Two dinuclear NiII–CdII complexes of reduced ONNO-type Schiff bases: Synthesis, crystal structures, thermal kinetic analysis and DFT studies

Article abstract of DOI:10.1007/s10973-017-6720-7

Two ONNO-type Schiff bases, bis-N,N′-(salicylidene)-1,3-diaminopropane and bis-N,N′-(2-hydroxyacetophenylidene)-1,3-propanediamine, were reduced using NaBH₄ and converted to two phenol–amine-type tetradentate ligands, bis-N,N′-(2-hydroxybenzyl)-1,3-diaminopropane (L^HH₂) and bis-N,N′-[1(2-hydroxyphenyl)ethyl]-1,3-diaminopropane (LAC^HH₂). These ligands were used to prepare two Ni^II–Cd^II heterodinuclear complexes, namely [DMF·NiL^H·CdI₂·DMF] and [DMF·NiLAC^H·CdBr₂·DMF] in DMF medium. The molecular structure and unit cells of these complexes have been elucidated by the use of X-ray diffraction data. The thermogravimetric analysis of the compounds revealed that as the temperature is increased, the first coordinative DMF molecule was removed from the structure followed by a second coordinative DMF molecule with the complete decomposition of the complex. The activation energies and Arrhenius pre-exponential factor of these thermal reactions were determined by the use of isothermal Coats–Redfern, nonisothermal Ozawa–Flynn–Wall and Kissinger–Akahira–Sunose methods. The results obtained for the first thermal reaction were similar since the structure of both complexes remained intact during this process. Also, the theoretical calculations of the bond lengths, bond angles and natural bond orbital analysis of both complexes were carried out using the algorithms embedded in Gaussian 09 software.

Full text of DOI:10.1007/s10973-017-6720-7

J Therm Anal Calorim
DOI 10.1007/s10973-017-6720-7
Two dinuclear NiII–CdII complexes of reduced ONNO-type Schiff
bases
Synthesis, crystal structures, thermal kinetic analysis and DFT studies
1
M. Sonmez H. Nazir1 E. Emir1 I. Svoboda2 L. Aksu3 O. Atakol1
•
•
•
•
•
¨
Received: 28 February 2017 / Accepted: 18 September 2017
´
´
Ó Akademiai Kiado, Budapest, Hungary 2017
Abstract Two ONNO-type Schiff bases, bis-N,N0-(sali-
cylidene)-1,3-diaminopropane and bis-N,N0-(2-hydroxy-
acetophenylidene)-1,3-propanediamine, were reduced using
NaBH4 and converted to two phenol–amine-type tetradentate
ligands, bis-N,N0-(2-hydroxybenzyl)-1,3-diaminopropane (LHH2)
both complexes were carried out using the algorithms
embedded in Gaussian 09 software.
Keywords Heteronuclear complexes Á Crystal structure Á
Thermal kinetic analysis Á DFT
and
bis-N,N0-[1(2-hydroxyphenyl)ethyl]-1,3-diamino-
propane (LACHH2). These ligands were used to prepare two
NiII–CdII heterodinuclear complexes, namely [DMFÁNiLH-
CdI2ÁDMF] and [DMFÁNiLACHÁCdBr2ÁDMF] in DMF
medium. The molecular structure and unit cells of these
complexes have been elucidated by the use of X-ray
diffraction data. The thermogravimetric analysis of the
compounds revealed that as the temperature is increased, the
first coordinative DMF molecule was removed from the
structure followed by a second coordinative DMF molecule
with the complete decomposition of the complex. The
activation energies and Arrhenius pre-exponential factor of
these thermal reactions were determined by the use of
isothermal Coats–Redfern, nonisothermal Ozawa–Flynn–
Wall and Kissinger–Akahira–Sunose methods. The results
obtained for the first thermal reaction were similar since the
structure of both complexes remained intact during this
process. Also, the theoretical calculations of the bond
lengths, bond angles and natural bond orbital analysis of
Introduction
Bis-N,N0-(salicylidene)-1,3-diaminopropane (LH2) is an
ONNO-type Schiff base which includes two azomethine
groups in its structure first used by P. Pfeifer in coordina-
tion chemistry about 90 years ago [1, 2]. It is a very pop-
ular ligand in coordination chemistry literature due to its
tendency to give polynuclear complexes. It was observed to
give dinuclear complexes in 1976 and trinuclear complexes
in 1990 [3, 4]. From that date on, there have been vast
number of studies reported related to polynuclear com-
plexes prepared with this ligands in the literature. There are
dinuclear [5–13] and trinuclear [14–20] complexes pre-
pared by the use of LH2 or its derivatives reported in the
recent literature. Azomethine groups are easily reduced
with NaBH4 in amphyprotic solvents by the conversion of
the imine bond to secondary amine [21, 22]. In this study,
LH2 was synthesized with 2-hydroxybenzaldehyde and 1,3-
propanediamine; LACH2 was synthesized with 2-hydrox-
yacetophenone and 1,3-diaminopropane. These Schiff
bases were the reduced to amine compounds in MeOH with
NaBH4 (Fig. 1).
& H. Nazir
nazir@science.ankara.edu.tr
1
The phenol–amine-type ligands obtained by the reduc-
tion in ONNO-type Schiff bases form very interesting
coordination compounds. These ligands have a strong
tendency to give polynuclear complexes [6, 22]. This study
is related to the characterization of two heterodinuclear
NiII–CdII complexes synthesized by the use of these ligands
Department of Chemistry, Science Faculty, Ankara
University, Tandogan, 06100 Ankara, Turkey
2
Strukturforschung, FB Materialwissenschaft, TU-Darmstadt,
Petersenstrasse 23, 64287 Darmstadt, Germany
3
Department of Chemistry Education, Faculty of Education,
Gazi University, Teknikokullar, 06500 Ankara, Turkey
123

