Synthesis, structural characterization, thermal and electrochemical studies of the N,N′-bis[(3,4-dichlorophenyl)methylidene]cyclohexane-1,4-diamine and its Cu(II), Co(II) and Ni(II) metal complexes

Article abstract of DOI:10.1016/j.saa.2008.06.012

In this study, N,N′-bis[(3,4-dichlorophenyl)methylidene]cyclohexane-1,4-diamine (L) and its Cu(II), Co(II) and Ni(II) complexes were prepared and characterized by the analytical and spectroscopic methods. The analytical data show the composition of the me

Full text of DOI:10.1016/j.saa.2008.06.012

Spectrochimica Acta Part A 71 (2009) 1648–1654
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, structural characterization, thermal and electrochemical studies
of the N,Nꢀ-bis[(3,4-dichlorophenyl)methylidene]cyclohexane-1,4-diamine
and its Cu(II), Co(II) and Ni(II) metal complexes
Mustafa Dolaza, Vickie McKeeb, Ays¸ egül Gölcüa, Mehmet Tümera,∗
a K.Maras¸ Sütc¸ ü Imam University, Chemistry Department, Faculty of Science and Arts, k.maras s. i. uni., 46100 K.Maras¸, Turkey
b University of Loughborough, Department of Chemistry, Loughborough LE11 3TU, United Kingdom
a r t i c l e i n f o
a b s t r a c t
In this study, N,Nꢀ-bis[(3,4-dichlorophenyl)methylidene]cyclohexane-1,4-diamine (L) and its Cu(II), Co(II)
and Ni(II) complexes were prepared and characterized by the analytical and spectroscopic methods. The
analytical data show the composition of the metal complex to be [M2L(Cl)4(H2O)2], where L is the Schiff
base ligand. The conductance data indicate that all the complexes are non-electrolytes. The compound (L)
behaves as a monodentate ligand. But, obtained complexes have binuclear nature. The electrochemical
properties of the metal complexes are dependent on reversible, irreversible and quasi-reversible redox
waves in the anodic and cathodic regions due to oxidation and reduction of the metal ions. The single
crystal of the ligand (L) was obtained from CH3CN solution. Space group and crystal system of the ligand
are P21/C and monoclinic, respectively.
Article history:
Received 12 March 2008
Received in revised form 9 May 2008
Accepted 10 June 2008
Keywords:
X-ray
Schiff base
Electrochemical
Reversible
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
it had been believed that the formation of these complexes would
be obstructed by the steric constraint due to the bulky i-Pr group.
Schiff bases are typically formed by the condensation of a
primary amine and an aldehyde. The resultant functional group,
R1HC N–R2, is called an imine and is particularly for binding metal
ions via the N atom lone pair, especially when used in combina-
tion with one or more donor atoms to form polydentate chelating
ligands or macrocycles. Schiff bases are used as substrates in the
preparation of a number of industrial and biologically active com-
pounds via ring closure, cycloaddition, and replacement reactions
[1]. Metal complexes with Schiff bases as ligands have played an
important part in the development of coordination chemistry as
a whole. However, it was not until the 1950s that concrete and
rapid advances in this field became evident. In the early days
the main efforts were directed toward synthesis and characteriza-
tion of rather fundamental complexes, which do not look striking
nowadays but were strongly needed in those days. Some of typ-
ical examples included metal complexes of the following types:
M(II)(X-Sal-NR)2, M(III)(X-Sal-NR)3, and so on, where X-Sal-NR
(formula II) denotes bidentate Schiff bases [2]. To cite another
example, it was regarded as significant to synthesize complexes of
the formula Co(X-Sal-NR)3, R = i-Pr, where X = 5-Br and 5-NO2 [3];
Moreover, Schiff bases are also known to have biological activ-
ities such as antimicrobial [4–7], antifungal [8–10], antitumor
[11–13], and herbicides [14]. Schiff bases have also been employed
as ligands for complexation of metal ions [15]. On the indus-
trial scale, they have wide range of applications such as dyes
and pigments [16]. In the earlier articles [17,18], we reported
the synthesis and the ligating properties of the Schiff base lig-
ands derived from condensation of salicylaldehyde, o-vanillin and
(
)trans-1,2-cyclohexanediamine, with Ni(II) and Cu(II) metal ions
with different kinds of bridging ligands; we found that the Schiff
base behaves either as a tetradentate (N2O2) ligand, depending
upon the nature of the anions present and the reaction conditions.
