Spectral studies on cobalt(II), nickel(II) and copper(II) complexes of naphthaldehyde substituted aroylhydrazones

Article abstract of DOI:10.1016/j.saa.2005.08.014

A series of new coordination complexes of cobalt(II), nickel(II) and copper(II) with two new aroylhydrazones, 2-hydroxy-1-naphthaldehyde isonicotinoylhydrazone (H₂L¹) and 2-hydroxy-1-naphthaldehyde-2-thenoyl-hydrazone (H₂L²) have been synthesized and characterized by elemental analysis, conductance measurements, magnetic susceptibility measurements, ¹H NMR spectroscopy, IR spectroscopy, electronic spectroscopy, EPR spectroscopy and thermal analysis. IR spectra suggests ligands acts as a tridentate dibasic donor coordinating through the deprotonated naphtholic oxygen atom, azomethine nitrogen atom and enolic oxygen atom. EPR and ligand field spectra suggests octahedral geometry for Co(II) and Ni(II) complexes and a square planar geometry for Cu(II) complexes.

Full text of DOI:10.1016/j.saa.2005.08.014

Spectrochimica Acta Part A 64 (2006) 853–858
Spectral studies on cobalt(II), nickel(II) and copper(II) complexes of
naphthaldehyde substituted aroylhydrazones
Pramod Kumar Singh , Deo Nandan Kumarb
a,∗
a
Department of Chemistry, Kirori Mal College, University of Delhi, Delhi 110007, India
b
Department of Chemistry, University of Delhi, Delhi 110007, India
Received 15 May 2005; received in revised form 31 July 2005; accepted 19 August 2005
Abstract
A series of new coordination complexes of cobalt(II), nickel(II) and copper(II) with two new aroylhydrazones, 2-hydroxy-1-naphthaldehyde
1
2
isonicotinoylhydrazone (H
2
L ) and 2-hydroxy-1-naphthaldehyde-2-thenoyl-hydrazone (H
2
L ) have been synthesized and characterized by elemen-
1
tal analysis, conductance measurements, magnetic susceptibility measurements, H NMR spectroscopy, IR spectroscopy, electronic spectroscopy,
EPR spectroscopy and thermal analysis. IR spectra suggests ligands acts as a tridentate dibasic donor coordinating through the deprotonated
naphtholic oxygen atom, azomethine nitrogen atom and enolic oxygen atom. EPR and ligand field spectra suggests octahedral geometry for Co(II)
and Ni(II) complexes and a square planar geometry for Cu(II) complexes.
©
2006 Elsevier B.V. All rights reserved.
Keywords: Aroylhydrazones; Cobalt(II); Nickel(II); Copper(II); EPR spectra; IR spectra; Ligand field spectra
1
. Introduction
The possible mode of the complexes is discussed on the basis
of various spectroscopic methods.
The coordination chemistry of substituted hydrazones has
received much impetus by the remarkable anticancer, amoe-
bicidal, antibacterial, antimicrobial and antileukaemic activi-
ties exhibited by these compounds which can be related to
their metal complexing abilities. Aroylhydrazone possess strong
pharmacologial properties and may inhibit many enzymatic
reactions catalysed by transition metals. The chemical and phar-
macological properties of aroylhydrazone have been extensively
investigated owing to their potential applications as antineoplas-
tic, antiviral, antiinflammatory [1–5] and antitumor agents [6].
Hydrazides and hydrazones have interesting ligation properties
due to presence of several coordination sites.
2
. Experimental
All the chemicals and metal salts used in the synthe-
sis were of reagent grade and used without further purifi-
cation. The solvents were dried before use by conventional
methods.
2.1. Preparation of ligands
1
The ligand HL was prepared as follows: a solution of ison-
3
icotinoylhydrazine (0.05 mol) in anhydrous ethanol (50 cm )
were added dropwise to the ethanolic solution (50 cm ) of
In continuation of earlier work [7,8] on the metal com-
plexes of hydrazones, this paper reports the synthesis and
characterization of cobalt(II), nickel(II) and copper(II) com-
3
2-hydroxy-1-naphthaldehyde (0.05 mol) with stirring and the
mixture was heated under reflux for 4 h. The solution was con-
centrated to half of its initial volume and cooled to room temper-
ature. The white precipitate was separated by filtration, washed
with hot ethanol and dried in vacuo. The yield was 75% and
plexes of 2-hydroxy-1-naphthaldeyde isonicotinoylhydrazone
1
(
H2hnih = H2L ) and 2-hydroxy-1-naphthaldehyde-2-thenoylh-
2
1
ydrazone (H2hnth = H2L ) (Fig. 1) of the types [ML ]·nH2O
2
(
n = 2) and [ML ]·nH2O (n = 1−2).
◦
mp = 180–182 C.
2
The preparation method for the ligand H2L was similar to
1
2
∗
2 2
that of the ligand H L and pale yellow precipitate of H L was
Corresponding author. Tel.: +91 98111 41002; fax: +91 27666423.
E-mail address: deonandan2002@rediffmail.com (D.N. Kumar).
obtained by adding ethanolic solution of 2-thenoylhydrazine to
1
386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.08.014