¨
M. Sonmez et al.
R
R
R
R
NaBH4
in MeOH
C
N
N
C
N
C
C
N
H
H
H
H
HO
OH
HO
OH
Phenol - amine
R = H
LHH2
Phenol -imine
R = H LH2
R = CH3 LACHH2
R = CH3 LACH2
Fig. 1 The formula of the Schiff bases and reduced Schiff bases
S
R
R
C
NH HN
Ni
C
R = H , S = DMF , X = I, [NiLH·CdI2·(DMF)2] (LHH2)
H
H
R = CH3, S = DMF, X = Br, [NiLACH·CdBr2·(DMF)2] (LACHH2)
O
O
Cd
S
X
X
Fig. 2 The structures of the complexes prepared
(Fig. 2). The ligands were characterized by element anal-
ysis, FTIR, MS and 1H-NMR–13C-NMR methods. The
structure of the complexes was identified by X-ray
diffraction. The thermogravimetric analysis revealed that
the complexes follow different decomposition patterns.
Isothermal and nonisothermal–isoconversional thermoki-
netic analyses were used in order to bring cogent expla-
nation to these differences.
three reflectional ATR units used for with 4 cm-1 accu-
racy. The C, H and N analyses were performed on
Eurovector 3018 C, H, N, S analyzer. Metal analyses were
recorded on GBC Avanta PM Model atomic absorption
spectrometer using FAAS mode. Complex (2–3 mg) was
dissolved in 1 mL HNO3(63%):H2O2(%30) (v/v, 50–50%)
with heating, diluted to 100 mL and fed to nebulizer of
atomic absorption spectroscopy for metal analysis. Halo-
gen analyses were carried out gravimetrically using AgNO3
in aqueous media. Approximately 100–150 mg complex
was dissolved in 5 mL HNO3 (63%) by heating and diluted
to 100 mL in a graduated flask. To this, solution was added
excess of 0.1 M AgNO3 solutions. The precipitated silver
halide was filtered from a G3 glass crucible and dried in an
oven at 80 °C and weighed for the halogen analysis. The
mass spectra of the ligands were obtained by Shimadzu,
2010 plus with direct inlet (DI) unit with an electron
impact ionizer. DI temperature was varied between 40
and 140 °C, and ionization was carried out with electrons
with 70 eV energy. The NMR spectra of the ligands were
recorded with a Varian brand Mercury model 400 MHz
NMR spectrophotometer in d6-DMSO solution. The
thermogravimetric analyses were performed by Shimadzu
DTG 60H. The thermogravimetric analyses were per-
formed between a temperature range of 30–600 °C at
heating rates of 5, 10, 15, 20 and 25 °C min-1 under N2
atmosphere in Pt pans. The instrument was calibrated
with metallic In and Zn.
Also theoretical calculations were carried out by using
Gaussian 09W (revision D.01) software [32]. The calcu-
lations were performed by DFT/B3LYP/LanL2DZ method
in a gas phase. The outer shell d electron densities and
relative energy levels of Ni(II) and Cd(II) ions of the
coordination compound were determined by the use of
natural bond orbital (NBO) method installed in Gaussian
09. The difference between these coordination compounds
was evaluated by the use of these values and the data
reported in the literature.
Experimental
Materials and apparatus
All the chemicals used in the experimental procedure were
purchased from Merck Company, and they were used
without further purification. The IR spectra were taken by
the Shimadzu Infinity FTIR Spectrometer equipped with
123

Two dinuclear NiII–CdII complexes of reduced ONNO-type Schiff bases
ꢂ
ꢀ
ꢁꢃ
X-ray diffraction study
gðaÞ
AR
2RT
Ea
ln
¼ ln
1 À
À
T2
bEa
Ea
RT
A single crystals of [NiLHÁCdI2Á(DMF)2] and [NiLACH-
CdBr2Á(DMF)2] were analyzed on an Oxford Diffraction
Xcalibur single-crystal X-ray diffractometer with a sap-
Here the term b is the rate of heating in °C min-1, Ea is
the activation energy in kJ mol-1, A is Arrhenius pre-ex-
ponential factor in min-1, R is gas constant in J mol-1 K-1
and t is a constant, T is the absolute temperature in Kelvin,
g(a) is the completed fraction of the reaction which is
determined from h graphs, m1 and m2 are initial and final
masses and mT is the mass remained at the temperature of
the T Kelvins. The value of g(a) of is simply given by
g(a) = (m1-mT)/(m1-m2). Ea and A values were calcu-
lated from slopes and interceptions of the straight lines
obtained in the plots of graphically calculated values of
lnb, ln(b/T2) and ln(g(a)/T2) against 1/T.
phire
CCD
detector
using
MoKa
radiation
˚
(k = 0.71073 A) operating in x/2h scan mode. The unit
cell dimensions were determined and refined by using the
angular settings of 25 automatically centered reflections in
1.977° B h B 26.37° range for [NiLHÁCdI2Á(DMF)2] and
4.09°–26.37° for [NiLACHÁCdBr2Á(DMF)2]. The data of
[NiLHÁCdI2Á(DMF)2] were collected at 301(2) K, and for
other complex, they were collected at 293(2) K. The
empirical absorption corrections were applied by the
semiempirical method via the CrysAlis CCD software [33].
The model was obtained from the results of the cell
refinement, and the data reductions were carried out using
the solution software SHELXL97 [34]. The structure of the
complex V was solved by direct methods using the
SHELXS-97 software implemented in the WinGX package
[35]. Supplementary material for structure has been
deposited with the Cambridge Crystallographic Data Cen-
ter as CCDC no: 1520351 [NiLHÁCdI2Á(DMF)2] and
Preparation of the ligands
The first step is the synthesis of the relevant Schiff bases
(LH2 and LACH2) by the reaction of 1,3-propanediamine
and related aldehydes. The ligands were then prepared
simply by the reduction in these Schiff bases.
Preparation of N,N0-bis(2-hydroxyphenylidene)-1,3-
propanediamine (LH2)
606868
[NiLACHÁCdBr2Á(DMF)2]
(deposit@ccdc.-
cam.ac.uk or http://www.ccdc.cam.ac.uk).
The related Schiff base was prepared via condensation
reaction in EtOH under hydrothermal conditions using
2-hydroxybenzaldehyde and 1,3-diaminepropane. 2-Hy-
droxybenzaldehyde (0.1 mol, 12.20 g) was dissolved in
120 mL warm EtOH; then, 0.05 mol (3.70 g) of 1, 3-di-
aminepropane was added to this solution and heated up to
the boiling point. After cooling, yellow crystals were fil-
tered and dried in air. Yield: 90–95%, mp: 58 °C deter-
mined by TG. Elemental Analysis, C17H18N2O2: Expected
% C: 72.32, H: 6.43, N: 9.92; Found % C: 71.95, H: 6.33,
Thermal calculations
Thermal dissociation activation energies (Ea) and Arrhe-
nius pre-exponential factors (A) of the coordination com-
pounds were determined and compared with each other by
the use of isothermal Coats–Redfern (CR) and non-
isothermal Ozawa–Flayn–Wall (OFW) and Kissinger–
Akahira–Sunose (KAS) methods [23–31]. The formula
used in the Ozawa–Flynn–Wall (OFW) calculation was as
follows [24]:
N: 10.09. IR data (cm-1): mO–H
3021–3019, mC–H(Aliph): 2929–2862, mC=N: 1629, mC=C(ring)
:
2627, mC–H(Ar)
:
:
0:0048AEa
RgðaÞ
Ea
ln b ¼ ln
À 1:0516
RT
1608, mC–O(Phenol): 1274–1151, dC–H(Ar): 762. 1HNMR data
in d6-DMSO (d, ppm): 13.51 (s) (O–H), 8.60 (s) (–CH=),
7.43 (d) (HAr), 7.32(t) (HAr), 6.88 (t) (HAr), 3.68 (t) (N–
CH2–), 2.01 (p) (–CH2–). 13CNMR data in d6-DMSO (d,
ppm): 166.6, 161.1, 132.7, 132.1, 119.1, 118.9 (CAr),
116.9 (–C=N), 58.5 (N–CH2–), 31.9 (–CH2–). MS (m/z):
282 [M]?, 161 [HO–C6H4–CH=N–CH2–CH2–CH2]?, 148
[HO–C6H4–CH=N–CH2–CH2]? (base peak), 134 [HO–
C6H4–CH=N–CH2]?, 120 [HO–C6H4–CH=N]?, 107 [HO–
C6H4–CH2]?, 77 [C6H5]?.
Kissinger–Akahira–Sunose equation stated below,
which was developed approximately at same time with
OFW method, has been frequently used in kinetic analysis
today, [25–27].
b
AEa
Ea
ln ¼ ln
T2
À
RgðaÞ RT
As known, the international Confederation of Thermal
Analysis and Calorimetric councel (ICTAC) is recom-
mending the use of nonisothermal studies. However,
isothermal Coats–Redfern (CR) method has also been used
in this study due to its similarity with the nonisothermal
methods. The formula used in the CR calculations is given
below [30, 31].
123

