Synthesis of some Schiff base metal complexes involving para substituted aromatic aldehydes and glycylglycine: Spectral, electrochemical, thermal and surface morphology studies

Article abstract of DOI:10.1016/j.molstruc.2010.08.040

Two Schiff base ligands, cumi-gg(L) and pcb-gg(L¹) were prepared via condensation of cuminaldehyde (p-isopropylbenzaldehyde)/p- chlorobenzaldehyde and glycylglycine. The ligands were characterized based on elemental analysis, mass, ¹

Full text of DOI:10.1016/j.molstruc.2010.08.040

Journal of Molecular Structure 983 (2010) 112–121
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis of some Schiff base metal complexes involving para substituted
aromatic aldehydes and glycylglycine: Spectral, electrochemical, thermal
and surface morphology studies
⇑
D. Arish, M. Sivasankaran Nair
Department of Chemistry, Manonmaniam Sundaranar University, Tirunelveli 627 012, India
a r t i c l e i n f o
a b s t r a c t
Two Schiff base ligands, cumi-gg(L) and pcb-gg(L1) were prepared via condensation of cuminaldehyde
(p-isopropylbenzaldehyde)/p-chlorobenzaldehyde and glycylglycine. The ligands were characterized
based on elemental analysis, mass, 1H and 13C NMR, IR and UV–Vis spectra. Co(II), Ni(II), Cu(II), Zn(II)
and Ru(II) metal complexes are reported and characterized based on elemental analysis, mass, 1H and
13C NMR, molar conductance, IR, UV–Vis, magnetic moment, CV, ESR and thermal analyses, powder
XRD and SEM. All the complexes were found to be non-electrolytic in nature. IR spectra show that the
ligands are coordinated to the metal ions in a tridentate manner. The geometrical structures of these
complexes are found to be octahedral. The thermal behavior of the synthesized complexes indicates
the presence of lattice as well as coordinated water molecules in the complexes. The SEM image of
[CoL1(H2O)3] complex exhibit nano rod structure.
Article history:
Received 24 July 2010
Received in revised form 20 August 2010
Accepted 22 August 2010
Available online 26 August 2010
Keywords:
Schiff base
IR
CV
ESR
Ó 2010 Elsevier B.V. All rights reserved.
Thermal analysis
SEM
1. Introduction
[24–26], the present study describes the synthesis and character-
ization of two novel Schiff base ligands viz cuminaldehyde (p-iso-
Major advances have been made on the study of transition me-
tal complexes with aromatic carbonyl Schiff base ligands due to
their interesting properties and potential applications in the cata-
lytic, analytical and biological fields [1–7]. Ru(II) Schiff base com-
plexes were found to be useful catalysts in many reactions [8–
10]. There is a continuing interest in metal complexes of amino
acid Schiff bases [11,12], because of the presence of both hard
nitrogen and oxygen and soft sulphur donor atoms in the back-
bones of these ligands. They readily coordinate with transition me-
tal ions yielding stable and intensely coloured metal complexes
and have been shown to exhibit interesting physical, chemical,
and potentially beneficial chemotherapeutic properties [13–16].
For e.g., Co(II), Ni(II) and Cu(II) complexes of Schiff bases derived
from 4-hydroxysalicylaldehyde and amino acids have been shown
to have stronger anticancer activity against Ehrlich ascites carci-
noma (EAC) [17]. Many reports are available for the preparation
and properties of model complexes with amino acid Schiff bases.
However, little attention has been paid to systems in which the
Schiff bases are derived from dipeptides, and few such compounds
have been synthesized and structurally characterized [18–23]. In
continuation to our interest in metal complexes of Schiff bases
propylbenzaldehyde)-glycylglycine (cumi-gg) and p-chlorobenz-
aldehyde-glycylglycine (pcb-gg)) and their Co(II), Ni(II), Cu(II),
Zn(II) and Ru(II) complexes.
2. Experimental
2.1. Materials
Glycylglycine was purchased from Sigma and used without fur-
ther purification. Cuminaldehyde and p-chlorobenzaldehyde were
obtained from Himedia. Co(II), Ni(II), Cu(II), Zn(II) and Ru(III) chlo-
rides were Merck samples. All other reagents and solvents were
purchased from commercial sources and were of analytical grade.
2.2. Synthesis of cumi-gg (L)
A
solution of glycylglycine (10 mmol) and KOH pellets
(10 mmol) in 50 mL of MeOH is kept under continuous stirring in
a 100 mL RB flask. A solution of cuminaldehyde (10 mmol) in
50 mL MeOH is then added slowly to the flask. The reaction mix-
ture was vigorously stirred at room temperature for 15 min and
then refluxed at 70–80 °C for 8 h. The yellow solution is reduced
to 1/3 of its original volume by rotary evaporation. The concen-
trated filtrate thus obtained is poured into diethyl ether. A yellow
⇑
Corresponding author. Tel.: +91 944 3540046; fax: +91 462 23334363.