8
54
P.K. Singh, D.N. Kumar / Spectrochimica Acta Part A 64 (2006) 853–858
Fig. 1. Structures of the ligands.
the ethanolic solution of 2-hydroxy-1-naphthaldhyde. The yield
◦
was 70% and mp = 175–197 C.
2
.2. Synthesis of complexes
The complexes were prepared by adding metal acetate
3
(
0.5 mo1) [metal = Co(II), Ni(II), and Cu(II)] in ethanol (10 cm )
1
dropwise to the hot solution of respective ligands (H2L and
2
3
H2L ) in ethanol (10 cm ). The mixture was maintained under
reflux for 3 h, then cooled, filtered, washed with ethanol and
dried in vacuo. While preparing the cobalt complex, a drop of
glacial acetic acid was added to the cobalt acetate solution to
prevent its hydrolysis. The purity of complexes were checked
by TLC and elemental analyses.
2
.3. Elemental analysis and physical measurements
Metal contents were estimated using Perkin-Elmer 2380
atomic absorption spectrophotometer. Elemental analyses (C,
H and N) were carried out microanalytically at IIT, New Delhi
(
India). The IR spectra were recorded on Perkin-Elmer FT-IR
−
1
spectrophotometer as KBr discs in the 4000–200 cm region.
1
H NMR spectra were obtained on Varian FT-80A NMR spec-
trometer using DMSO-d as a solvent and TMS as internal
6
standard. Room temperature magnetic moment were measured
using a vibrating sample magnetometer PAR 155 at 500 G with
nickel as standard. Molar conductances were measured in DMF
−3
(
10 M) with digital conductivity meter model 304. Electronic
spectra were recorded in DMF on a Beckman DU-2 spectropho-
tomer. X-band EPR spectra were recorded on JEOL JES-3XG
ESR spectrometer. Thermal behaviour was monitored on 8150
◦
−1
.
thermoanalyser at the heating rate of 10 min
. Results and discussion
The analytical data and physical properties of the ligands and
3
coordination compounds are listed in Table 1. The results from
Table 1 show that the ligands coordinate to the metal ion in a 1:1
molar ratio. The ligands are soluble in hot ethanol and strong
polar solvents such as in DMF and DMSO. All compounds are