¨
M. Sonmez et al.
Preparation of N,N-bis (2-hydroxybenzyl)-1,3-
propanediamine (LHH2)
Preparation of N,N0-bis(2-
hydroxyacetophenylidene)-1,3-propanediamine
(LACH2)
3.0 g of bis-N,N0-(salicylidene)-1,3-propanediamine (LH2)
was dissolved in 70.0 mL of MeOH by rigorous stirring.
The resulting solution was heated up to 50 °C adding solid
NaBH4 in small portions under strong mixing conditions
until the solution became colorless [30, 31]. The solution
was stirred for 10 min before adding 300 mL of ice water
to it. The final mixture was left on the bench for 24 h. The
white precipitate was filtered off and dried in air. The
product was recrystallized from hot EtOH: H2O (2:1, v/v).
Yield: 55–60%, mp: 107 °C. Elemental Analysis,
C17H22N2O2: Expected % C: 71.30, H: 7.74, N: 8.01;
This Schiff base was prepared via condensation reaction in
EtOH under hydrothermal conditions using 2-hydroxy-
acetophenone and 1,3-diaminopropane. 2-Hydroxyace-
tophenone (0.1 mol, 13.60 g) was dissolved in 150 mL of
warm EtOH; then, 0.05 mol (3.70 g) of 1,3-diamino-
propane was added to it and the resulting solution was
heated up to the boiling point. After cooling, yellow
crystals were filtered off and dried in air. Yield: 92%, mp:
123.6 °C (determined by TG). Elemental Analysis,
C19H22N2O2: Expected % C: 73.52, H:7.14, N: 9.02; Found
% C: 73.09, H: 6.35, N: 8.82 Important IR data (cm-1):
Found % C: 70.86, H: 6.69, N: 8.37. IR (cm-1): mO–H
:
:
:
2627, mN–H
2967–2823,
:
3307, mC–H(Ar)
:
3055–3023, mC–H(Aliph)
mC–O(Phenol)
m
m
C–H(Ar): 3059–3017, mC–H(Aliph): 2944–2843, mC=N: 1612,
C=C(ring): 1571, mC–O(Phenol): 1232–1159, dC–H(Ar): 754.
mC=C(ring) 1606–1595,
:
1253–1099, dC–H(Ar): 752. 1H-NMR data in d6-CH3SOCH3
(d, ppm): 13.22 (s) (O–H), 7.12 (m) (HAr), 6.67 (m) (HAr),
4.73(broad) (N–H), 3.80 (m) (N–CH2–), 2.56 (m) (N–CH–
), 1.15 (m) (–CH2–). 13CNMR data in d6-DMSO (d, ppm):
145.41, 128.56, 127.92, 126.86, 124.85, 116.28, 65.43,
61.17, 18.62. MS (m/z): 286 (molcular peak), 179 [HO–
C6H4–CH2–NH–CH2–CH2–CH2–NH]?, 163 [HO–C6H4–
CH2–NH–CH2–CH2–CH2]?, 150 [HO–C6H4–CH2–NH–
CH2–CH2]?, 134 [HO–C6H4–CH2–NH–CH2]?, 122 [HO–
C6H4–CH2–NH]?, 107 [HO–C6H4–CH2]? (base peak), 90
[C6H4–CH2]?, 77 [C6H5]?.
1HNMR data in d6-DMSO (d, ppm): 7.06–6.97 (m) (HAr), -
6.72–6.63 (t, d) (t, d) (HAr), 3.82 (q) (N–CH2–), 2.42–2.34
(M) (N–CH–), 1.62 (p) (–CH2–), 1.29–1.27 (d). 13C-NMR
data in d6-DMSO (d, ppm): 157.11, 127.72, 127.52,
118.42, 115.74, 57.26, 45.01, 29.02, 22.05. MS (m/z): 310
(molcular peak), 174 [O–C6H4–CCH3=NH–CH2–CH2]?,
162 [HO–C6H4–CCH3=NH2–CH2]?, 148 [HO–C6H4–
CCH3=NH2]? (base peak), 136 [HO–C6H4–CCH3=NH2]?,
107 [HO–C6H4–CH2]?, 91 [C6H4–CH2]?.
Preparation of bis-N,N0-[1-(2-hydroxyphenyl)ethyl]-
1,3-propanediamine (LACHH2)
3.0 g
of
bis-N,N0-(2-hydroxyacetophenylidene)-1,3-
propanediamine (LACH2) was dissolved in 100.0 mL of
(a)
(b)
C10
C13
C8
C9
C9
C25
C5
C11
O2
C7
N2
N1
C14
C10
C12
C8
C15
C6
C23
C17
C4
O4
C20
Ni1
C16
N2
N1
O4
O3
C18
C19
C1
N3
C3
C21
O3
Ni1
C7
C21
N4
C22
C19
O1
N3
C24
C2
C22
O1
C20
N4
C6
C13
C12
O2
Cd1
C23
C17
C1
C4
C5
C2
Cd1
C16
Br2
Br1
C14
I1
C15
C3
I2
Fig. 3 The pictorial illustrations of [NiLHÁCdI2Á(DMF)2] (a) and [NiLACHÁCdBr2Á(DMF)2] (b) complexes drawn by Pluton program
123

