCDC deposit no.
CCDC-876705
46H48O8N4Cu2
911.98
293
monoclinic
P21/c
CCDC-936230
Empirical formula
Formula weight
T (K)
Crystal system
Space group
Unit cell dimensions
a (Å)
C
C19H16N3O3ClCu
433.35
293
triclinic
ꢀ
P1
13.069(7)
18.498(9)
9.184(5)
9.197(3)
9.590(3)
11.440(4)
66.02(1)
86.44(1)
77.15(1)
898.4(5)
2
b (Å)
c (Å)
a
(°)
b (°)
106.012(7)
c
(°)
V/Å3
2134.1(2)
2
1.419
1.055
Z
Dc (g cmꢀ3
)
1.602
1.390
442
Absorption coefficient (mmꢀ1
F(000)
)
948
structure is further stabilized by
p–p stacking interactions with
Crystal size (mm)
h (°)
Tot., Uniq. Data, Rint
Goodness-of-fit (GOF) on F2
Data/restraints/parameters
0.20 ꢂ 0.20 ꢂ 0.10
0.15 ꢂ 0.10 ꢂ 0.10
interplanar distance of 3.5291(3) Å, and the slip angle of 10.671°.
2.6–25.0
2.0–25.0
10605, 3734, 0.071 4505, 3104, 0.042
1.06
3.2. Description of the crystal structure of [Cu L2(imi)] (2)
1.00
3734/0/272
R1 = 0.0698,
wR2 = 0.1741
R1 = 0.1075,
wR2 = 0.1997
0.66, ꢀ0.77
3104/0/244
R1 = 0.0542,
wR2 = 0.0850
R1 = 0.1181,
wR2 = 0.0903
0.48, ꢀ0.31
Final R indices [I > 2
r(I)]
The racemic [Cu L2(imi)] (2) shows a mildly distorted square-
planar geometry and also forms two 6-membered chelate rings
with the ligand (Fig. 3). Tridentate ONO donor set of L2 ligand
[Cu(1)–N(1) = 1.959(4) Å, Cu(1)–O(1) = 1.906(3) Å, Cu(1)–O(2)
= 1.933(3) Å] and the N(2) [Cu(1)–N(2) = 1.971(4) Å] of imidazole
occupy the corners of a square. The values 1.487(6) Å for the
C(8)–N(1) bond, short than the usual C–N single bond and
1.300(6) Å for double bond [C(7)–N(1)]. A slight distortion in the
square-planar environment of CuII is indicated by the observed
bond angles, which vary from 86.64(17) to 93.94(17)°. The O(1)–
Cu(1)–O(3) angle of 173.41(16)° is nearly linear. The phenyl ring
[C(1)–C(6)] and the ring of C(1), C(6), C(7), N(1), O(1), Cu(1) chelate
ring are almost coplanar with a small dihedral angle of 0.7°. In the
solid state, the imidazole ring is hydrogen-bonded to the carboxyl
group of the adjacent ligand, thus linked the two CuL2(imi) units
together with a Cu–Cu distance of 3.515 Å (Fig. 4). The coordina-
tion mode and structure of 2 is similar to that found in previously
reported one [25], except that the substituent on the b site of the
amino acid is 4-chlorophenyl rather than 2-chlorophenyl.
R indices (all data)
Largest difference in peak and
hole (e Åꢀ3
)
Table 2
Selected bond lengths (Å) and angles (°) for the complex 1.
Bond lengths (Å)
Cu(1)–O(1)
Cu(1)–N(1)
Cu(1)–O(1S)
1.909(4)
1.965(5)
2.526(5)
1.473(7)
Cu(1)–O(2)
Cu(1)–N(2)
N(1)–C(7)
1.947(4)
2.045(5)
1.298(7)
N(1)–C(8)
Bond angles (°)
O(1)–Cu(1)–O(2)
O(1)–Cu(1)–N(2)
O(2)–Cu(1)–N(1)
O(2)–Cu(1)–O(1S)
O(1S)–Cu(1)–N(1)
173.52(18)
88.33(17)
93.08(16)
87.33(15)
90.34(19)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–O(1S)
O(2)–Cu(1)–N(2)
N(1)–Cu(1)–N(2)
O(1S)–Cu(1)–N(2)
92.65(17)
89.63(16)
87.25(15)
160.8(2)
108.91(19)
3.3. Thermogravimetric Analysis (TGA) and Powder X-ray diffraction
(PXRD)
Table 3
Selected bond lengths (Å) and angles (°) for the complex 2.