In this study, we prepared the racemic Schiff base ligand (L) and
its copper(II), cobalt(II) and nickel(II) metal complexes. Molecular
structure of the Schiff base ligand (L) was investigated by X-ray
technique. Moreover, the spectroscopic, analytical and thermal
properties of the compounds were studied. The electrochemical
properties of the ligand and complexes were investigated in differ-
ent solvents media at 50, 75, 100 and 250 mV s−1 scan rates.
2. Experimental
2.1. General
∗
Corresponding author. Tel.: +90 344 219 10 93; fax: +90 344 219 10 42.
E-mail addresses: mtumer@ksu.edu.tr, mehmettumer22@hotmail.com
The metal salts CuCl2·2H2O, CoCl2·6H2O and NiCl2·6H2O
(M. Tümer).
and organic solvents were purchased from commercial
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.06.012

M. Dolaz et al. / Spectrochimica Acta Part A 71 (2009) 1648–1654
1649
sources and used as received, unless noted otherwise. 3,4-
Dichlorobenzaldehyde, )trans-1,4-cyclohexanediamine and
lowed by the addition of the Schiff base (0.428 g, 1 mmol) in ethanol
and reaction mixture stirred upon heating for 24 h. The obtained
precipitates were filtered, washed with methanol and dried in air.
Results of analytical and spectroscopic results of the copper(II),
cobalt(II) and nickel(II) complexes are given as below:
(
([CH3(CH2)3]4NBF4) were obtained from Fluka. Elemental analyses
(C, H, N) were performed using a LECO CHNS 932 elemental anal-
yser. IR spectra were obtained using KBr discs (4000–400 cm−1
)
on a Shimadzu 8300 FT-IR spectrophotometer. The electronic
spectra in the 200–900 nm range were obtained on a Perkin Elmer
Lambda 45 spectrophotometer. Magnetic measurements were
carried out by the Gouy method using Hg[Co(SCN)4] as calibrant.
Molar conductances of the Schiff base ligands and their transition
metal complexes were determined in DMF (∼10−3 M) at room
temperature using a Jenway Model 4070 conductivity meter. Mass
spectra of the ligands were recorded on a LC/MS APCI AGILENT
1100 MSD spectrophotometer. 1H and 13C NMR spectra were
recorded on a Varian XL-200 instrument. TMS was used as internal
standard and d6-DMSO solvent. The metal and chloride contents
of the complexes were determined as gravimetrically according
to the known procedure [19]. The thermal analyses studies of
the complexes were performed on a Perkin Elmer Pyris Diamond
DTA/TG Thermal System under nitrogen atmosphere at a heating
rate of 10 ◦C/min.
Cyclic voltammograms were recorded on a Iviumstat Electro-
chemical workstation equipped with a low current module (BAS
PA-1) recorder. The electrochemical cell was equipped with a BAS
glassy carbon working electrode (area 4.6 mm2), a platinum coil
auxiliary electrode and a Ag/Ag+ (0.03 M AgNO3) reference elec-
trode filled with tetrabutylammonium tetrafluoroborat (NBu4BF4)
(0.1 M) in DMSO and DMF solvents and adjusted to 0.00 V vs SCE.
Cyclic voltammetric measurements were made at room tempera-
ture in an undivided cell (BAS model C-3 cell stand) with a platinum
counter electrode and an Ag/Ag+ (0.03 M AgNO3) reference elec-
trode (BAS). All potentials are reported with respect to Ag/Ag+
(0.03 M AgNO3). The solutions were deoxygenated by passing dry
nitrogen through the solution for 30 min prior to the experiments,
and during the experiments the flow was maintained over the
solution. Digital simulations were performed using DigiSim 3.0 for
windows (BAS, Inc.). Experimental cyclic voltammograms used for
the fitting process had the background subtracted and were cor-
rected electronically for ohmic drop.