Two dinuclear NiII–CdII complexes of reduced ONNO-type Schiff bases
N: 8.54. IR (cm-1): mO–H: 2643, mN–H: 3309, mC–H(Ar)
3041–3007, mC–H(Aliph): 2968–2850, mC=C(ring): 1608–1587,
C–O(Phenol): 1253–1109, dC–H(Ar): 758. 1HNMR data in d6-
:
Table 1 Crystal data and data collection values
(NiLHÁCdI2Á(DMF)2) (NiLACHÁCdBr2Á(DMF)2)
m
Formula weight/ 855.45
g mol-1
789.52
CH3SOCH3 (d, ppm): 7.12–6.85 (m) (HAr), 6.67–6.34 (t, d)
(HAr), 4, 73(broad) (N–H), 3.80 (q) (–N–CH2–), 2.56
(m) (N–CH–), 2.43 (m) (CH–CH3), 1.32 (d) (–CH2–).
13CNMR data in d6-DMSO, ppm): 157.12, 127.90, 127.74,
127.54, 118.44, 115.77, 57.29, 57.12, 29.05, 22.07. MS (m/
z): 314 (MP), 193 [O–C6H4–CHCH3–NH–CH2–CH2–
CH2–NH]?, 179 [O–C6H4–CH2–NH–CH2–CH2–CH2–
NH]?, 164 [O–C6H4–CH2–NH–CH2–CH2–CH2]?, 150
T/K
301 (2)
Blue
293 (2)
Blue
Crystal color
Crystal system
Space group
Orthorhombic
Pbca
Orthorhombic
Pbca
˚
a/A
20.230 (5)
14.607 (1)
20.648 (4)
90.00
20.249 (2)
14.881 (2)
20.565 (1)
90.00
˚
b/A
[O–C6H4–CH2–NH–CH2–CH2]?,
136
[HO–C6H4–
˚
c/A
CCH3=NH2]?, 121 (base peak) [HO–C6H4–CH–NH]?, 91
[HO–C6H4–CH2]?.
a
b
c
90.00
90.00
90.00
90.00
3
˚
V/A
6101 (2)
8
6196.8 (11)
8
Preparation of the complexes
Z
Calc. density/
g cm-3
l/mm-1
1.863
1.693
The coordination compounds in this study were synthe-
sized at a single step by the use of the template method as
its analogs in the literature by the reaction of stoichiometric
amount of NiCl2 and CdX2 (X = Br or I) salts in DMF
medium.
3.370
3.908
F (000)
3312
3152
Radiation
wavelength/A
0.71073
0.71073
˚
Preparation of [NiLHÁCdI2Á(DMF)2]
H range/°
Index ranges
1.97–26.37
4.09–26.37
- 24 \ h \ 24
- 12 \ k \ 18
- 25 \ l \ 24
0.8284, 0.6313
41,369/6195
- 25 \ h \ 25
- 9 \ k \ 18
- 25 \ l \ 25
0.6513, 0.2454
42,590/6273
0.002 mol (0.565 g)of LHH2 was dissolved in 60 mL hot
DMF by constant stirring, and the solution was heated up to
100–110 °C before the addition of 0.002 mol (0.476 g)
NiCl2.6H2O in 20 mL MeOH and 1.0 mL Et3N and finally
0.002 mol CdI2 (0.732 g) in 20 mL hot MeOH. The final
mixture was rigorously stirred and left on the bench for
5–14 days. The resulting blue crystals were filtered off,
washed with MeOH and finally dried in air. Elemental
Analysis, C23H34N4O4NiCdI2: Expected % C: 32.21, H:
3.99, N: 6.58, Ni: 6.84, Cd: 13.11, I: 29.85; Found % C:
31.43, H: 3.78, N: 6.38 Ni: 6.52, Cd: 12.45, I: 30.47. IR
Tmax, Tmin
Reflections
collected
Reflections
unique
6195
6273
´
R1, wR2 (2o)
R1, wR2 (all)
Data/parameters
GOOF of F2
0.0667–0.2213
0.1364–0.2388
6195/320
0.0499–0.1391
0,1105–0.1644
6273/340
0.992
1.015
Largest
difference peak
2.147, - 2.340
0.740, - 0.655
(cm-1): mN–H: 3241, mC–H(Ar): 3039–3019, mC–H(Aliph)
2945–2861, mC=O(DMF) 1644, mC=C(ring) 1595–1573,
C–H(Aliph): 1472, mC–O(Phenol): 1308–1127, dC–H(Ar): 756.
:
-3
˚
:
:
hole/e A
d
CCDC No.
1,520,351
606,868
Preparation of [NiLACHÁCdBr2Á(DMF)2]
0.002 mol (0.630 g) LACHH2 was dissolved in 60 mL hot
DMF under stirring and heated approximately to
100–110 °C. Then, a solution of 0.002 mol (0.476 g)
NiCl2.6H2O in 20 mL MeOH and 1.0 mL Et3N and finally
a solution of 0.002 mol CdBr2.4H2O (0.690 g) in 30 mL
hot MeOH were added to it. The resulting brown mixture
was rigorously stirred and left on the bench for 3–4 weeks.
The resulting blue crystals were filtered off, washed with
MeOH and finally dried in air. Elemental Analysis, C25-
H34N4O4NiCdBr2: Expected % C: 38.03, H: 4.85, N: 7.09,
Ni: 7.43, Cd: 14.23, Br: 20.24; Found % C: 37.29, H: 4.44,
MeOH by rigorous stirring. The resulting solution was
heated up to 50 °C adding solid NaBH4 in small portions
under strong mixing conditions until the solution became
colorless [30, 31]. The solution was stirred for 10 min
before adding 500 mL of ice water to it. The final mixture
was left on the bench for 24 h. The white crystals were
filtered off and dried in air. The product bis-N,N-[1-(2-
hydroxphenyl)ethyl]-1,3-propanediamine (LACHH2) was
recrystallized from hot EtOH. Yield: 50–55%, mp:
123–124 °C. Elemental Analysis, C19H26N2O2: Expected
% C: 72.58, H: 8.33, N: 8.90; Found % C: 72.41, H: 6.97,
123