Bond lengths (Å)
Cu(1)–O(1)
Cu(1)–N(1)
N(1)–C(8)
Bond angles (°)
O(1)–Cu(1)–O(2)
O(1)–Cu(1)–N(2)
O(2)–Cu(1)–N(1)
The thermal stability of the water clusters was studied by the
thermogravimetric (TG) analysis of freshly grown air-dried crystals
of 1 (Fig. S1). The first weight loss of 10.6% in the temperature
range 90–225 °C corresponds to loss of ethanol molecules (calcu-
lated 10.1%). Decomposition of the framework is observed above
295 °C. For 2, TGA display a one-step weight loss above 270 °C.
The similarity of the powder X-ray diffraction (PXRD) pattern of
1 and 2 together with the simulated PXRD pattern from the single
crystal structure, as shown in Fig. S2, suggests the consistency of
the powder sample.
1.906(3)
1.959(4)
1.487(6)
Cu(1)–O(2)
Cu(1)–N(2)
N(1)–C(7)
1.933(3)
1.971(4)
1.300(6)
173.41(16)
86.64(17)
92.56(17)
O(1)–Cu(1)–N(1)
O(2)–Cu(1)–N(2)
N(1)–Cu(1)–N(2)
93.94(17)
87.16(17)
170.24(18)
atom of 4,40-bipyridine [Cu(1)–N(2) = 2.045(5) Å] occupy the cor-
ners of a square while one oxygen atom from ethanol occupy the
apical position [Cu(1)–O(1s) = 2.526(5) Å. This bond length is simi-
lar to those reported in literature [23]. The values 1.473(7) Å for
C(8)–N(1) bond shorter than the usual C–N single bond and the dou-
ble bond C(7)–N(1) length of 1.298(7) Å agree well with the values
of Schiff Base type I described by Ueki et al. [24]. The slight distortion
in square-pyramidal geometry of Cu(II) can be attributed to the
rigidity of the organic ligand and the strong steric effect between
the phenyl rings and the oxygen atoms around the metal. The Cu(II)
atom ligating at the basal positions is located by 0.18 Å above the
least-square plane defined by the basal four ligating atoms. The
3.4. IR spectrum and electronic spectrum
The IR spectrum of complexes 1 and 2 is consistent with the
structural data presented in this work.
In the Schiff base, C@N occurs at 1655 cmꢀ1 for ligand H2L1
(1629 cmꢀ1 for H2L2). After complexation with Cu(II), C@N shifts
to lower frequencies of 1616 cmꢀ1 for 1 (1614 cmꢀ1 for 2) indicating
coordination of the imine nitrogen to Cu(II). For 1, the
assigned to the strong band at 1531 cmꢀ1 whereas the
attributed to the 1450 cmꢀ1 band (for 2: as(COOꢀ) = 1535 cmꢀ1
m
as(COOꢀ) is
s(COO-) is
m
m
,

Y.-j. Yan et al. / Inorganica Chimica Acta 413 (2014) 84–89
87
Fig. 1. Molecular structure of the complex 1. Displacement ellipsoids are drawn at the 30% probability level. Hydrogen atoms are omitted for clarity.
Fig. 2. (a) Hydrogen-bonded 2D framework of 1, (yellow dash line refer to H-bond; (b) Simplified hydrogen-bonded (4,4) net of 1, green nodes refer to binuclear molecule
unit, yellow sticks refer to H-bond; (c) Hydrogen-bonded wave-like structure of 1 along b axis. (For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
Fig. 4. Structure of complex 2 showing the hydrogen bonding dimeric unit (yellow
dashed line refers to hydrogen bond). (For interpretation of the references to colour
in this figure legend, the reader is referred to the web version of this article.)
Fig. 3. Molecular structure of the complex 2. Displacement ellipsoids are drawn at
the 30% probability level.
p
–
p⁄ transitions of benzene ring are observed at ꢃ211 nm for
the ligand H2L1 (208 nm for H2L2) and ꢃ216 nm for 1 (212 nm
for 2). There is a peak for both the ligands and for the complexes
at approximately 200 nm, which may be attributed to the n ? p⁄
transition of the phenols. The peaks at approximately 370 nm in
the spectra of the ligand H2L1 (315 nm for H2L2) and 374 nm in that
of 1 (362 nm for 2) are assigned to the imine n–p⁄ transitions. The
m
s(COOꢀ) = 1450 cmꢀ1). An absorption band at 636 cmꢀ1 for 1
(671 cmꢀ1 for 2) may be assigned for
m(Cu–N). The band in the re-
gion 1156 cmꢀ1 for 1 (1148 cmꢀ1 for 2) may be assigned for
m(C-
O) stretching [26].