[Cu2L(Cl)4(H2O)2]: (C20H22Cl8Cu2N2O2). Yield: 70%, color: light
green, m.p.: >250 ◦C. Elemental analyses, found (calcd. %): C, 32.81
(32.77); H, 3.06 (3.02); N, 3.85 (3.82); Cu, 17.40 (17.34); Cl, 38.74
(38.69). Mass spectrum (LC/MS APCI): m/z 733 [M]+ (45%), m/z
697 [M − 36] (20%). UV–vis: (ꢀmax, nm; εmax, M−1 cm−1, DMF
as solvent): 627 (190), 338 (3128), 301 (1233), 288 (5414), 273
(3.2 × 10−4). FT-IR: (KBr, cm−1): 3448 ꢁ(H2O), 2916, 2831 ꢁ(CH2),
1606 ꢁ(CH N), 441 ꢁ(M–N). ꢂ(1 × 10−3 M): 4.2 ꢃ−1 cm2 mol−1
ꢄeff B.M. (298 K): 1.85 (for per metal ion).
.
[Co2L(Cl)4(H2O)2]: (C20H22Cl8Co2N2O2). Yield: 66%, color: blue,
m.p.: >250 ◦C. Elemental analyses, found (calcd. %): C, 33.21 (33.18);
H, 3.10 (3.06); N, 3.91 (3.87); Co, 16.34 (16.28); Cl, 39.23 (39.18).
Mass spectrum (LC/MS APCI): m/z 724 [M]+ (38%), m/z 688 [M − 36]
(20%). UV–vis: (ꢀmax, nm; εmax, M−1 cm−1, DMF as solvent): 670
(135), 342 (2466), 305 (1283), 295 (5401), 271 (4.4 × 10−4). FT-IR:
(KBr, cm−1): 3450 ꢁ(H2O), 2956, 2918 ꢁ(CH2), 1605 ꢁ(CH N), 440
ꢁ(M–N). ꢂ(1 × 10−3 M): 3.8 ꢃ−1 cm2 mol−1. ꢄeff B.M. (298 K): 4.25
(for per metal ion).
[Ni2L(Cl)4(H2O)2]: (C20H22Cl8Ni2N2O2). Yield: 69%, color:
green, m.p.: >250 ◦C. Elemental analyses, found (calcd. %): C, 33.25
(33.21); H, 3.11 (3.07); N, 3.90 (3.87); Ni, 16.27 (16.23); Cl, 39.27
(39.21). Mass spectrum (LC/MS APCI): m/z 724 [M]+ (44%), m/z 688
[M − 36] (25%). 1H NMR: (d6-DMSO as solvent, ı in ppm): 8.25
(s, CH N, 2H), 6.38–7.15 (m, Ar–H, 6H), 3.22–1.20 (m, CH/CH2,
10H). 13C NMR: (d6-DMSO as solvent, ı in ppm): 164.21 (CH N),
115.04–152.15 (Ar–C), 50.13–26.76 (CH/CH2). UV–vis: (ꢀmax, nm;
εmax, M−1 cm−1, DMF as solvent): 597 (176), 302 (1104), 295
(5208), 278 (2935), 275 (7.6 × 10−4). FT-IR: (KBr, cm−1): 3421
ꢁ(H2O), 2918 ꢁ(CH2), 1606 ꢁ(CH N), 462 ꢁ(M–N). ꢂ(1 × 10−3 M):
5.1 ꢃ−1 cm2 mol−1. ꢄeff B.M. (298 K): diamagnetic.
2.4. X-ray structure solution and refinement for the Schiff base
ligand L
X-ray crystal diffraction analyses of the ligand L from crystals
were grown by crystallization from acetonitrile solution for a long
time. The data were collected at 150(2) K on a Bruker APEX II diffrac-
tometer. The structure was solved using direct methods and refined
on F2 using all the reflections [20]. All the non-hydrogen atoms
were refined using anisotropic atomic displacement parameters,
and hydrogen atoms were inserted at calculated positions using
a riding model. Parameters for data collection and refinement are
summarized in Table 1.