¨
M. Sonmez et al.
Table 2 The selected bond lengths and angles of around coordination sphere of the complexes prepared
˚
Bond lengths/A
Complex
Bond angles/°
(NiLHÁCdI2Á(DMF)2)
N(1)–Ni(1)
N(1)–H(1A)
N(2)–Ni(1)
N(2)–H(2A)
O(1)–Ni(1)
O(1)–Cd(1)
O(2)–Ni(1)
O(2)–Cd(1)
O(3)–Ni(1)
O(4)–Ni(1)
Br(1)–Cd(1)
Br(2)–Cd(1)
2.101 (6)
0.85 (7)
O(2)–Ni(1)–O(1)
O(2)–Ni(1)–N(2)
O(1)–Ni(1)–N(2)
O(2)–Ni(1)–O(4)
O(1)–Ni(1)–O(4)
N(2)–Ni(1)–O(4)
O(2)–Ni(1)–N(1)
O(1)–Ni(1)–N(1)
N(2)–Ni(1)–N(1)
O(4)–Ni(1)–N(1)
O(2)–Ni(1)–O(3)
O(1)–Ni(1)–O(3)
N(2)–Ni(1)–O(3)
O(4)–Ni(1)–O(3)
N(1)–Ni(1)–O(3)
O(1)–Cd(1)–O(2)
O(1)–Cd(1)–Br(1)
O(2)–Cd(1)–Br(1)
O(1)–Cd(1)–Br(2)
O(2)–Cd(1)–Br(2)
Br(1)–Cd(1)–Br(2)
N(2)–Ni(1)–O(4)
N(2)–Ni(1)–N(1)
O(4)–Ni(1)–N(1)
N(2)–Ni(1)–O(1)
O(4)–Ni(1)–O(1)
N(1)–Ni(1)–O(1)
N(2)–Ni(1)–O(3)
O(4)–Ni(1)–O(3)
N(1)–Ni(1)–O(3)
O(1)–Ni(1)–O(3)
N(2)–Ni(1)–O(2)
O(4)–Ni(1)–O(2)
N(1)–Ni(1)–O(2)
O(1)–Ni(1)–O(2)
O(3)–Ni(1)–O(2)
O(1)–Cd(1)–O(2)
O(1)–Cd(1)–I(2)
O(2)–Cd(1)–I(2)
O(1)–Cd(1)–I(1)
O(2)–Cd(1)–I(1)
I(2)–Cd(1)–I(1)
83.10 (16)
90.97 (18)
172.68 (18)
91.95 (16)
94.14 (16)
90.33 (18)
172.5 (2)
89.5 (2)
2.084 (5)
0.83 (7)
2.070 (4)
2.215 (4)
2.067 (4)
2.227 (4)
2.119 (4)
2.087 (4)
2.5257 (10)
2.5409 (10)
96.4 (2)
89.71 (17)
93.45 (16)
87.19 (16)
88.90 (18)
174.56 (17)
85.02 (18)
76.30 (14)
121.16 (10)
120.02 (11)
109.21 (10)
108.55 (10)
115.36 (4)
90.3 (3)
(NiLACHÁCdBr2Á(DMF)2)
N(1)–Ni(1)
N(1)–H(1A)
N(2)–Ni(1)
N(2)–H(2A)
O(1)–Ni(1)
O(1)–Cd(1)
O(2)–Ni(1)
O(2)–Cd(1)
O(3)–Ni(1)
O(4)–Ni(1)
I(1)–Cd(1)
I(2)–Cd(1)
2.092 (9)
0.9100
96.4 (3)
2.078 (8)
0.9100
85.4 (3)
172.3 (3)
87.3 (3)
2.093 (6)
2.238 (7)
2.112 (7)
2.239 (7)
2.100 (7)
2.087 (7)
2.7527 (14)
2.7447 (15)
90.7 (3)
89.8 (3)
174.0 (3)
88.6 (3)
93.3 (3)
91.0 (3)
93.6 (3)
172.6 (3)
81.9 (3)
92.4 (3)
76.0 (2)
121.72 (17)
122.04 (19)
105.19 (17)
109.47 (18)
115.64 (4)
123

Two dinuclear NiII–CdII complexes of reduced ONNO-type Schiff bases
(a)
(b)
100
120
100
80
60
40
20
0
80
60
40
20
0
0
100 200 300 400 500 600 700
Temperature/°C
0
100
200
300
400
500
600
Temperature/°C
Fig. 4 a TG b DTA curves of the complexes. Black: [NiLHÁCdI2Á(DMF)2], red: [NiLACHÁCdBr2Á(DMF)2]
Fig. 5 Detailed curves of
(a) TG (b) DTA curves
(a)
(b)
40
20
0
100
80
60
100
200
300
100
200
300
Temperature/°C
Temperature/°C
N:6.89, Ni: 7.36, Cd: 14.07, I: 21.46. IR (cm-1): mN–H
3246, C–H(Ar):3061–3008, mC–H(Aliph) 2980–2862,
:
calculations made with Parts program reveal the fact that
the distance between Ni(II) ions and the approximate plane
m
:
H-
˚
formed by O1N1N2O2 atoms is 0.0197 (4) A in [NiL
m
m
C=O(DMF): 1647, mC=C(ring): 1593–1568, dC–H(Aliph): 1481,
C–O(Phenol): 1263–1113, dC–H(Ar): 759–740.
H-
˚
CdI2Á(DMF)2] complex and 0.0346(13) A in [NiLAC
CdBr2Á(DMF)2], [36, 37]. The chelate ring formed by
NiN1C8C9C10N2 atoms is in chair conformation in both
complexes. Parst calculation revealed that the angle
between N1C8C10N2 plane and C8C9C10 in the chelate
ring is 62.22 (0.24)° in [NiLHÁCdI2Á(DMF)2] complex and
61.57 (0.96)° in [NiLACHÁCdBr2Á(DMF)2] complex. The
angles between N1NiN2 and N1C8C10N2 planes in the
chelate ring were found to be 29.49 (0.08)° in [NiLH-
CdI2Á(DMF)2] and 28.16 (0.04)° in [NiLACHÁCdBr2-
(DMF)2] complex. Both complex structures are very
similar to each other. Cd(II) ion is in a distorted tetrahedral
sphere. As shown in Table 2, the angles of Br1CdBr2 and
I1CdI2 are approximately 115° and the angle of O1CdO2
in both complexes is around 76°. This value is very far
away from the angle of tetrahedron. The TG and DTA
curves of the compound are given in Fig. 4a, b.
Results and discussion
The pictorial representation drawn with the Pluton software
of the complexes, [NiLHÁCdI2Á(DMF)2] and [NiLACH-
CdBr2Á(DMF)2], is illustrated in Fig. 3a and b, the data
collection methods and the intrinsic features of the crystals
are listed in Table 1, and the related bond lengths and
angles calculated from the coordination spheres are tabu-
lated in Table 2.
As in the similar complexes reported in the literature,
Ni(II) ions in both complexes were placed in an octahedral
coordination sphere. On the other hand, Cd(II) ions are
located in a distorted tetrahedral coordination sphere
[5–7, 10]. It is high probable that the plane formed by
O1N1N2O2 donor atoms in both complexes is the equa-
torial plane of the octahedron because coordination bond
between the Ni(II) and DMF oxygens is longer than the one
formed between Ni(II) and phenolic oxygens. The
Although these two complexes have similar structures,
their TG curves are significantly different. For TG curves
of these complexes, the first expectation and observations
are separation of the coordinative DMF molecules from the
123