88
Y.-j. Yan et al. / Inorganica Chimica Acta 413 (2014) 84–89
weak asymmetric broad band at 600 nm observed for 1 and
650 nm, observed for 2, is assigned to a d–d transition.
10ꢀ4) indicating a very weak coupling. This weak magnetic ex-
change can be understood considering the large Cu–Cu distance
(11.22 Å) [28].
For 2, the value of
v
MT is 0.881 cm3 molꢀ1K at 300 K, which is
also close to the value of 0.87 cm3 molꢀ1K expected for two
magnetically independent Cu(II) (S = 1/2) centers. It decreases
slowly from room temperature to 10 K (0.788 cm3 molꢀ1 K) and
then decreases rapidly at a low temperature reaching a value of
0.506 cm3 molꢀ1 K at 2 K. Analysis of the experimental magnetic
3.5. Magnetic properties
The magnetic susceptibility of the polycrystalline sample of 1
and 2 were examined within 2–300 K. The results are shown in
Figs. 5 and 6 with
the
MT value of the presented complex is 0.856 cm3 molꢀ1K. This
value correspond to two isolated copper(II) ions with one unpaired
electron with g = 2.13. With decreasing temperature, the MT value
vM and vMT versus T plots. At room temperature,
v
data was also performed by using Eq. (1). Least-square fitting leads
P
to g = 2.11(1), J = ꢀ0.47(2) cmꢀ1 (R = [(
v
MT)obs ꢀ (
v
MT)calc]2/
P
[(
v
MT)obs]2 = 9.0 ꢂ 10ꢀ4). The negative value of J indicates the
v
remains almost constant until ca. 25 K and then it decreases shar-
existence of weak antiferromagnetic coupling interactions in 2.
ply, giving the minimum value of 0.529 cm3 molꢀ1 K at 2 K. The
drop in
vMT at low-temperatures indicates the presence of a very
4. Conclusions
weak antiferromagnetic coupling between the copper(II) ions.
Analysis of the experimental magnetic data was performed by
using the Bleaney–Bowers expression,[27] based on the following
isotropic Hamiltonian: H = ꢀJ(S1 S2):
In conclusion, copper complex with Schiff base ligands contain-
ing b-amino acid: [Cu2L2(bipy)2(EtOH)2] 1 and [CuL2(imi)] 2 were
prepared. In the crystal structure of 1, each Cu(II) ion is five-coor-
dinated with tridentate chelating Schiff base ligand, ethanol mole-
cule and the 4,40-bipyridine, which linked two adjacent metal
centers to form the binuclear complex. The binuclear unit are
further linked by hydrogen bond to construct a 2D wave-like
supramolecular architecture. In complex 2, Cu(II) ion is four-coor-
dinated with a square-planar geometry. The imidazole-carboxyl
hydrogen bond linked the two CuL2(imi) units together. The vari-
able temperature magnetic susceptibility measurements of 1 and
2 revealed that weak antiferromagnetic coupling interaction exist.
.
Ng2b2 2 expðJ=kTÞ
vMT ¼
:
ð1Þ
k
1 þ 3 expðJ=kTÞ
The parameters N, b and k in Eq. (1) have their usual meanings,
J = Singlet–triplet splitting. Least-square fitting of experimental
data leads to the following parameter J = ꢀ3.14(5) cmꢀ1 and
P
P
g = 2.13(1) for 1 (R = [(
vMT)obs ꢀ (
v
MT)calc]2/ [(
v
MT)obs]2 = 1.7 ꢂ
0
50
100
150
200
250
300
0.9
0.8
0.7
0.6
0.5
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Acknowledgments
This work was financial support by the National Natural Science
Foundation of China (No. 20901067), Qianjiang Talent Project (No.
2011R10076), Natural Science Foundation of Zhejiang Province,
China (No. Y4080342, LY13B010004), and SRF for ROCS, SEM.
Appendix A. Supplementary material
CCDC 876705 and 936230 contains the supplementary crystal-
lographic data for 1 and 2. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2014.01.007.
0
50
100
150
200
250
300
T / K
Fig. 5. Temperature dependence of
vMT (s) and vM (h) for 1. The solid line
corresponds to the best fit according to the parameters in Eq. (1) given in the text.