2.2. Preparation of the ligand (L)
3,4-Dichlorobenzaldehyde (2 mmol, 350 mg) in ethanol (20 mL,
anhydrous) and
( )trans-1,4-cyclohexanediamine (1 mmol,
114 mg) in ethanol (20 mL) were mixed and refluxed for about 4 h
at 85 ◦C. The color of the solution changed to light yellow. After
cooling the solution, the resulting precipitate was filtered and
washed with cold ethanol. Crystals of the ligand (L) were obtained
by recrystallization from CH3CN solution.
L: (C20H18 Cl4N2). Yield: 90%, color: bright white, m.p.: 92 ◦C. Ele-
mental analyses, found (calcd. %): C, 56.13 (56.10); H, 4.27 (4.24); N,
6.58 (6.54). 1H NMR: (d6-DMSO as solvent, ı in ppm): 8.29 (s, CH N,
2H), 7.27–7.87 (m, Ar–H, 6H), 3.32–1.66 (m, CH/CH2, 10H). 13C NMR:
(d6-DMSO as solvent, ı in ppm): 158.76 (CH N), 138.42–129.22
(Ar–C), 71.00–34.34 (CH/CH2). Mass spectrum (LC/MS APCI): m/z
427 [M − 1]+ (80%), m/z 428 [M]+ (100%), m/z 430 [M + 2]2+ (25%).
UV–vis: (ꢀmax, nm; εmax, M−1 cm−1, DMF as solvent): 327 (1988),
306 (2332), 288 (1.4 × 10−3). FT-IR: (KBr, cm−1): 2934, 2895 ꢁ(CH2),
3. Results and discussion
The analytical and physical data of the Schiff base ligand and its
complexes are given in Section 2. The analytical data show that the
metal to ligand ratio is 2:1 in all the complexes. The composition of
the complexes is [M2L(Cl)4(H2O)], where M Co(II), Ni(II) and Cu(II)
and
L = N,Nꢀ-bis[(3,4-dichlorophenyl)methylidene]cyclohexane-
1,4-diamine. The ligand (L) is soluble in common polar organic
solvents such as EtOH, MeOH, CHCl3 and CH2Cl2. The complexes
are soluble in DMF and DMSO, but insoluble in EtOH, MeOH,
CHCl3 and CH2Cl2 organic solvents. The compounds are very stable
solids at room temperature without decomposition. The ligand L
was obtained as colorless thin plate crystals with 90% yield. This
yield was higher than the yields of the complexes. The low molar
conductance values (Section 2) of 10−3 M solutions in DMF showed
1639 ꢁ(CH N). ꢂ(1 × 10−3 M): 1.4 ꢃ−1 cm2 mol−1
.
2.3. Preparation of complexes
Copper(II), cobalt(II) and nickel(II) complexes were obtained
according to a general procedure: CuCl2·2H2O (0.241 g, 2 mmol)
was dissolved in ethanol and stirred under reflux for 30 min, fol-

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M. Dolaz et al. / Spectrochimica Acta Part A 71 (2009) 1648–1654
Table 1
tively. The mass spectra of the complexes show the molecular ion
and corresponding fragmentation peaks.
Crystal data and structure refinement for the Schiff base ligand (L)
The infrared spectral data of all compounds were given in Sec-
tion 2. In the spectrum of the ligand, the ꢁ(CH N) vibration of the
azomethine group is shown at the 1639 cm−1. In the complexes,
this vibration shifted to the lower regions and can be attributed
to the complexation of the metal ion and nitrogen atoms of the
azomethine groups. In the spectra of the complexes, the vibrations
ꢁ(H2O) of the coordinated water molecules are seen in the range
3450–3421 cm−1. The bands in the range 440–462 cm−1 are ꢁ(M–N)
vibration.
