Spectrophotometric study on the adduct formation of nickel (II)-di(2,4-dimethylphenyl)carbazonate with heterocyclic nitrogen bases

Article abstract of DOI:10.1016/S1386-1425(01)00424-3

The study of the adduct formation of Ni(II)di(2,4-dimethylphenyl)cabazonate has been undertaken by synthesising and characterising it by magnetic susceptibility, IR and ¹H-NMR spectral measurements. The Ni(II) chelate forms adducts with heterocyclic nitrogen bases, spectrophotometeric method has been employed for the study of the adduct formation in a monophase chloroform. Both bidentate and unsaturated monodenate heteronuclear nitrogen bases form hexa-coordinated adducts with 1:1 stoichiomety (metal chelate, base). However, the saturated nitrogen bases form penta-coordinated adducts with 1:1 stoichiometry. The results are discussed in terms of basicity and steric factors of the bases.

Full text of DOI:10.1016/S1386-1425(01)00424-3

Spectrochimica Acta Part A 57 (2001) 2721–2727
www.elsevier.com/locate/saa
Spectrophotometric study on the adduct formation of nickel
(II)-di(2,4-dimethylphenyl)carbazonate with heterocyclic
nitrogen bases
A.H.M. Siddalingaiah *, A.F. Dodamani, Sunil G. Naik
Department of Chemistry, Karnatak Uni6ersity, Dharwad 580 003, India
Received 8 November 2000; accepted 12 January 2001
Abstract
The study of the adduct formation of Ni(II)di(2,4-dimethylphenyl)cabazonate has been undertaken by synthesising
1
and characterising it by magnetic susceptibility, IR and H-NMR spectral measurements. The Ni(II) chelate forms
adducts with heterocyclic nitrogen bases, spectrophotometeric method has been employed for the study of the adduct
formation in a monophase chloroform. Both bidentate and unsaturated monodenate heteronuclear nitrogen bases
form hexa-coordinated adducts with 1:1 stoichiomety (metal chelate, base). However, the saturated nitrogen bases
form penta-coordinated adducts with 1:1 stoichiometry. The results are discussed in terms of basicity and steric
factors of the bases. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Adduct formation; Heterocyclic nitrogen bases; Basicity and steric factors
reagent [3,4] much earlier than its sulphur ana-
logue, dithizone, it has received considerably less
attention as a ligand for metal complexes [5,6].
Comprehensive studies of Ni(II) dithiozonates
and their pyridine adducts have revealed the ana-
lytical importance of adduct formation in the
extraction of trace amounts of metals [7,8]. The
associated spectral changes can be employed to
determine adduct formation constants and to
confirm the structure of the pyridine adduct [9].
Hence, in this work, we have undertaken the
synthesis, characterisation and have studied ad-
duct formation of nickel (II)-di(2,4-dimethyl-
phenyl)carbazonate [Ni(2,4DMPC)2], as a contin-
uation of our earlier research [10–12].
1. Introduction
Diphenylcarbazone (DPC) [1], a keto com-
pound can exist in enolic form when dissolved in
an organic solvent and react with various metal
ions to form intense coloured metal complexes.
Therefore it has been used in the determination of
Mn1, Cu2 and fatty acids [2] in blood serum etc.
Though, it was introduced as an analytical
* Corresponding author. Tel.: +91-747-12115; fax: +91-
836-747884.
E-mail address: karuni@bgl.vsnl.net.in (A.H.M. Siddalinga-
iah).
1386-1425/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S1386-1425(01)00424-3