E-mail address: msnairchem@rediffmail.com (M. Sivasankaran Nair).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.08.040

D. Arish, M. Sivasankaran Nair / Journal of Molecular Structure 983 (2010) 112–121
113
precipitate was formed, which is collected by vacuum filtration
and washed several times with anhydrous ether and then dried
in vacuo over anhydrous CaCl2. The yield of the isolated ligand is
found to be 72%.
several times with cold EtOH, ether and then dried in vacuo over
anhydrous CaCl2.
2.6. Physical measurements
2.3. Synthesis of pcb-gg (L1)
Elemental analysis was done using a Perkin–Elmer elemental
analyzer. The Mass spectra of the Schiff base ligand and its com-
plexes were recorded on a JEOL SX 102/DA-600 mass spectrometer.
The 1H and 13C NMR spectra of the Schiff base ligand were recorded
in JEOL GSX 400 FT-NMR spectrometer. Molar conductance of the
complexes were measured in MeOH (10À3 M) solutions using a
coronation digital conductivity meter. IR spectra were recorded
in KBr disc on a JASCO FT/IR-410 spectrometer in the 4000–
400 cmÀ1 region. The electronic spectra were recorded on a Perkin
Elmer Lambda-25 UV–Vis spectrometer. Room temperature mag-
netic measurements were performed on a Guoy balance by making
diamagnetic corrections using Pascal’s constant. The X-band ESR
spectrum of Cu(II) complex was recorded on a Varian E112 X-band
spectrometer using TCNE as standard. Cyclic voltammetric mea-
surements were carried out in a Bio-Analytical system (BAS) model
CV-50 W electrochemical analyzer. The three electrode cell com-
prised of a reference Ag/AgCl, auxiliary platinum and working
glassy electrodes. Tetrabutylammonium perchlorate was used as
supporting electrolyte. Thermal analysis was carried out on SDT
Q 600/V8.3 build 101 thermal analyzer with the following condi-
tions; temperature calibration-pure metal standards, sample mass
6–8 mg, heating rate 20 °C/min and nitrogen atmosphere (flow rate
20 mL/min). Powder XRD was recorded on a Rigaku Dmax X-ray
A
solution of glycylglycine (10 mmol) and KOH pellets
(10 mmol) in 50 mL of MeOH is kept under continuous stirring in
a 100 mL RB flask. A solution of p-chlorobenzaldehyde (10 mmol)
in 50 mL absolute MeOH is then added slowly to the flask. The
reaction mixture was vigorously stirred and then refluxed at 70–
80 °C for 8 h. After 2 days an air sensitive dark yellow precipitate
was formed, which is collected by vacuum filtration and washed
several times with anhydrous ether and then dried in vacuo over
anhydrous CaCl2. The yield of the isolated ligand is found to be 80%.
2.4. Synthesis of Co(II), Ni(II), Cu(II) and Zn(II) Schiff base complexes
A solution of cumi-gg/pcb-gg (2 mmol) in MeOH (20 mL) was
added to a solution of metal(II) chloride (2 mmol) in 20 mL of aque-
ous MeOH, and the reaction mixture was stirred and then refluxed
for 2 h. The resulting solution was cooled to room temperature and
the volume was reduced to half of the initial volume under reduced
pressure. The precipitate was filtered off, washed several times with
cold EtOH, ether and then dried in vacuo over anhydrous CaCl2.
2.5. Synthesis of Ru(II) Schiff base complexes
diffractometer with Cu K
a radiation (kK = 1.5406 Å). SEM images
a
were recorded in a Hitachi SEM analyzer.
RuCl3Á3H2O (1 mmol) and an excess LiCl (1 g) were dissolved in
ethanol (20 mL) and the mixture was refluxed for 30 min. A solu-
tion of Schiff base ligand cumi-gg/pcb-gg (1 mmol) was added drop
wise to the above dark brown ruthenium solution. Immediately, a
blackish green precipitate was formed, which was further refluxed
for 2 h on a water bath. The precipitate was filtered off, washed
3. Result and discussion
The analyticaland physical data ofcumi-gg(L)andpcb-gg (L1)and
their complexes are listed in Table 1. The proposed structure of the
Table 1
Analytical and physical data of the Schiff ligand and its complexes.