The electronic spectra of the ligand and their complexes were
recorded in DMF as a solvent. The spectral data are given in Sec-
tion 2. In the spectra of the ligand, the band at the 327 nm may
be assigned to the n–␲* transitions. The observed bands in the
range 306–288 nm can be attributed to the ␲–␲* and ␲–␦* transi-
tions. The complexes exhibit multiple absorptions in the UV–visible
region. In the visible region, the copper(II), cobalt(II) and nickel(II)
complexes show the d–d transitions at 627, 670 and 597 nm, respec-
tively. Moreover, the bands at 342 and 338 nm can be assigned
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C20H18 Cl4N2
428.16
150 (2) K
0.71073 Å
Monoclinic
P2(1)/C
a = 15.0953(11) Å, ˛ = 90◦
b = 6.2513(5) Å, ˇ = 92.286(1)◦
c = 10.4304(8) Å, ꢅ = 90◦
983.48(13) Å3
Unit cell dimensions
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
2
1.446 mg/m3
0.609 mm−1
440
Crystal size
0.35 × 0.19 × 0.05 mm3
Colorless thin plate
2.70–27.50◦
Crystal description
Theta range for data collection
Index ranges
−19 ≤ h ≤ 19, −8 ≤ k ≤ 8, −13 ≤ l ≤ 13
Reflections collected
Independent reflections
Completeness to theta = 27.50◦
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2 sigma(I)]
R indices (all data)
Largest diff. peak and hole
CCDC deposition number
9197
2256 [R (int) = 0.0292]
100.0%
Semi-empirical from equivalents
0.9702 and 0.8152
Full-matrix least-squares on F2
2256/0/118
to the d (M) → ␲*(ligand) metal to ligand charge transfer tran-
␲
sitions. The intra-ligand transitions n–␲*, ␲–␲* and ␦–␲* in the
metal(II) complexes are seen in the range 271–305 nm. The bands
with higher energy in the UV region are of intra-ligand ␲–␲* type
or charge-transfer transitions involving energy levels which are
higher in energy than the ligand lowest unoccupied molecular
orbital (LUMO).
1.026
R1 = 0.0320, wR2 = 0.0844
R1 = 0.0397, wR2 = 0.0901
0.329 and −0.271 Å−3
680833
The magnetic moment measurements were carried out at room
temperature and obtained values are given in Section 2. The
nickel(II) complex has diamagnetic character, and therefore, the
nickel(II) ion has square-planar geometry around the metal ion. The
magnetic moment of Co(II) complex is 4.25 ꢄB. Thus, in agreement
with the electronic spectral studies, Co(II) complex has tetrahedral
geometry. The electronic spectral results clearly indicated square-
planar geometry for the Cu(II) system, which should contain one
unpaired electron, where ꢄeff value would be at 1.85 ꢄB.
them to be non-electrolytes [21]. From the acetonitrile solution,
we obtained suitable single crystals for X-ray diffraction analysis.
The 1H and 13C NMR spectra of the ligand and its nickel(II) com-
plex were recorded using d6-DMSO as a solvent, and the spectral
data are given in Section 2. The 1H and 13C NMR spectra of the ligand
were given in Fig. 1. The ligand has a symmetric nature. Therefore,
the hydrogen atoms in the two benzene rings are equivalent, as
they are the two halves of the cyclohexane rings. For example, two
hydrogen atoms of the azomethine groups have one signal in the 1H
NMR spectrum. The azomethine groups were shown at ı = 8.29 ppm
as a singlet. In the nickel(II) complex, these groups shifted to the
lower regions and this shift shows that the nitrogen atom of the
CH N group coordinated to the nickel ion. Aromatic rings pro-
tons are shown in the range ı = 7.27–7.87 ppm as a multiplet. In
the 1H NMR spectrum of the complex, the aromatic ring protons
shifted to the lower regions. In the ligand, the hydrogen atoms of the
CH2/CH groups in the cyclohexane ring are observed in the range
ı = 3.32–1.66 ppm, but, in the complex, this signals shifted to the
lower or higher regions.