¨
M. Sonmez et al.
Table 3 The thermoanalytical data of the complexes
Complex
1 Thermal reaction
1 mol DMF removal
2 Thermal reaction second DMF removal and decomposition
Temperature
range/°C
Expected/found Temperature range/°C
mass loss/%
Expected mass loss (for the
second mass loss of DMF
molecule)/found mass loss/
% (for second mass loss of
DMF molecule)–
decomposition mass loss
(NiLACHÁCdBr2Á(DMF)2)
Mw = 853.33
1—Heating rate:
5° C min-1, 190–236/DTA
peak: 226
8.55/7.76
7.85
1—Heating rate:
5° C min-1, 236–284/DTA
peak: 244
—/20.738
21.15
2—Heating rate:
10° C min-1, 193–244/DTA
peak: 233
2—Heating rate:
10° C min-1, 244–301/DTA
peak: 249
3—Heating rate:
15° C min-1, 203–246/DTA
peak: not det.
6.82
3—Heating rate:
15° C min-1, 246–313/DTA
peak: 254
20.59
4—Heating rate:
20° C min-1, 208–252/DTA
peak: not det.
6.99
4—Heating rate:
20° C min-1, 252–318/DTA
peak: 259
20.54
5—Heating rate:
7.30
5—Heating rate:
25° C min-1, 252–322/DTA
peak: 265
20.96
25° C min-1, 209–257/DTA Average:
peak: 252
Average: 20.79 0.26
7.35 0.46
(NiLACHÁCdBr2Á(DMF)2)
Mw = 791.15
1—Heating rate:
5° C min-1, 149–201/DTA
peak: 175
9.22/8.69
8.85
1—Heating rate:
5° C min-1, 254–316/DTA
peak: 274 and 280
9.22/8.98–14.64
8.97–17.28
8.92–16.91
8.98–18.97
9.23–19.07
2—Heating rate:
10° C min-1, 155–220/DTA
3-peak: 179
2—Heating rate:
10° C min-1, 254–328/DTA
peak: 276 and 298
3—Heating rate:
15° C min-1, 158–228/DTA
peak: 183
8.90
3—Heating rate:
15° C min-1, 251–334/DTA
peak: 283 and 304
4—Heating rate:
15° C min-1, 160–233/DTA
peak: 189
9.53
4—Heating rate:
20° C min-1, 272–360/DTA
peak: 297 and 315
5—Heating rate:
9.12
5—Heating rate:
20° C min-1, 263–361/DTA
peak: 299 and 316
15° C min-1, 162–239/DTA Average:
peak: 191 9.02 0.32
Average:
9.02 0.12–17.37 1.81
coordination sphere and mass loss due to DMF removal
reaction, respectively. Therefore, the first mass loss is
attributed to this process. However, in [NiLACHÁCdBr2-
(DMF)2] complex the DMF molecules are removed from
the structure in a two-step procedure. Both of these thermal
reactions are endothermic. On the other hand, the removal
of DMF seems to take place by a single-step process in
[NiLHÁCdI2Á(DMF)2]. However if we look more carefully
at the curves, we can see that removal of DMF molecules is
in fact a two-step process in [NiLHÁCdI2Á(DMF)2] complex.
The detailed curves in Fig. 5 which depict only the
region where the mass loss takes place clearly illustrate the
fact that the [NiLACHÁCdBr2Á(DMF)2] complex also gives
a two-step DMF removal reaction. However, the other
complex [NiLHÁCdI2Á(DMF)2] gives a shoulder around
280 °C in TG and two endothermic signal around 280 and
305 °C in DTA plots. These two endothermic reactions are
not clearly visible since they occur very close to each other.
The thermos analytical data obtained from the TG curves
are listed in Table 3.
123

Two dinuclear NiII–CdII complexes of reduced ONNO-type Schiff bases
(a)
(b)
–8.8
–9.0
–9.2
–9.4
–9.6
–9.8
3.2
3.0
2.8
β
β
–10.0
–10.2
–10.4
–10.6
2.6
2.4
2.2
1.90
1.90
2.12
1.95
2.00
1.90
1.95
2.00
2.05
103.T –1/K
103.T –1/K
(c)
–12.6
(d)
2.8
2.6
2.4
2.2
2.0
1.8
1.6
–12.7
–12.8
–12.9
–13.0
–13.1
–13.2
–13.3
–13.4
β
α
1.95
103.T –1/K
2.00
2.12
2.14 2.16
2.18
103.T –1/K
2.20 2.22
2.24
(e)
–9.4
(f)
–12.8
–13.0
–13.2
–13.4
–13.6
–13.8
–14.0
–9.6
–9.8
–10.0
–10.2
–10.4
–10.6
–10.8
α
β
2.14 2.16
2.18
2.20 2.22
2.24
2.10 2.12 2.14 2.16 2.18 2.20 2.22 2.24
103.T –1/K
103.T –1/K
Fig. 6 a The linear lines obtained by OFW methods for [NiLHÁCdI2-
(DMF)2]. b The KAS results of [NiLHÁCdI2Á(DMF)2] complex: black:
g(a) = 0.2, red: g(a) = 0.3, green: g(a) = 0.4, blue: g(a) = 0.5,
brown: g(a) = 0.6, orange: g(a) = 0.7, dark green: g(a) = 0.8. c The
CR results of [NiLHÁCdI2Á(DMF)2] complex: black: 5 °C min-1, red:
10 °C min-1, green: 15 °C min-1, blue: 20 °C min-1, brown: 25 °C
min-1. d The lines obtained for [NiLACHÁCdBr2Á(DMF)2] complex
by the OFW method: black: g(a) = 0.2, red: g(a) = 0.3, green:
g(a) = 0.4, blue: g(a) = 0.5, brown: g(a) = 0.6, orange: g(a) = 0.7,
dark green: g(a) = 0.8. e The KAS results of [NiLACHÁCdBr2-
(DMF)2] complex: black: g(a) = 0.2, red: g(a) = 0.3, green:
g(a) = 0.4, blue: g(a) = 0.5, brown: g(a) = 0.6, orange:
g(a) = 0.7, dark green: g(a) = 0.8. f The CR results of [NiLACH-
CdBr2Á(DMF)2] complex: black: 5 °C min-1, red: 10 °C min-1
,
green: 15 °C min-1, blue: 20 °C min-1, brown: 25 °C min-1
123