Compound
Empirical formula
Colour
Elemental analysis found (calcd)%
K
c (OhmÀ1 cm2 molÀ1
)
kmax (nm)
leff
(BM)
C
H
N
M
–
Cumi-gg (L)
KC14H17N2O3
Yellow
55.87
5.65
9.45
–
220, 268, 302, 356
630, 690
–
(55.98)
(5.70)
(9.33)
[CoL(H2O)3]
CoC14H22N2O6
NiC14H22N2O6
CuC14H22N2O6
ZnC14H22N2O6
RuC14H24N2O7
KClC11H10N2O3
CoClC11H15N2O6
NiClC11H15N2O6
CuClC11H19N2O8
ZnClC11H17N2O7
RuClC11H19N2O8
Brown
45.21
(45.05)
6.01
(5.94)
7.43
(7.51)
15.63
(15.79)
12
09
15
07
12
5.11
3.23
1.92
Dia
[NiL(H2O)3]
Light green
44.93
(45.08)
6.01
(5.94)
7.42
(7.51)
15.68
(15.73)
1100, 710, 400
720
[CuL(H2O)3]
Deep
Green
44.39
(44.50)
5.68
(5.87)
7.56
(7.41)
16.74
(16.82)
[ZnL(H2O)3]
Light yellow
Blackish green
Bright yellow
Brown
44.73
(44.28)
5.48
(5.84)
7.66
(7.38)
17.01
(17.22)
345
[RuL(H2O)3]ÁH2O
Pcb-gg (L1)
38.65
(38.80)
5.72
(5.58)
6.39
(6.46)
23.25
(23.32)
420, 530, 610
250, 270, 328
630, 692
Dia
(45.06)
(45.13)
(3.32)
(3.44)
(9.68)
(9.57)
–
–
–
–
–
[CoL1(H2O)3]
[NiL1(H2O)3]
(36.37)
(36.13)
(4.03)
(4.14)
(7.69)
(7.66)
(16.28)
(16.12)
08
12
15
04
08
5.03
2.98
2.01
Dia
Green
(36.07)
(36.16)
(4.08)
(4.14)
(7.82)
(7.67)
(16.17)
(16.06)
1100, 710, 380
850
[CuL1(H2O)3]Á2H2O
[ZnL1(H2O)3]ÁH2O
[RuL1(H2O)3]Á2H2O
Green
(32.65)
(32.52)
(4.79)
(4.71)
(6.98)
(6.90)
(15.38)
(15.64)
Light yellow
Blackish green
(33.59)
(33.87)
(4.32)
(4.39)
(7.32)
(7.18)
(16.72)
(16.76)
320
29.68
(29.77)
4.44
(4.32)
6.39
(6.31)
22.85
(22.77)
423, 525, 620
Dia

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D. Arish, M. Sivasankaran Nair / Journal of Molecular Structure 983 (2010) 112–121
Schiff base ligands are shown in Fig. 1. The Schiff base ligands are air
sensitive in nature and soluble in all common organic solvents. The
CuLÁ3H2O complex is air sensitive, hydroscopic in nature and soluble
in water, DMF and DMSO, while other complexes are stable towards
air and moisture and soluble in acetonitrile, DMF and DMSO. The mo-
lar conductance values (Table 1) of metal complexes measured in
DMSO at 10À3 M reveal their non-electrolytic nature [27].
respectively in Fig. 2a and b. 1H NMR spectra of cumi-gg and pcb-
gg show a peak at 8.48 and 8.50 ppm characteristic of azomethine
proton (ACH@NA). The peaks at 9.98 and 10.08 ppm are assignable
to the peptide linkage ANHA proton for cumi-gg and pcg-gg, respec-
tively. The aromatic ring protons are observed in the 7.1–8.2 ppm
range as expected. In the 1H NMR spectrum of Zn(II) complexes,
the –CH@NA proton peak is slightly shifted to downfield. This differ-
ence in (ACH@NA) peak position could arise due to the coordination
of its neighbouring nitrogen atom which indicates the metal to coor-
dinate the ligand through azomethine nitrogen atom. The peptide
linkage ANHA proton disappears in the spectrum of Zn(II) com-
plexes. This supports the proposal that the ligands have coordinated
with the metal ion in the deprotonated form. In addition, the spectra
of ZnLÁ3H2O and ZnL1Á4H2O complexes show a broad peak centered
at 4.73 and 4.86 ppm, respectively. There are characteristic of water
molecule present in the complexes.
3.1. Mass spectra
The EI mass spectrum of the Schiff base ligand, cumi-gg (L) and
pcb-gg (L1) shows a well-defined molecular ion peak at m/z =
301.26 (Relative Intensity = 23%) and 292.87 (18%), respectively.
There are consistent with the proposed molecular formulae of
the ligands. The FAB mass spectrum of CoLÁ3H2O, NiLÁ3H2O,
CuLÁ3H2O, ZnLÁ3H2O and RuLÁ4H2O complexes shows a peak at
m/z 375.46 (7%), 373.31 (11%), 378.50 (12%), 382.27 (14%) and
433.37 (29%) respectively, corresponding to their molecular
weight. The spectrum of CoL1Á3H2O, NiL1Á3H2O, CuL1Á5H2O,
ZnL1Á4H2O and RuL1Á5H2O complexes shows a molecular ion peak
(M+) at m/z 366.13 (12%), 368.59 (11%), 407.11 (8%), 390.78 (26%)
and 443.29 (4%), respectively. The mass spectrum of all the com-
plexes indicates that the complexes are monomeric confirming
the metal to ligand ratio to be 1:1 in the complexes.