In order to get further information about the ligand and its Ni(II)
complex, the 13C NMR spectra were investigated. In the ligand, the
azomethine carbon atom is shown at ı 166.20 ppm. In the nickel(II)
complex, this signal shifted to the lower region. This situation con-
firms that the nitrogen atom of the CH N group coordinated to
the nickel(II) ion. The aromatic ring C atoms were shown in the
range ı = 117.40–114.15 ppm. The C atoms of the cyclohexane ring
were shown in the range ı = 27.50–53.18 ppm. In the spectrum of
the complex, the signals of the aromatic and aliphatic carbon atoms
shifted to the lower regions.
3.1. Experimental molecular geometry of the ligand (L)
The structure of the Schiff base ligand (L) has been solved by
X-ray diffraction. X-ray crystal diffraction analyses of the ligand
L from crystals were grown by crystallization from acetonitrile
solution for a long time. The data were collected at 150(2) K on
a Bruker APEX II diffractometer. The structure was solved using
direct methods and refined on F2 using all the reflections [20].
All the non-hydrogen atoms were refined using anisotropic atomic
displacement parameters and hydrogen atoms were inserted at
calculated positions using a riding model. Parameters for data
collection and refinement are summarized in Table 1. N,Nꢀ-bis[(3,4-
dichlorophenyl)methylidene]cyclohexane-1,4-diamine crystallises
in P21/C, the molecule lies on a centre of symmetry, in an extended
conformation. A thermal ellipsoid diagram [22,23] of the molecule
indicating atom numbering scheme with thermal ellipsoids at 50%
probability is illustrated in Fig. 2 and the crystal packing in the unit
cell is shown in Fig. 3. There are no very striking intermolecular
␲–␲ or H–␲ interactions. There are no solvent molecules in the
crystal structure.
The mass spectral studies for the ligand and its metal complexes
were done and obtained data are given in Section 2. The mass spec-
tra for the ligand and its metal complexes were characterized by a
peak corresponding to Schiff base fragmentation. The mass spec-
trum of the ligand (L) shows molecular ion peak ([M]+, 100%) at
m/z 428. Moreover, the fragmentation peaks at m/z 427 (80%) and
430 (25%) can be attributed to the [M − 1] and [M + 2] ions, respec-
The space group is P21/C with a = 15.0953(11) Å, b = 6.2513(5) Å,
c = 10.4304(8) Å, ˛ = 90(3), ˇ = 92.286(1)◦, ꢅ = 90◦. According to the
single crystal X-ray study, the colorless thin plate form consists of a
molecule with a dihedral angle of 117.93◦ [C(7)–N(1)–C(8)]. Atomic
coordinates (× 104) and equivalent isotropic displacement param-
eters (× 103 Å2) for the Schiff base ligand (L) are given in Table 2.
Selected bond lengths and bond angles are listed in Table 3.

M. Dolaz et al. / Spectrochimica Acta Part A 71 (2009) 1648–1654
1651
Fig. 1. (a and b) 1H and 13 C NMR spectra of the ligand L.
Six-membered cyclohexane ring of the symmetric Schiff base
ligand has an ideal chair conformation, with puckering param-
eters [24]. Q = 0.577(4)◦, Â = 177.2(3)◦ and ϕ = 88.1(7)◦ and all the
geometric parameters in the ring are quite normal. Each phenyl
moiety in the molecule is planar. There are also deviations from
the overall planarity of the phenyl ring C1, C2, C3, C4, C5, C6 but
this time describing an envelope. The deviations from the main
plane through C2, C3, C4 and C5 do not exceed 0.42 Å. All bond
Fig. 2. The molecular structure of the title compound L, showing 50% probability displacement ellipsoids and the atom numbering scheme.

1652
M. Dolaz et al. / Spectrochimica Acta Part A 71 (2009) 1648–1654
Fig. 3. The crystal packing arrangement for the ligand L. The symbols a, b and c are
unit cell dimensions.