P.K. Singh, D.N. Kumar / Spectrochimica Acta Part A 64 (2006) 853–858
855
Table 2
IR spectral data of ν(OH), ν(NH), ν(C O), ν(C N), δ(N H), ν(N N), ν(C N) + δ(N H), ν(N H) + δ(C O), ν(M O) and ν(M N) in cm
−
1
Compound
ν(OH)
ν(NH)
ν(C O)
␯(C N)
δ(N H)
ν(N N)
ν(C N) + δ(N H)
ν(N H) + δ(C O)
ν(M O)
ν(M N)
H2L1
1
3495
3160
1650
1550
1535
1525
1535
1580
1530
1520
1536
1490
960
1000
995
1000
965
1015
1025
1020
[
[
[
CoL ]·2H2O
3350a
1630
1635
1625
1335
1340
1345
470
480
465
345
360
365
1
a
NiL ]·2H2O
3360
1
3385a
3510
CuL ]·2H2O
2
H2L
3280
1640
1520
2
3385a
[
[
[
CoL ]·H2O
1635
1630
1630
1330
1335
1345
480
485
465
350
365
345
2
a
NiL ]·2H2O
3380
3390a
2
CuL ]·2H2O
a
Due to water molecule.
stable in air. The melting points of the complexes are higher than
that of the ligands revealing that the complexes are much more
stable than the ligands. Due to insolubility of the complexes
in benzene/nitrobenzene, the molecular weights could not be
obtained by cryoscopy. The molar conductance values (Table 1)
3
.2. 1H NMR spectra
The 1H NMR spectra of the ligands (H2L1 and H2L2)
recorded in DMSO-d . The down field shift of the OH pro-
ton in the ligand which resonates at 10.4 ppm in its H NMR
spectrum indicates that the OH proton in ligands are proba-
bly involved in the formation of strong intramolecular hydrogen
bonding (Fig. 1).
6
1
−
1
2
−1
of the complexes lies in the range 18.3–25.2 ꢀ cm mol (at
◦
1
5 C) which indicates that the complexes are of non-electrolytic
nature [9].
The NMR spectrum of the ligands exhibits NH proton at
1
1.16 ppm, a >CH proton at 4.65 ppm, naphthalene ring pro-
3
.1. Infrared spectra
tons at 6.2–8.68 ppm (multiplets), isonicotinyl protons at 9.00
and 8.10 ppm (each as a doublet) and theonyl protons at 7.75
and 8.79 ppm (each as a doublet). The H NMR spectra of the
complexes cannot be obtained due to interference in their para-
magnetic properties.
The IR spectra (Table 2) of the ligands show characteris-
1
tic absorption bands at 3490–3515, 3150–3280, 1630–1660,
−
1
1
545–1590, 1485–1530 and 958–969 cm
due to ν(O H),
ν(N H), ν(C O), ν(C N), δ(N H) and ν(N N), respectively.
The IR spectra (Fig. 2(A)–(F)) of the complexes reveal signifi-
cant changes compared to those of the ligands. The absorption
bands at 3450–3490 cm for ν(O H) in the free ligand dis-
appeared on complexation indicating coordination through a
deprotonatedoxygen. Theabsorptionbandattributedto ν(N H),
ν(C O) and δ(N H) disappeared in the complexes and two new
3.3. Ligand field spectra and magnetic moments
−
1
The ligand field spectra (Table 3) of all the complexes were
recorded in DMF at room temperature.
The electronic spectra of Co(II) complexes displayed three
−
1
−1
bands at 7900–8150 cm (ν1), 16 300–16 400 cm (ν2) and
1
−
bands due to conjugate system ν(>C N N C<) and ν(C O )
−
1
4
4
9 600–20 150 cm
(ν3) corresponding to T1 g (F) → T2 g
−
1
[
8] appeared in the regions 1620–1635 and 1330–1345 cm
,
4
4
4 4
(
F), T1 g (F) → A2 g and T1 g → T1 g (P) transitions, respec-
tively, characteristic of octahedral geometry of complexes
11,12].
The values of transition ratio ν2/ν1 and β lies in the range
respectively. The band for ν(C N) undergoes a bathochromic
shift of 15–25 cm (in H2L ) and 50–60 cm (in H2L ) and
ν(N N) band exhibited a hypsochronic shift of 35–45 cm (in
−
1
1
−1
2
[
−
1
1
−1
2
H2L ) and 50–60 cm (in H2L ) which indicate that the metal
ions form neutral coordination compounds with the ligand in the
enol form through the azomethine nitrogen and amide oxygen
negative ion [10]. A shift of ν(C N) band to a lower frequency
is due to the conjugation of the p-orbital on the double bond with
the d-orbital on metal ion with reduction of the force constant.
A shift of ν(N N) band to a higher frequency is attributed to the
electron attracting inductive effect when forming the conjugated
system [8].
The characteristic absorption bands of the ligands and com-
plexes attributed to ␯(C C) and ␯(C H) of the naphthalene ring
appear at 1565–1590 and 730–745 cm regions, respectively.
The new absorption band at 3350–3410 cm in all the com-
plexes, assignable to hydroxyl stretching vibration of the crystal
water involved in the complexes. In the far—IR region two new
2
.06−2.09 and 0.87, respectively, providing further evidences
for octahedral geometry for cobalt(II) complexes. The room
temperature magnetic moment values of Co(II) complexes are
within the range 4.28−4.99 BM suggest spin free octahedral
geometry [12,13].
The nickel(II) complexes displayed three bands 8880–
− −1
1
9000 cm (ν1), 14 850–14 950 cm (ν2) and 25 000–25 100
Table 3
Ligand field spectral data (cm 1) of complexes
−
Compound
ν1
ν2
ν3
ν2/ν1
β
−
1
1
[
[
CoL ]·2H2O
7900
16350
14870
19000
16380
14900
20000
19700
25050
2.070
1.673
0.87
0.90
−
1
1
NiL ]·2H2O
8890
14500
7950
8900
15600
1
[CuL ]·2H2O
2
[
CoL ]·H2O
20140
25000
2.060
1.674
0.88
0.91
2
−
1
[NiL ]·2H2O
bands around 465–485 and 340–365 cm in the complexes can
be assigned to ν(M O) and ν(M N), respectively.
2
[
CuL ]·2H2O