The 13C NMR spectrum of Schiff base ligands and their Zn(II) com-
plexes revealed the presence of expected number of signals corre-
sponding to different types of carbon atoms. The 13C NMR
spectrum of cumi-gg and pcb-gg shows
a peak at 164.29,
175.85 ppm for cumi-gg and 171.37, 181.45 ppm for pcb-gg respec-
tively. There are assignable to azomethine carbon (ACH@NA) and
carboxylato carbon. This peaks are slightly shifted to down field re-
gion in the Zn(II) complexes (Table 2) indicating involvement of azo-
methine nitrogen and carboxylato oxygen atoms on coordination.
3.2. NMR spectra
3.3. IR spectra
The 1H NMR and 13C NMR spectral data of the Schiff base
ligands and their Zn(II) complexes are given in Table 2. The 1H
and 13C NMR spectra of cumi-gg and its Zn(II) complex is shown
The IR spectral data of the Schiff base ligands and their com-
plexes are given in Table 3. IR spectrum of cumi-gg and pcb-gg
Fig. 1. Proposed structure of Schiff base ligands (a) cumi-gg and (b) pcb-gg.
Table 2
1H and 13C NMR spectral data of Schiff base ligands and their Zn(II) complexes.
Ligand/
Nucleus ACH3
ACH2
ACH
Aromatic (ACH)
ACH@N
ANH
AC@O
complexes
Cumi-gg
Zn(II)
1H
1.312 (d,
J = 6.9 Hz, 6H)
23.610
4.014 (s, 2H) 5.472 (d,
J = 14.7 Hz, 2H)
43.13, 53.691
2.995 (m, 7.2–7.6 (d, J = 8.1 Hz, 2H; d,
8.488 (s,
1H)
164.291
9.984 (s,
1H)
–
–
1H)
J = 7.8 Hz, 2H
13C
33.880
126–152
171.626 (pep)
175.851 (carbo)
1H
1.301 (d,
J = 6.9 Hz, 6H)
23.653
4.167 (s, 2H) 5.401 (s, 2H)
43.462, 53.714
2.975 (m, 7.1–7.8 (d, J = 8.1 Hz, 2H; d,
8.602 (s,
1H)
165.045
–
–
–
1H)
J = 7.5 Hz, 2H)
13C
33.903
126–152
171.679 (pep)
176.624 (carbo)
Pcb-gg
Zn(II)
1H
–
–
4.272 (s, 2H) 5.526 (d,
J = 14.9 Hz, 2H)
46.358, 54.397
–
–
7.4–8.1 (d, J = 8.1 Hz, 2H; d,
J = 7.8 Hz, 2H)
129–152
8.501 (s,
1H)
171.370
10.085(s,
1H)
–
–
13C
175.971(pep)
181.459 (carbo)
1H
–
–
4.306 (s, 2H) 5.665 (s, 2H)
46.433, 54.415
–
–
7.4–8.2 (d, J = 8.1 Hz, 2H; d,
J = 7.5 Hz, 2H)
129–152
8.742 (s,
1H)
165.939
–
–
–
13C
176.001 (pep)
182.329 (carbo)

D. Arish, M. Sivasankaran Nair / Journal of Molecular Structure 983 (2010) 112–121
115
show the strong band respectively at 1665 and 1638 cmÀ1. These
are assigned to azomethine stretching frequency. During complex-
ation, these bands are shifted to lower frequency indicating the
coordination of azomethine nitrogen to the metal ion. In the spec-
trum of Schiff bases, the sharp band present in the region ꢀ3300
and ꢀ1520 cmÀ1 is due to peptide NAH stretching frequency
Fig. 2. (a) 1H NMR spectrum of cumi-gg (L) and (b) [ZnLÁ(H2O)3].
Table 3
IR spectral data of the Schiff base ligands and their complexes (cmÀ1).
Compound
mazo (C@N)
m
asym(COOÀ)
m
sym(COOÀ)
mpeptide(NAH)
m(H2O)
m
(MAO)
m(MAN)
Cumi-gg (L)
[CoL(H2O)3]
[NiL(H2O)3]
[CuL(H2O)3]
1665
1647
1645
1640
1653
1645
1638
1632
1628
1628
1630
1625
1608
1596
1590
1592
1598
1592
1590
1584
1582
1584
1580
1578
1385
1371
1370
1375
1370
1372
1378
1372
1368
1371
1365
1365
3298
–
–
–
–
–
3270
–
–
–
–
–
–
–
–
3387
3385
3398
3390
4000
–
3395
3380
4010
4003
4008
520
526
534
522
520
–
528
524
530
526
530
434
440
438
430
434
–
425
427
431
429
435
[ZnL(H2O)3]
[RuL(H2O)3]ÁH2O
Pcb-gg (L1)
[CoL1(H2O)3]
[NiL1(H2O)3]
[CuL1(H2O)3]Á2H2O
[ZnL1(H2O)3]ÁH2O
[RL1(H2O)3]Á2H2O

116
D. Arish, M. Sivasankaran Nair / Journal of Molecular Structure 983 (2010) 112–121
[28]. In the complexes, the peptide m(NH) bands disappeared indi-
cating the metal ion to coordinate through deprotonated nitrogen
atom [29]. The new broad band appeared at ꢀ3400 cmÀ1 can be
attributed to the stretching vibration of the water molecule. Fur-
ther, the band at ꢀ800 cmÀ1 in the complexes is assigned to coor-
dinated water molecule [30]. The strong bands present in the
region 1608 and 1590 cmÀ1 respectively, cumi-gg and pcb-gg can
be assigned to an asymmetric stretching frequency of carboxylato
group. The Schiff base ligands also display bands at 1385 and
1378 cmÀ1 respectively, due to symmetric stretching vibration of
carboxylato group [28]. On complexation, the asymmetric and
symmetric stretching bands are shifted to lower frequency for all
the complexes, which reveals the formation of a linkage between
the metal ion and carboxylato oxygen atom. Moreover, the large
difference (ꢀ200) between the asymmetric and symmetric stretch-
ing modes indicates the monodentate binding of the carboxylato
group in the complexes [31].