Table 2
Atomic coordinates (×104) and equivalent isotropic displacement parameters
(× 103 Å2) for the Schiff base ligand (L)
x
y
z
U (eq)
C(1)
C(2)
C(3)
Cl(1)
C(4)
Cl(2)
C(5)
C(6)
C(7)
N(1)
C(8)
C(9)
C(10)
2296(1)
2676(1)
2201(1)
2714(1)
1330(1)
737(1)
6404(2)
4557(2)
3249(2)
1030(1)
3766(3)
2176(1)
5567(3)
6886(3)
7879(2)
7549(2)
9163(2)
8103(2)
10273(3)
2003(1)
2526(1)
3315(1)
4004(1)
3577(2)
4608(1)
3040(2)
2258(2)
1242(1)
1092(1)
399(1)
25(1)
24(1)
26(1)
35(1)
32(1)
49(1)
39(1)
34(1)
25(1)
23(1)
22(1)
28(1)
27(1)
938(1)
1421(1)
2828(1)
3643(1)
4139(1)
4639(1)
4784(1)
−669(1)
1345(1)
U (eq) is defined as one third of the trace of the orthogonalized Uij tensor.
Table 3
Bond lengths (Å) and angles (◦) for the Schiff base ligand (L)
C(1)–C(6)
C(1)–C(2)
1.391(2)
1.391(2)
C(1)–C(7)
1.476(2)
C(2)–C(3)
1.382(2)
C(3)–C(4)
1.392(2)
C(3)–Cl(1)
C(4)–C(5)
1.7310(16)
1.380(3)
C(4)–Cl(2)
C(5)–C(6)
1.7383(16)
1.387(2)
C(7)–N(1)
1.262(2)
N(1)–C(8)
C(8)–C(10)
1.4642(17)
1.525(2)
C(8)–C(9)
1.523(2)
C(9)–C(10)#1
C(10)–C(9)#1
C(6)–C(1)–C(2)
C(6)–C(1)–C(7)
C(2)–C(1)–C(7)
C(3)–C(2)–C(1)
C(2)–C(3)–C(4)
C(2)–C(3)–Cl(1)
C(4)–C(3)–Cl(1)
C(5)–C(4)–C(3)
C(5)–C(4)–Cl(2)
C(3)–C(4)–Cl(2)
C(4)–C(5)–C(6)
C(1)–C(6)–C(5)
N(1)–C(7)–C(1)
C(7)–N(1)–C(8)
N(1)–C(8)–C(10)
N(1)–C(8)–C(9)
C(10)–C(8)–C(9)
C(8)–C(9)–C(10)#1
C(8)–C(10)–C(9)#1
1.528(2)
1.528(2)
119.02(14)
120.63(14)
120.28(14)
120.61(14)
119.77(15)
119.16(12)
121.04(12)
120.19(14)
119.66(13)
120.14(13)
119.81(16)
120.58(16)
121.25(14)
117.93(12)
108.69(11)
109.85(12)
110.41(12)
110.89(12)
111.43(12)
Symmetry transformations used to generate equivalent atoms: (#1) −x + 1, −y + 2,
−z.

M. Dolaz et al. / Spectrochimica Acta Part A 71 (2009) 1648–1654
1653
Fig. 4. Cyclic voltammogram of the ligand (L) in the presence of 0.1 M NBu4BF4 in
DMF (sr: 250 mV s−1).
lengths and angles in the phenyl rings have normal values. The
new structure shows considerable flexibility. Exact conformation,
as a balance between packing and molecular bonding forces, is
complicated by charge transfer interactions which is also a bal-
ance between electronic and steric effects. As the cyclohexyl ring
has tetrahedral geometry around the C atoms, ␲-electron delo-
calization does not continue all over the molecule. This property
becomes only between the phenyl rings and azomethine groups.
Two molecules were found in the unit cell which differed in their
conformations.
Thermal behaviour of the complexes was characterized using
DTA and TGA/DTG techniques. The DTA/TG measurements were
carried out in the range 10–1100 ◦C. Thermal decompositions of the
complexes were occurred at three steps. In the first step, the com-
plexes loss the coordinated water molecules in the temperature
range 100–200 ◦C. Loss of water molecules at such high tempera-
tures indicates that the H2O molecules are coordinated to the metal
ions. This is in agreement with the C, H and N analyses. In the second
step, coordinated chloride ions walk away from the complexes in
the temperature range 225–300 ◦C. In the third step, organic parts
of the complexes decomposed to metal oxides. The factors affect-
ing the thermal stability of transition metal complexes in the solid
state are not well understood. In addition, intermolecular factors
may operate and control the stability of the complexes. Thermal
stability order of the complexes are Ni(II) > Co(II) > Cu(II).