8
56
P.K. Singh, D.N. Kumar / Spectrochimica Acta Part A 64 (2006) 853–858
1
1
1
2
2
Fig. 2. IR spectra of: (A) [CoL ]·2H2O complex; (B) [NiL ]·2H2O complex; (C) [CuL ]·2H2O complex; (D) [CoL ]·H2O complex; (E) [NiL ]·2H2O complex; (F)
2
[
CuL ]·2H2O complex.
−
1
3
3
3
3
2
2
cm (ν3) attributable to A2 g → T2 g (F), A2 g → T1 g (F)
B1 g → Eg of a square planar structure [11]. The copper(II)
3
3
and A2 g → T1 g (P), transitions, respectively, suggestive of
octahedral geometry [11,14]. The value of transition ratio ν2/ν1
and β lies in the range 1.60–1.70 and 0.90 respectively pro-
viding further evidences for octahedral geometry for nickel(II)
complexes. The β values for the complexes are lower than the
free ion value, thereby indicating orbital overlap and delocali-
sation of d-orbitals. The β-values obtained are less than unity
suggestive considerable amount of covalent character of the
metal–ligand bonds. Nickel(II) complexes are paramagnetic and
the room temperature magnetic movement value 2.98−3.20 BM
which is well within the range of octahedral nickel(II) species
15,16].
The electronic spectra of copper(II) complexes shows absorp-
tion band in the ranges 14 000–15 700 and 18 910–20 150 cm
assignable respectively, to transitions B1 g → B2 g and
complexes are paramagnetic and the room temperature mag-
netic moments values are indicative of one unpaired electron
per Cu(II) ion, µeff = 1.80–2.10 BM These values are close to or
slightly higher than the spin−only value, indicates absence of
any magnetic exchange interactions between copper(II) ions.
3.4. EPR spectra
EPR spectra (Fig. 3) of copper(II) complexes recorded in
polycrystalline state at room temperature (Table 4) also provides
information about the square planar geometry of the copper(II)
complexes. The spectra are typical for axial type complexes,
from which gꢀ, g⊥, ꢁgꢂ and Aꢀ have been calculated. The order-
ing of g values gꢀ > g⊥ > 2.0023 observed for copper(II) com-
plexes indicates that the unpaired electron most likely resides
[
−
1
,
2
2