CoL1Á3H2O, respectively (normal range for octahedral Co(II) com-
plexes is 4.3–5.2 BM), which is indicative of octahedral geometry
[34]. The electronic spectrum of the Ni(II) complexes show three
bands in the region ꢀ1100, ꢀ700 and ꢀ400 nm (Table 1), attribut-
able to 3A2g(F) ? 3T2g(F), 3A2g(F) ? 3T1g(F) and 3A2g(F) ? 3T1g(P)
transitions, respectively, suggesting an octahedral geometry
around Ni(II) atom [35]. The NiLÁ3H2O and NiL1Á3H2O complexes
reported herein are found to have a room temperature magnetic
moment value of 3.23 and 2.98 BM respectively, which are in the
normal range observed for octahedral Ni(II) complexes (leff 2.9–
3.3 BM) [34]. The Cu(II) complexes in their spectra display a broad
band in the ꢀ800 nm region which can be assigned to 2Eg ? 2T2g
transition, indicating the complexes to have distorted octahedral
geometry [32]. The magnetic moment value of 1.92 and 2.01 BM
respectively for CuLÁ3H2O and CuL1Á5H2O, falls within the range
normally observed for octahedral Cu(II) complexes [33]. The
ground state of Ru(II) in an octahedral environment is 1A1g, arising
3
The spectrum of all the metal complexes show new bands in the
520–540 cmÀ1 and 420–440 cmÀ1 regions, which may probably be
due to the formation of MAO and MAN bonds, respectively [28].
from the t2g configuration. The exited state terms are T1g
,
3T2g
,
1T1g and T2g, hence four bands corresponding to the transition
1
1A1g ? 3T1g 1A1g ? 3T2g 1A1g ? 1T1g and 1A1g ? 1T2g are possible
,
,
in order of increasing energy. However, the electronic spectrum
of Ru(II) octahedral complexes shows in general three to four
absorption bands in the region 719–254 nm [36]. The Ru(II) com-
plexes in the present investigation shows an absorption bands at
ꢀ420, ꢀ525 and ꢀ620 nm (Table 1). This demonstrates an octahe-
dral geometry for the Ru(II) complex. Further, the magnetic mo-
ment values of these complexes manifest their diamagnetic
nature with +2 oxidation state.
3.4. Electronic spectra and magnetic measurements
The spectra of free cumi-gg and pcb-gg exhibit a broad band at
380 and 328 nm, respectively, which can be assigned to p–
pà tran-
sition of the azomethine (>C@N) chromophore. In addition, the
other intense absorption band at higher energy, 225–270 nm is
due to the
p–
pà and n–pà transition of the benzene ring of the
Schiff base ligands. The electronic spectrum of Co(II) complexes
show two absorption bands (Table 1) at 600–700 nm region, which
are assignable to 4T1g(F) ? 4A2g(F) and 4T1g(F) ? 4T2g(F) transi-
tions in an octahedral environment [32,33]. The magnetic suscep-
tibility value is found to be 5.11 and 5.03 BM for CoLÁ3H2O and
3.5. Electrochemistry
The cyclic voltammograms were recorded in acetonitrile solu-
tion at a scan rate of 100 mV sÀ1 in the potential range +2.0 to
Fig. 3. Cyclic voltammagram of (a) [CoL(H2O)3]; (b) [CoL1(H2O)3]; (c) [NiL(H2O)3]; (d) [CuL(H2O)3] complexes.

D. Arish, M. Sivasankaran Nair / Journal of Molecular Structure 983 (2010) 112–121
117
À2.0 V. The cyclic voltammogram of CoLÁ3H2O, CoL1Á3H2O,
CuLÁ3H2O and NiLÁ3H2O complexes are shown in Fig. 3a–d. The
Schiff base ligands and their Zn(II) complexes do not show any
peaks in this potential range under similar conditions. The cyclic
voltammogram of CoLÁ3H2O shows (Fig. 3a) a well-defined redox
process corresponding to the formation of the quasi-reversible
Co(II)/Co(I) couple. The cathodic peak at À0.848 V versus Ag/AgCl
and the associated anodic peak at À0.640 V corresponds to the
Co(II)/Co(I) couple. The peak-to-peak separation (DEp) indicates
quasi-reversible one electron transfer process. The redox property
of CoL1Á3H2O displayed electrochemically irreversible Co(II)/Co(I)
reduction at Epc À0.703 V. During the reverse scan the oxidation
Fig. 4. ESR spectrum of [CuL(H2O)3] complex (a) 300 K and (b) 77 K.