Fig. 5. Reduction–oxidation processes of the ligand in DMF solution.
in DMF solution (E1/2 = 290 mV, with Ipc:Ipa = 1.0, assignable to a
CuII–CuI process). In Fig. 6, while the processes I and II show the
oxidation peaks, processes III and IV indicate the reduction process.
In DMSO and 75 mV s−1 scan rate, there is similar process as at scan
rate 50 mV s−1. The [Co2L(Cl)4(H2O)2] and [Ni2L(Cl)4(H2O)2] com-
∼
plexes are quasi-reversible at Epc/Epa: −0.36/0.51 V (Ipc:Ipa 0.70)
=
∼
and Epc/Epa: 0.42/0.54 V (Ipc:Ipa 0.77), respectively. Although the
=
forward peaks in reduction process in DMF solution and reverse
peaks in oxidation process in DMSO solution are almost invari-
ant, the position and broadness of the return peak varies markedly
depending on theanion present. This suggests that close association
of the anions with the metal(II) centres may occur following reduc-
tion at the electrode surface. No MI–M0 (M: Cu(II), Co(II) and Ni(II))
reduction was detected for the metal complexes. Of all of the com-
plexes were sufficiently soluble in DMF and DMSO to allow a cyclic
Cyclic voltammograms of the ligand and complexes were run
in DMF–0.1 M NBu4BF4 and DMSO–0.1 M NBu4BF4 as supporting
electrolyte at room temperature. Unless otherwise stated, all poten-
tials quoted refer to measurements run at a scan rates of 50, 75,
100 and 250 mV s−1 and against an internal ferrocene–ferrocenium
standard. The results of these experiments are summarized in
Table 4. The electrochemical curve of the ligand (L) at 250 mV s−1
is shown in Fig. 4. The CV curves of the ligand at the dif-
ferent scan rates in DMF solution show the reversible process
∼
(Ipc:Ipa 1.0). Its potential range changes from −1.31 to −1.19 V
=
(Epc) and 1.15 to 1.39 V (Epa). This process is shown in Fig. 5. As
seen from Fig. 4, the reduction–oxidation process of the ligand
(L) is reversible. In DMSO solution and at 50 mV s−1 scan rate, the
∼
ligand behaves the reversible character (Ipc:Ipa 1.0). The electro-
=
chemical curves of the [Cu2L(Cl)4(H2O)2] and [Co2L(Cl)4(H2O)2]
complexes are shown in Figs. 6 and 7. In addition to the above
ligand-based processes, the [Cu2L(Cl)4(H2O)2], [Co2L(Cl)4(H2O)2]
and [Ni2L(Cl)4(H2O)2] complexes show a reversible, irreversible
and quasi-reversible two-electron reduction, respectively. The cop-
per(II) complex has a reversible process at 50 mV s−l scan rate
Fig. 6. Cyclic voltammogram of the [Cu2L(Cl)4(H2O)2] complex in the presence of
0.1 M NBu4BF4 in DMF (sr: 100 mV s−1).

1654
M. Dolaz et al. / Spectrochimica Acta Part A 71 (2009) 1648–1654
1EZ, UK (fax: +44 1223 336 033; e-mail: deposit@ccdc.cam.ac.uk or
URL: http://www.ccdc.cam.ac.uk).
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Fig. 7. Cyclic voltammogram of the [Co2L(Cl)4(H2O)2] complex in the presence of
0.1 M NBu4BF4 in DMF (sr: 50 mV s−1).
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Supplementary material
Full crystallographic data for the reported ligand (L) has been
deposited with the Cambridge Crystallographic Data Center, CCDC
No. 680833. Copies of this information may be obtained by writing
your request to: The Director, CCDC, 12 Union Road, Cambridge CB2
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