¨
M. Sonmez et al.
123

Two dinuclear NiII–CdII complexes of reduced ONNO-type Schiff bases
Table 5 The comparison of the theoretical and experimental bond lengths and angles
(NiLACHÁCdBr2Á(DMF)2) Experimental bond
Theoretical bond
˚
lengths/A
(NiLHÁCdI2Á(DMF)2) Experimental bond
Theoretical bond
˚
lengths/A
˚
lengths/A
˚
lengths/A
N1-Ni1
2.101 (6)
2.084 (5)
1.99672
1.99227
1.91395
2.27546
1.91531
2.27531
3.09201
4.06586
2.63299
2.64888
3.23914
100.92683
100.890
82.513
N1 Ni1
2.092 (9)
2.078 (8)
2.093 (6)
2.238 (7)
2.112 (7)
2.239 (7)
2.100 (7)
2.087 (7)
2.7527 (14)
2.7447 (15)
3.3438 (17)
101.0 (3)
100.4 (3)
96.4 (3)
1.98579
1.97975
1.93202
2.26261
1.92934
2.26981
3.09347
3.29466
2.82023
2.84309
3.33114
104.875
104.697
97.662
N2-Ni1
N2 Ni1
O1-Ni1
2.070 (4)
O1 Ni1
O1-Cd1
2.215 (4)
O1 Cd1
O2-Ni1
2.067 (4)
O2 Ni1
O2-Cd1
2.227 (4)
O2 Cd1
O3dmf-Ni1
O4dmf-Ni1
Br1-Cd1
2.119 (4)
O3dmf Ni1
O4dmf Ni1
I1 Cd1
2.087 (4)
2.5257 (10)
2.5409 (10)
3.2854 (9)
100.05 (17)
99.79 (17)
83.10 (16)
90.97 (18)
172.68 (18)
172.5 (2)
Br2-Cd1
I2 Cd1
Ni1-Cd1
Ni1-Cd1
Ni1 O1 Cd1
Ni1 O2 Cd1
O2 Ni1 O1
O2 Ni1 N2
O1 Ni1 N2
O2 Ni1 N1
O1 Ni1 N1
N2 Ni1 N1
O1 Cd1 O2
O1 Cd1 Br1
O2 Cd1 Br1
O1 Cd1 Br2
O2 Cd1 Br2
Br1 Cd1 Br2
Ni1 O1 Cd1
Ni1 O2 Cd1
N2 Ni1 N1
N2 Ni1 O1
N1 Ni1 O1
N2 Ni1 O2
N1 Ni1 O2
O1 Ni1 O2
O1 Cd1 O2
O1 Cd1 I2
O2 Cd1 I2
O1 Cd1 I1
O2 Cd1 I1
I2 Cd1 I1
92.075
172.3 (3)
90.7 (3)
170.805
89.888
172.673
172.949
92.261
91.0 (3)
90.620
89.5 (2)
172.6 (3)
81.9 (3)
171.471
115.652
67.715
96.4 (2)
92.704
76.30 (14)
121.16 (10)
120.02 (11)
109.21 (10)
108.55 (10)
115.36 (4)
67.405
76.0 (2)
114.295
114.848
107.228
106.862
129.381
121.72 (17)
122.04 (19)
105.19 (17)
109.47 (18)
115.64 (4)
112.023
113.002
111.606
110.133
127.142
The presence of the first step was attributed to the for-
mation of square pyramidal Ni(II) complex as intermediate.
because of NiLH complex cannot isolated at room tem-
perature, and in this case NiLH complex cannot be stable at
250 °C. For this reason, decomposition of NiL complex
begins with the removal of the second DMF molecule from
[NiLHÁCdI2Á(DMF)2] complex. As a result, the first and
second DMF losses cannot be distinguished from each
other at the DTA curves. The removal of the first DMF
molecule is much more apparent in [NiLACHÁCdBr2ÁDMF]
complex. In addition, the first and second DMF losses can
be seen in the DTA curve of the [NiLACHÁCdBr2ÁDMF]
complex. This situation indicates that the NiLACH
mononuclear complex is more stable than the mononuclear
NiLH complex. Therefore, the difference between these
two thermal reactions was investigated by the use of
thermal kinetic methods such as nonisothermal–isocon-
versional Ozawa–Flynn–Wall (OFW) and Kissinger–Aka-
hira–Sunose (KAS) and isothermal Coats–Redfern (CR)
methods. The activation energy and the Arrhenius pre-ex-
ponential of the first thermal reaction were determined
[25–31]. OFW and KAS calculations were carried out at
heating rates of 5, 10, 15, 20 and 25 °C min-1 determining
Â
Ã
Â
Ã
NiLACH Á CdBr2 Á ðDMFÞ2 ! NiLACH Á CdBr2 Á DMF
Â
Ã
Â
Ã
þ DMFðgasÞ NiLH Á Cdl2 Á ðDMFÞ2 ! NiLH Á Cdl2 Á DMF
þ DMFðgasÞ
There are similar Schiff base complexes of Ni(II)–Zn(II)
prepared in the literature, and it was reported that there
were square pyramidal and octahedral complexes formed
depending upon the ligand concentration [5]. It was not
possible to obtain a mononuclear NiLH-type complex with
LHH2 ligand. Although a CuLH complex has been reported
to be synthesized and isolated recently [38], there was no
report about the NiLH complex in the literature. On the
other hand, the TG curves show clearly that the interme-
diate product [NiLACHÁCdBr2ÁDMF] formed during the
reaction is much more stabile because of this intermediate
remained stable between 210 and 250 °C and the second
DMF molecule immediately removed in [NiLHÁCdI2-
(DMF)] and the decomposition of the complex has began
123

¨
M. Sonmez et al.
the T values corresponding to the points at g(a) 0.2, 0.3,
0.4, 0.5, 0.6, 0.7 and 0.8, and 1/T values were plotted
against lnb for OFW and against ln(b/T2) for KAS method.
For CR, the g(a) values for each heating rate were calcu-
lated against different temperatures. So, five lines were
obtained for the five different heating rates and tempera-
tures. All these lines are depicted in Fig. 6a–f, and the Ea
and A values determined from Fig. 6a–f are listed in
Table 4.
Table 6 The electron density and relative energy levels of the central
atoms around coordination spheres
Atom
Orbital
Occupancy
Energy
(NiLACHÁCdBr2Á(DMF)2)
Ni
Ni
Ni
Ni
Ni
Cd
Cd
Cd
Cd
Cd
dxy
1.98411
1.89553
0.87339
1.96500
1.97814
1.99906
1.99979
1.99730
1.99788
1.99772
- 0.27503
- 0.26860
- 0.19839
- 0.27150
- 0.30411
- 0.60449
- 0.60620
- 0.60134
- 0.60375
- 0.60505
dxz
dyz
dx2y2
dz2
Mononuclear complexes prepared by the use of reduced
ONNO-type Schiff bases are very scarce, and Ni(II) com-
plex prepared from reduced ONNO-type Schiff bases has
not been reported yet. Recently, preparation, isolation and
characterization of a CuLH complex have been reported
[38]. However, some of the reduced ONNO-type Schiff
bases give abundant amount di-, tri- and polynuclear
complexes. The polynuclear complexes of these ligands are
highly stable. The kinetic analysis results reported in
Table 4 belong to the reaction of the removal of the first
DMF group from the structure. DTA curves clearly show
the formation of [NiLACHÁCdBr2ÁDMF] complex after the
removal of the first DMF molecule from the structure of
[NiLACHÁCdBr2Á(DMF)2] complex, and then, second DMF
molecule removes from the structure. This case is different
for the [NiLHÁCdBr2ÁDMF] complex. The final temperature
of the second DMF molecule removal reaction is not clear.
Thermokinetic analysis results makes it apparent that
[NiLACHÁCdI2Á(DMF)2] complex is more stable than
[NiLHÁCdI2Á(DMF)2]. The thermokinetic results for the
reactions of two complexes involving the cleavage of a
DMF molecule are given in Table 4. The Ea value for the
reaction of [NiLACHÁCdI2Á(DMF)2] is significantly higher
than the one for the reaction of [NiLHÁCdI2Á(DMF)2]. This
case clearly indicates that the thermal stability of
[NiLACHÁCdI2Á(DMF)2] is higher. The magnitude of the
activation energy is the indication of the stability of the
compound. The greater activation energy corresponds to
higher thermal stability of the compound. The results
reported in Table 4 are different from each other. Espe-
cially, the data found by the isothermal CR method are
highly different than the data obtained by these of non
isothermal methods. Although the Ea values obtained from
by the use of OFW and KAS methods were found to be
comparable, the values of the pre-exponential constants
were erratic and were not comparable. The reason for this
discrepancy was most probably the immediate removal of
the second DMF molecules just after the removal of the
first molecule leaving a highly unstable mononuclear
complex behind, which immediately decomposes with the
removal of the second DMF group. The [NiLACHÁCdBr2-
DMF] complex formed after the removal of DMF molecule
from the structure of [NiLACHÁCdBr2Á(DMF)2] is much
more stabile that the corresponding complex of
dxy
dxz
dyz
dx2y2
dz2
(NiLHÁCdI2Á(DMF)2)
Ni
Ni
Ni
Ni
Ni
Cd
Cd
Cd
Cd
Cd
dxy
1.95486
1.57125
1.50882
1.81378
1.82272
1.99836
1.99882
1.99785
1.99885
1.99832
- 0.27368
- 0.24083
- 0.25378
- 0.25943
- 0.28358
- 0.60785
- 0.60919
- 0.60678
- 0.60782
- 0.60867
dxz
dyz
dx2y2
dz2
dxy
dxz
dyz
dx2y2
dz2
[NiLHÁCdI2ÁDMF] formed with a similar manner from the
[NiLHÁCdI2Á(DMF)2] complex. This is verified with the TG
data where the boundaries of the first and second thermal
DMF reaction are clearly visible in TG curves of
[NiLACHÁCdBr2ÁDMF] complex. We think that the dif-
ferences can be been explained by the results obtained from
theoretical programs. Therefore, the theoretical bond
lengths, bond angles and the HOMO–LUMO diagrams
were calculated by the use of DFT/B3LYP/LanL2DZ
algorithm embedded in Gaussian 09 software. In addition,
the occupancy level of the d orbitals of the central atoms
and relative energy levels were calculated with natural
bond-order (NBO) analysis by using the atomic coordinates
obtained from X-ray data as input. The bond lengths, bond
angles in the coordination sphere and the occupancy levels
of the 3d orbitals of Ni(II) and 4d orbitals of Cd(II) are
given in Tables 5 and 6, respectively. The steric conditions
created by the methyl groups effect the overlapping feature
of the nitrogen donor groups. Therefore, the high proba-
bility of HOMO orbitals around central Ni(II) ion of
[NiLACHÁCdBr2Á(DMF)2] complex is shown in Fig. 7. In
contrary, this probability for the other complex is weak.
The calculated average energy levels of HOMO and
LUMO orbitals for both complexes show that [NiLACH-
CdBr2Á(DMF)2] complex is more stable. The HOMO,
123