118
D. Arish, M. Sivasankaran Nair / Journal of Molecular Structure 983 (2010) 112–121
of Co(I)/Co(II) occurs in the potential range Epa +0.25. The peak-to-
peak separation ( Ep) is 675 mV indicating the process to be irre-
molecules. However, the complexes in the frozen state (77 K) exhi-
bit anisotropic signals with g values: (i) g// = 2.23 and g\ = 2.05
respectively for CuLÁ3H2O and (ii) g// = 2.28 and g\ = 2.06 respec-
tively for CuLÁ5H2O, which is characteristic for axial symmetry.
The trend g// > g\ > ge shows that the unpaired electron is localized
in the d2x À d2y orbital of Cu(II) in complex [37]. The exchange cou-
pling interaction between two Cu(II) ions is explained by Hath-
away [38] expression G = (g|| À 2)/(g\ À 2). If the G value is larger
than 4, the exchange interaction is negligible because the local
tetragonal axes are aligned parallel or slightly misaligned. If the va-
lue is less than 4, the exchange interaction is considerable and the
local tetragonal axes are misaligned. The observed G for CuLÁ3H2O
and CuL1Á5H2O is 4.35 and 4.66 respectively, suggesting that the lo-
cal tetragonal axes are aligned parallel or slightly misaligned and
consistent with a d2x À dy2 ground state. Moreover, the absence of
D
versible. The electrochemistry of NiLÁ3H2O is similar to that of
NiL1Á3H2O, anodic waves are seen at À0.998 and at À0.983 V and
the associated cathodic peaks at À0.543 and À0.536 V respectively,
corresponding to the formation of the quasi-reversible one-elec-
tron reduction Ni(II)/Ni(I) couple.
The cyclic voltammogram of the CuLÁ3H2O complex displayed
two reduction couples at +0.054 V and À0.668 V versus Ag/AgCl
with the corresponding anodic wave for the first reduction and
without the corresponding anodic wave for the second reduction
on the reverse scan. The former has a lower peak separation value
of 0.030 indicating totally reversible character for the two electron
transfer reaction of metal-based Cu(II)/Cu(0) couples and the later
one can be assigned to Cu(II)/Cu(I) irreversible reduction process.
The CuL1Á5H2O complex displayed two reduction couples at
+0.193 V and À0.889 V versus Ag/AgCl with the corresponding
anodic waves at +0.556 and at À0.535 V on the reverse scan. The
a half field signal at 1600 G corresponding to
DM = 2 transitions
indicates the absence of any Cu–Cu interaction in the complex
[39]. Kivelson and Neiman [40] showed that for an ionic environ-
ment g|| is normally 2.3 or larger, but for covalent environment
g|| is less than 2.3. The observed g|| value for the Cu(II) complexes
suggest that the environment is covalent.
peak separation values (DEp = 0.363 and 0.354 V) indicate totally
quasi-reversible character for the one electron transfer reaction
of metal-based Cu(II)/Cu(I) and Cu(I)/Cu(0) couples. Cyclic voltam-
mogram of the RuLÁ4H2O and RuL1Á5H2O complexes show one qua-
si-reversible redox processes occurring at negative potential and
3.7. Thermal analysis
with a peak-to-peak separation (DEp value) of 230 and 253 mV
respectively. The redox process occurs with the cathodic peak po-
tential at À0.870 and À0.856 V and anodic peak potential at
À0.688 and À0. 527 V.
The thermal stability data of the complexes are listed in Table 4.
The CoLÁ3H2O, NiLÁ3H2O, CuLÁ3H2O and ZnLÁ3H2O complexes un-
dergo similar decomposition mainly in two stages. The first stage
takes place in the 160–290 °C ranges with an endothermic DTA
peak between 160 and 200 °C. The mass loss observed (Table 4)
in this step corresponds to dehydration of three coordinated water
molecule. The final decomposition step is represented by the re-
moval of complete organic ligand moiety in the 360–630 °C ranges
with the formation of metal oxide as the final product.
3.6. Electron spin resonance spectra
The X-band ESR spectra of Cu(II) complexes of cumi-gg and pcb-
gg were recorded on a powder solid at 300 and 77 K. The represen-
tative spectrum of CuLÁ3H2O complex at 300 and 77 K are shown in
Fig. 4a and b. The spectrum at 300 K shows one intense absorption
band at high field, which is isotropic due to the tumbling of the
The TG curves of the complexes CoL1Á3H2O and NiL1Á3H2O show
a weight loss 14.52% (cal.14.77%) and (14.57%) (cal. 14.78%) in the
Table 4
Thermogravimetric data of Schiff base metal complexes.