References
[1] (a) S. Khatua, J. Kang, J.O. Huh, C.S. Hong, D.G. Churchill, Cryst. Growth Des. 10
(2010) 327;
0
50
100
150
200
250
300
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
(b) L.H. Abdel-Rahman, R.M. El-Khatib, L.A.E. Nassr, A.M. Abu-Dief, J. Mol.
Struct. 1040 (2013) 9;
(c) Z.Z. Li, L. Du, J. Zhou, M.R. Zhu, F.H. Qian, J. Liu, P. Chen, Q.H. Zhao, Dalton
Trans. 41 (2012) 14397;
(d) Y.N. Belokon, V.I. Maleev, D.A. Kataev, T.F. Saveleva, T.V. Skrupskaya, Y.V.
Nelyubina, M. North, Tetrahedron Asymmetry 20 (2009) 1746;
(e) Y.N. Belokon, V.I. Maleev, D.A. Kataev, I.L. Mal’fanov, A.G. Bulychev, M.A.
Moskalenko, T.y.F. Saveleva, T.y.V. Skrupskaya, K.A. Lyssenko, I.A. Godovikov,
M. North, Tetrahedron Asymmetry 19 (2008) 822;
0.30
0.25
0.20
0.15
0.10
0.05
0.00
(f) J. Müller, G. Kehr, R. Fröhlich, G. Erker, Eur. J. Inorg. Chem. (2005) 2836.
[2] (a) C.T. Chen, Y.H. Lin, T.S. Kuo, J. Am. Chem. Soc. 130 (2008) 12842;
(b) M. Gharagozlou, D.M. Boghaei, Spectrochim. Acta, Part A: Mol. Biomol.
Spectrosc. 71 (2008) 1617;
(c) M. Ebel, D. Rehder, Inorg. Chem. 45 (2006) 7083;
(d) J.M. Rivera, H. Reyes, A. Cortés, R. Santillan, P.G. Lacroix, C. Lepetit, K.
Nakatani, N. Farfán, Chem. Mater. 18 (2006) 1174;
0
50
100
150
200
250
300
(e) P.A.N. Reddy, M. Nethaji, A.R. Chakravarty, Eur. J. Inorg. Chem. (2004) 1440.
[3] (a) G. Desiraju, Acc. Chem. Res. 24 (1991) 290;
T / K
(b) K.A. Siddiqui, G.K. Mehrotra, J. Mrozinski, R.J. Butcher, J Mol. Struct. 964
(2010) 18;
Fig. 6. Temperature dependence of
vMT (s) and vM (h) for 2. The solid line
corresponds to the best fit according to the parameters in Eq. (1) given in the text.
(c) T. Fujimura, H. Seino, M. Hidai, Y. Mizobe, J. Organomet. Chem. 689 (2004)

Y.-j. Yan et al. / Inorganica Chimica Acta 413 (2014) 84–89
89
738;
[14] J.F. Cutfield, D. Hall, T.N. Waters, Chem. Commun. (1967) 785.
[15] J.E. Davies, Acta Crystallogr., Sect. C 40 (1984) 903.
[16] X. Zhang, C. Du, D. Chen, M. Huang, Chin. J. Inorg. Chem. 26 (2010) 489.
[17] N. Kobakhidze, N. Farfán, M. Romero, J.M. Méndez-Stivalet, M.G. Ballinas-
López, H. García-Ortega, O. Domínguez, R. Santillan, F. Sánchez-Bartéz, I.
Gracia-Mora, J. Organomet. Chem. 695 (2010) 1189.
[18] A.R. Minter, A.A. Fuller, A.K. Mapp, J. Am. Chem. Soc. 125 (2003) 6846.
[19] (a) J. Dong, L. Li, G. Liu, T. Xu, D. Wang, J. Mol. Struct. 986 (2011) 57;
(b) M.Z. Wang, Z.X. Meng, B.L. Liu, G.L. Cai, C.L. Zhang, X.Y. Wang, Inorg. Chem.
Commun. 8 (2005) 368;
(d) J.K. Bera, T.T. Vo, R.A. Walton, K.R. Dunbar, Polyhedron 22 (2003) 3009.
[4] (a) A. García-Raso, J.J. Fiol, A. López-Zafra, A. Tasada, I. Mata, E. Espinosa, E.
Molins, Polyhedron 25 (2006) 2295;
(b) A. García-Raso, J.J. Fiol, F. Bádenas, M. Quirós, Polyhedron 15 (1996) 4407.