Two dinuclear NiII–CdII complexes of reduced ONNO-type Schiff bases
[NiLACH.CdBr2.DMF]
[NiLH.CdI2.(DMF)2]
HOMO, calculated energy level: –5.888 eV
HOMO, calculated energy level: –5.709 eV
LUMO, calculated energy level: –2.072 eV
LUMO, calculated energy level: –2.105 eV
Fig. 7 The HOMO and LUMO orbitals of the complexes prepared
LUMO energy levels and DE for [NiLACHÁCdBr2Á(DMF)2]
complex are - 5.888, - 2.072 and 3.816 eV, respectively.
These values for the other complex are - 5.709, - 2.105
and 3.604 eV. As expected, DE value of the [NiLACH-
˚
3.09 A in theoretical calculations. The same situation
exists in HOMO–LUMO diagram. Figure 7 indicates that
the central Ni(II) ion of [NiLACHÁCdBr2Á(DMF)2] complex
overlaps in a stronger manner. Figure 7a shows that the
central ion of compound [NiLACHÁCdBr2Á(DMF)2] makes
a much stronger overlapping with the HOMO orbitals.
Figure 7b, on the other hand, indicates that the overlapping
of the central atom of compound [NiLHÁCdI2Á(DMF)2] is
not as strong as the corresponding ion of [NiLACH-
CdBr2Á(DMF)2] complex. The experimental bond lengths
of N1-Ni and N2-Ni of [NiLHÁCdI2Á(DMF)2] complex
CdBr2Á(DMF)2]
complex
is
greater
than
[NiLHÁCdI2Á(DMF)2].
The most probable explanation of this difference is the
fact that after being located between Cd(II) ions extracts
electrons from the oxygen atoms decrease the electron
density going from these oxygen atoms to nickel ion. That
is why the central Ni(II) atom binds two solvent molecules.
The bond lengths indicate that they are coordinatively
bounded. When we look at the bond lengths given in
Table 6, it is seen that the biggest difference between the
experimental and theoretically calculated values was
between the oxygen atoms of the coordinated DMF groups
and the central Ni(II) ion. The experimental values were
˚
(2.093 and 2.112 A) are longer than the corresponding
bonds in [NiLACHÁCdBr2Á(DMF)2] complex (2.070 and
˚
2.067 A). It is possible that the two methyl groups increase
electron-donating capacities of the nitrogen donors. That is
why it can be claimed that the intermediate product of
[NiLACHÁCdBr2Á(DMF)2] complex is more stable than the
intermediate product of [NiLACHÁCdBr2ÁDMF]. The
˚
determined as 2.119 and 2.087 A come out as 4.06 and
123

¨
M. Sonmez et al.
occupancy levels of the central ions obtained by NBO
analysis are listed in Table 6. It is not logical to expect any
energy differences between 4d orbitals of the both coor-
dination compound since Cd(II) ion is in d10 state. In fact,
since the occupancy levels of 4d orbitals of Cd(II) ion are
very close to 2.00, the energy levels of 4d orbitals are not
different from each other. If we think that the O2N2 donors
are coordinated along x and y and the oxygens of the DMF
molecules z axes, it is obvious that the most effected
orbitals are dx2-y2, dz2 and dxy orbitals. According to the
data listed in Table 6, this seems to be the case for
[NiLACHÁCdBr2Á(DMF)2] complex. However, the dx2-y2
orbital of [NiLHÁCdI2Á(DMF)2] complex does not follow
this trend. This is an evidence that the locations of the
nitrogen donors of the [NiLHÁCdI2Á(DMF)2] compound are
not suitable for overlapping. That is causes the resulting
intermediate of formed in the thermal analyses being higly
unstable and decompose immediately. On the other hand,
thermogravimetric data of the [NiLACHÁCdBr2Á(DMF)2]
complex do not explicitly prove that the compound
NiLACH formed after the removal of DMF groups is highly
stabile. What it proves is that it is at least more stable than
the corresponding NiLH of the other complex. It is a known
fact that one cannot expect a complete accordance with the
thermokinetic analysis if the compound gives no
stable product as a result of thermal dissociation process.
The thermal kinetic applications are based upon certain
assumptions [24]. The validity of the Kissinger equation
has been disputed in recent days [39].
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