Complex
Temperature range t (°C)
% weight loss
Obs. (calcd)
DTA peak t (°C)
Process
[CoL(H2O)3]
160–286, 365–610, >610
14.02(14.47), 65.23(65.44), 20.71(20.09)
14.13(14.48), 65.13(65.49), 20.68(20.02)
14.51(14.29, 65.32(65.65), 21.69(21.05)
14.38(14.22), 64.02(64.33), 21.86(21.43)
195a, 341b, 511b,
617b
À3H2O(coord), loss of organic
moiety,
CoO
b
[NiL(H2O)3]
[CuL(H2O)3]
[ZnL(H2O)3]
176–280, 368–630, >630
188–293, 360–622, >622
185–282, 365–616, >616
178a, 380b, 540
610
,
À3H2O(coord), loss of organic
b
moiety,
NiO
175 a, 380 b, 549
,
À3H2O(coord), loss of organic
b
b
623
moiety,
CuO
167 a, 362 b, 534
À3H2O(coord), loss of organic
moiety,
ZnO
ÀH2O(lattice)
a
[RuL(H2O)3]ÁH2O
60–98,153–266, >359
4.07(4.15), 12.37(12.46),
–
14.52(14.77), 68.85(69.10), 20.72(20.49)
b102 a, 197
,
367 b, 607 b,657
224 a, 430 b, 546
À3H2O(coord), unassigned
À3H2O(coord), loss of organic
moiety,
b
[CoL1(H2O)3]
150–225, 346–589, >589
b
CoO
b
b
[NiL1(H2O)3]
154–216, 337–600, >600
14.57(14.78), 68.78(69.15), 20.67(20.44)
225 a, 430 b, 546
133 a, 250 a, 427
À3H2O(coord), loss of organic
moiety,
NiO
[CuL1(H2O)3]Á2H2O 52–120, 147–276, 367–640,
8.54(8.86), 13.06(13.29), 61.93(62.19),
20.37(19.58)
4.36(4.61), 13.72(13.84), 64.08(64.77),
21.11(20.86)
,
À2H2O(lattice), À3H2O(coord),
loss of organic moiety, CuO
ÀH2O(lattice), À3H2O(coord),
loss of organic moiety, ZnO
À2H2O(lattice)
b
>640
576
[ZnL1(H2O)3]ÁH2O
80–120, 165–247, 355–602,
>602
78 a, 231 a, 466
,
b
b
605
b
[RuL1(H2O)3]Á2H2O 60–110, 180–276, >355
8.23(8.11), 11.98(12.16)
106 a, 188 a, 360
461 b, 605 b, 688
,
b
–
À3H2O(coord), unassigned
a
Endothermic.
Exothermic.
b

D. Arish, M. Sivasankaran Nair / Journal of Molecular Structure 983 (2010) 112–121
119
temperature ranges 150–225 and 154–216 °C respectively. This is
due to a loss of three coordinated water molecule. The DTA curves
of the complexes show endothermic peak in the range 220–225 °C
confirming the dehydration process. The second decomposition
steps of the complexes in the 346–589 and 337–600 °C range have
DTA peaks at 430 and 437 °C, respectively. It brings a weight loss of
68.85% (cal. 69.10%) and 68.78% (cal. 69.15%), which correlate with
the loss of coordinated organic ligand. Above this temperature, a
horizontal thermal curve has been observed due to formation of
metal oxide. The TG curves of the complexes CuL1Á5 H2O and
ZnL1Á4H2O show a similar sequence of three decomposition steps.
The first stage takes place in the 52–120 °C and 80–120 °C ranges
with an endothermic DTA peak at 133 and 78 °C respectively for
CuL1Á5 H2O and ZnL1Á4H2O complexes. The mass loss observed (Ta-
ble 4) in this step corresponds to dehydration of lattice water mol-
ecule. The second stage starts from 147 °C to 276 °C for CuL1Á5 H2O
and 165 to 247 for ZnL1Á4H2O complexes with the DTA peak at 250
and 231 °C respectively. The corresponding mass loss (Table 4) is
attributed to the decomposition of three coordinated water mole-
cule. The third stage starts from 367 °C to 640 °C for CuL1Á5 H2O
and 355 to 602 for ZnL1Á4H2O complexes with the DTA peak at
427 and 466 °C respectively. The corresponding mass loss is due
Fig. 5. TG–DTA curves of (a) [CoL(H2O)3]; (b) [RuL(H2O)3]ÁH2O; (c) [CuL1(H2O)3]Á2H2O and (d) ZnL1Á4H2O complexes.
Fig. 6. Proposed structure of the complexes.