P.K. Singh, D.N. Kumar / Spectrochimica Acta Part A 64 (2006) 853–858
857
1
2
Fig. 4. Proposed structure for [ML ]·nH2O and [ML ]·nH2O complexes, where
1
H2L = H2hnih; M = Co(II) (n = 2), Ni(II) (n = 2), Cu(II) (n = 2); R =
and H2L = H2hnth; M = Co(II) (n = 1), and Ni(II) (n = 2), and Cu(II) (n = 2);
2
R =
.
3.5. Thermal analysis
TG and DTA studies were carried out on the ligands and
◦
its complexes in the temperature range 20–900 C. The thermal
analyses show that there are two endothermic peaks in the DTA
◦
1
curve of the ligands. The first appeared at 180 C (in H2L )
◦
2
and at ꢃ190 C (in H2L ) are melting points of the ligands,
because no loss of weight was observed in the TG curve. The
◦
second peak appeared above 390 C where the weight loss on the
corresponding TG curve indicates decomposition of the ligands.
The decomposition is complete at about 495 C.
1
2
Fig. 3. EPR spectra of: (A) [CuL ]·2H2O complex; (B) [CuL ]·2H2O complex.
◦
The thermal decomposition curves of the complexes are dif-
ferent from that of the ligands. There is no endothermic peaks,
only a series of exothermic ones in the DTA curves indicat-
ing no melting points for these complexes. The first step in the
in their d
2
2
orbital [17] which is consistent with proposed
x − y
2
planar stereochemistry [18,19] and B1 g ground state [20]. gꢀ
is a moderately sensitive function for indicating covalency and
gꢀ > 2.3 and gꢀ < 2.3 is characteristic of anionic and covalent
environments, respectively, in metal–ligand bonding. The fact
that the gꢀ values (Table 2) are less than 2.3 is an indication of
significant covalent bonding in copper(II) complexes [21–23].
In axial symmetry G (= gꢀ−2/g⊥−2), is a measure of the
exchange interaction between Cu(II) centres in polycrystalline
state [24]. Thevalue of G > 4 indicates negligible exchange inter-
action in solid complexes [18,25]. The G value in copper(II)
◦
decomposition sequence at 115–185 C corresponds to the loss
of water of crystallisation present in the complexes, which are
in agreement with the calculated values. The second step of
◦
decomposition of all the complexes starts from about 250 C
◦
and continues up to 650 C, except for copper(II) complexes for
which decomposition continues up to 850 C as shown by the
◦
horizontal plateau on the TG curves. A horizontal plateau on
the TG curves for all the complexes indicates the decomposi-
tion of the organic part of the chelate in the last step leaving
residues of metallic oxide at the final temperature. The final
weight of the residues correspond to the corresponding metal
oxides [26] as end-product. The decomposition temperatures of
the complexes are higher than that of the ligands (Table 1), indi-
cates that the thermal stability of the complexes are increased
due to the ligand coordinating with metal ions to form stable
ring.
We have not so far been successful to obtain crystals of the
complexes suitable for X-ray analysis. The above mentioned
results indicate that the ligands are enolised in solution and
chelated to the metal ions through the deprotonated naphtholic
oxygen atom, azomethine nitrogen atom and the enolic oxygen
atom.
complexes are less than 4 suggesting d
a small exchange coupling [19]. The fraction of unpaired elec-
tron density located on the copper ion i.e. the value of in-plane
2
2
ground state with
x − y
2
sigma bonding parameter α was estimated from the expression
[
21,22]
2
α = −Aꢀ/0.036 + (gꢀ − 2.0023) + 3/7(g⊥ − 2.0023) + 0.04
2
where Aꢀ is the parallel coupling constant. The value of α
(Table 2) indicates that the copper(II) complexes are fairly cova-
lent. The EPR spectra in liquid nitrogen temperature could not
provide any additional information.
Table 4
EPR spectral data for Cu(II) complexes
On the basis of above arguments, the proposed structure for
the complexes are shown in Fig. 4.
1
2
Parameters
[CuL ]·2H2O
[CuL ]·2H2O
gꢀ
2.290
2.112
2.18
194
2.86
0.61
2.295
2.114
2.18
192
2.85
0.60
g⊥
Acknowledgements
ꢁ
gꢂ
Aꢀ
The authors (PKS) acknowledge the help rendered by Head,
I.I.T. Delhi and Head, Department of Chemistry, University of
Delhi, Delhi for microanalyses, thermal and spectral studies of
G
2
α

8
58
P.K. Singh, D.N. Kumar / Spectrochimica Acta Part A 64 (2006) 853–858
the complexes. D.N.K. is thankful to CSIR, New Delhi for award
of Research Associateship.
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3 (1993) 17.
2
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[15] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 3rd ed.,
Wiley/Interscience, New York, 1972, p. 894.
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