[5] (a) S. Khatua, K. Kim, J. Kang, J.O. Huh, C.S. Hong, D.G. Churchill, Eur. J. Inorg.
Chem. (2009) 3266;
(b) B. Lou, F. Jiang, D. Yuan, B. Wu, M. Hong, Eur. J. Inorg. Chem. (2005) 3214;
(c) S. Warda, P. Dahlke, S. Wocaldo, W. Massa, C. Friebel, Inorg. Chim. Acta 268
(1998) 117;
(d) S.A. Warda, Acta Crystallogr., Sect. C 53 (1997) 697.
[6] (a) H.D. Bian, X.E. Yang, Q. Yu, Z.L. Chen, H. Liang, S.P. Yan, D.Z. Liao, J. Mol.
Struct. 872 (2008) 40;
(c) P.A.N. Reddy, M. Nethaji, A.R. Chakravarty, Inorg. Chim. Acta 337 (2002)
450;
(d) G. Plesch, C. Friebel, S.A. Warda, Transition Met. Chem. 22 (1997) 433.
[20] G.L. Qiu, Y.J. Li, W. Yang, Y. Zou, J. Chem. Crystallogr. 41 (2011) 898.
[21] (a) G.M. Sheldrick, SADABS, University of Göttingen:Göttingen, Germany, 1996.;
(b) SIR97 program, A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C.
Giacovazzo, A. Guagliardi, A.G.G. Moliterni, G. Polidori, R. Spagna, J. Appl. Cryst.
32 (1999) 115.
[22] SHELXTL program G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[23] (a) G. Marin, V. Kravtsov, Y.A. Simonov, V. Tudor, J. Lipkowski, M. Andruh, J.
Mol. Struct. 796 (2006) 123;
(b) S.P. Xu, L. Shi, Y. Pei, Y. Yang, G. Xu, H.L. Zhu, J. Coord. Chem. 63 (2010)
3463;
(c) J. Sivy, V. Kettmann, J. Krätsmar-Smogrovic, O. Svajlenova, C. Friebel, G.
Plesch, Z. Anorg. Allg. Chem. 583 (1990) 55.
[7] (a) H. Bian, F. Huang, X. Yang, Q. Yu, H. Liang, J. Coord. Chem. 61 (2008) 802;
(b) Y.Z. Yuan, J. Zhou, D.Q. Li, X. Liu, Z.F. Chen, K.B. Yu, Acta Crystallogr., Sect. E:
Struct. Rep. Online 61 (2005) m1444.
[8] S.Y. New, Y. Thio, L.L. Koh, T.S. Andy Hor, F. Xue, CrystEngComm 13 (2011)
2114.
[9] S.P.S. Rao, H. Manohar, R. Bau, J. Chem. Soc., Dalton Trans. (1985) 2051.
[10] T. Ueki, T. Ashida, Y. Sasada, M. Kakudo, Acta Crystallogr. 22 (1967) 870.
[11] I. Bkouche-Waksmam, J.M. Barbe, A. Kvick, Acta Crystallogr., Sect. B 44 (1988)
595.
[12] T. Ueki, T. Ashida, Y. Sasada, M. Kakudo, Acta Crystallogr., Sect. B 25 (1969)
328.
(b) J. Geng, T. Tao, K.H. Gu, G. Wang, W. Huang, Inorg. Chem. Commun. 14
(2011) 1978;
(c) Z.H. Weng, Z.L. Chen, F.P. Liang, J. Coord. Chem. 62 (2009) 1801.
[24] T. Ueki, T. Ashida, V. Sasada, K. Kakudo, Acta Crystallogr., Sect. B 25 (1969) 328.
[25] W.J. Zhou, Y.Z. Jiang, Y. Zou, Acta Crystallogr., Sect. E 66 (2010) m579.
[26] N. Mondal, D.K. Dey, S. Mitra, K.M. Abdul Malik, Polyhedron 19 (2000) 2707.
[27] B. Bleaney, K.D. Bowers, Proc. R. Soc. London A 214 (1952) 451.
[28] P.S. Mukherjee, S. Dalai, G. Mostafa, T.H. Lu, E. Rentschlerc, N.R. Chaudhuri,
New J. Chem. 25 (2001) 1203.
[13] D.M. Boghaei, M. Gharagozlou, Spectrochim. Acta, Part A: Mol. Biomol.
Spectrosc. 67 (2007) 944.