120
D. Arish, M. Sivasankaran Nair / Journal of Molecular Structure 983 (2010) 112–121
to the decomposition of the organic ligand molecule and which is
in agreement with a calculated mass loss (Table 4). The final resi-
due is qualitatively proved to be anhydrous metal oxide. The TG
curves of the complexes RuLÁ4H2O and RuL1Á5H2O show a weight
loss 4.07% (cal. 4.15%) and 8.23% (cal. 8.11%) in the temperature
ranges 60–98 °C and 60–110 °C with an endothermic DTA peak at
102 and 106 °C respectively, corresponding to a loss of lattice
water molecule. The second stage starts from 153 °C to 266 °C for
RuLÁ4H2O and 180 °C to 276 °C for RuL1Á5H2O complexes with
the DTA peak at 197 °C and 188 °C respectively. The corresponding
mass loss (Table 4) can be attributed to the decomposition of three
coordinated water molecules. Above this temperature, an unas-
signed mass loss was observed in both ruthenium complexes. This
step is accompanied by exothermic and endothermic peaks (Table
4). The representative TG–DTA curves of CoLÁ3H2O, RuLÁ4H2O,
CuL1Á5H2O and ZnL1Á4H2O complexes are shown in Fig. 5a–d.
Based on the above studies, the proposed structure of the metal
complexes is shown in Fig. 6.
Fig. 8a–d. Taking advantage of metal–ligand coordination interac-
tions, chemists have produced some interesting nano structured
complexes [42], which can be demonstrated by SEM or TEM micro-
graphs. Among the complexes, the [CuL1(H2O)]Á2H2O complex dis-
play very good surface morphology with existence of nano rod
structure. From the SEM image (Fig. 8b), it is observed that grains
are well resolved and circular shape are uniformly distributed in
the [CoL(H2O)3] complex. Moreover, the average grain size found
from SEM shows that the complex is polycrystalline with nano
sized grains. The SEM image of [CoL1(H2O)3] and [RuL1(H2O)]Á2H2O
complexes show irregularly shaped agglomerated particles of sub-
micron size. All other complexes show irregularly broken stone like
surface morphology and the presences of small grains are in micro
meter range.
4. Conclusion
Two new Schiff base ligands, cumi-gg(L) and pcb-gg(L1) and
their Co(II), Ni(II), Cu(II), Zn(II) and Ru(II) complexes were prepared
and characterized using various spectral techniques. The results
indicate that the complexes are octahedral, with formula
[ML(H2O)3]ÁxH2O (L = cumi-gg; x = 0 for M = Co(II), Ni(II), Cu(II)
and Zn(II); x = 1 for Ru(II) and L = pcb-gg; x = 0 for M = Co(II) and
Ni(II); x = 1 for Zn(II); x = 2 for Cu(II) and Ru(II)). The NMR and IR
spectra show that the ligands coordinate with metal ion through
azomethine nitrogen, deprotonated peptide nitrogen and carboxy-
lato oxygen atoms. All the complexes except Zn(II) display their re-
dox behavior. The thermal behavior of these chelates shows that
the hydrated complexes loss water of hydration in first step fol-
lowed by the loss of coordinated water molecules in the second
step. Decomposition of ligand molecules takes place in the subse-
quent steps. Interestingly, [CoL1(H2O)3] complex exhibit nano rod
structure.
3.8. Powder XRD and SEM
Powder XRD pattern of the Schiff base complexes were recorded
over the 2h = 0–80 range and [CoL(H2O)3], [CoL1(H2O)3] and [CuL1(-
H2O)]Á2H2O are shown in Fig. 7a–c. The [CoL(H2O)3], [CoL1(H2O)3]
and [CuL1(H2O)]Á2H2O complexes display sharp crystalline peaks
indicating their crystalline nature, whereas other complexes do
not exhibit well-defined crystalline peak due to their amorphous
nature. The average crystallite sizes of the complexes dXRD were
calculated using Scherre’s formula [41]. The [CoL(H2O)3], [CoL1(-
H2O)3] and [CuL1(H2O)]Á2H2O complexes have an average crystal-
lite size of 48, 61 and 42 nm, respectively, suggesting that the
complexes are in nanocrystalline phase.
The SEM micrographs of the [CoL1(H2O)3], [CoL(H2O)3], [CuL1
(H2O)]Á2H2O and [RuL1(H2O)]Á2H2O complexes are shown in
Fig. 7. Powder XRD pattern of (a) [CoL(H2O)3]; (b) [CoL1(H2O)3] and (c) [CuL1(H2O)3]Á2H2O Complexes.

D. Arish, M. Sivasankaran Nair / Journal of Molecular Structure 983 (2010) 112–121
121
Fig. 8. SEM images of (a) [CoL1(H2O)3]; (b) [CoL(H2O)3]; (c) [CuL1(H2O)]Á2H2O and (d) [RuL1(H2O)]Á2H2O complexes.
[20] Y. Zou, W. Liu, C. Lu, L. Wen, Q. Meng, Inorg. Chem., Commun. 7 (2004)
985.
Acknowledgment
[21] Y. Zou, W. Liu, J. Xie, C. Nia, Z. Nia, Y. Li, Q. Meng, Y. Yao, J. Coord. Chem. 57
(2004) 381.
One of the authors (D.A) is grateful to National Testing Service-
India, CIIL, Mysore for providing the fellowship.
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[25] R.S. Josephus, M.S. Nair, Arabian. J. Chem., in press, doi:10.1016/
j.arabjc.2010.05.001.
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