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A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 57 (2001) 2721–2727
2. Experimental
2.1. Apparatus
2.3. Preparation of D2,4DMPC
It was synthesised by a method described earlier
[14,15]. Di(2,4-dimethylphenyl) carbazide was first
prepared by heating mixture of 2,4-
Absorbances were measured on a Hitachi 150-
20 Uv-Vis. Spectrophotometer. Elemental analysis
was carried out on Perkin–Elmer 240 CHN
a
dimethylphenyl hydrazine and urea (2:1) at 155–
160°C for about 3 h, the crude carbazide so
obtained was crystallised from alcohol. About 1 g
of the carbazide in a mixture of 60 ml glacial
acetic acid was oxidised with 20 ml of 0.06 M
potassium persulfate (K2S2O8) adding dropwise
with vigorous stirring for about 30 min. The
resulting carbazone was extracted with ether,
washed several times with water, evaporated,
dried and purified by column chromatography
using silica gel (60–120 mesh) column. A mixture
of Me2CO and CHCl3 (1:4) was used as an eluent
(yield 42%; m.p. 110°C).
1
analyser, IR and H-NMR spectra were recorded
on Perkin–Elmer 157 and VXR 300S Varian
spectrometers, respectively. The magnetic moment
of the nickel complex was determined by the
Gouy method. The metal content was estimated
by EDTA titration [13].
2.2. Chemicals and reagents
Pyridine (Fisher), picolines (Eastman), lutidi-
nes, collidine and ethylenedimmine (BDH) were
dried over KOH and redistilled. Pyrrolidine, pipe-
ridine and morpholine (BDH) and hexam-
ethylene-imine (Sigma) were purified by refluxing
over BaO for 18–24 h followed by fractional
distillation. 2,2%bipyridyl (Eastman), 1,10-phenan-
throline (G.F. Smith), 2,9-neocuproine (BDH),
CHCl3 (Merck) and nickel chloride (Fisher AR
grade) were used as supplied.
2.4. Nickel (II)-D2,4DMPC complex
A solution of NiCl2 (1 g) in an acetate buffer
(pH 6.2) was mixed with 0.01 M EtOH solution
of 2,4DMPC at room temperature (Fig. 1). The
mixture was stirred and the resulting precipitate
was collected by suction and was washed several
times with H2O. The complex was dried over
P4O10 in vacuo at room temperature and then
purified by Soxhlet method [16], using (1:1)
Et2O:petroleum ether as solvent. The extract con-
tained impurities and failed to give the character-
istic colour of the adduct with nitrogen bases. The
pure complex was obtained as shining crystalline
power in the Soxhlet tube (yield 70%; m.p.
248°C).
2.5. Measurement of absorbances
CHCl3 solutions (1 cm3 in each case) of the
nickel complexes were pipetted into standard flask
(10 cm3) containing different amounts of nitrogen
bases (dissolved in CHCl3). Each of the mixtures
in the flask were diluted to the mark with solvent.
The absorption spectra were measured in the visi-
ble region at 400–700 nm with a 10 mm optical
path length, using CHCl3 as a reference. The
absorption at 640 nm was used for analysis. A
typical spectrum of the Ni(D2,4DMPC)2-
2,2%bipyridyl adduct is as shown in Fig. 2.
Fig. 1. (a) Structure of D2,4DMPC, (b) structure of
Ni(D2,4DMPC)2.

A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 57 (2001) 2721–2727
2723
Fig. 2. Absorption spectra of Ni(D2,4DMPC)2+2,2%bipyiridyl mixture in CHCl3 (10 cm3). [Ni(D2,4DMPC)2]=1.478×10−5 M;
[2,2%-bipyridyl]×10−6 M (a) 0.00; (b) 1.36; (c) 2.71; (d) 4.07; (e) 5.42; (f) 6.78; (g) 9.50; (h) 10.85; (i) 12.20; (j) 14.92; (k) 17.63; (l)
21.70.
Table 1
Physical and analytical data for D2,4DMPC and [Ni(D2,4DMPC)2]
Compound
M.P. (°C)
Found (calculated)%
meff (BM)
C
H
N
M
D2,4DMPCa
110
210
68.63
(68.91)
62.90
6.68
(6.76)
5.83
18.70
(18.92)
17.20
–
C17H20N4O
[Ni(D2,4DMPC)2]b
Ni(C34H38N8O2)
9.00
(9.04)
2.28
(62.88)
(5.90)
(17.26)
a D2,4DMPC, di(2,4-dimethylphenyl)carbazone.
b [Ni(D2,4DMPC)2], Ni (II)-di(2,4-dimethylphenyl) carbazonate.

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A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 57 (2001) 2721–2727
Table 2
IR and 1H-NMR spectral data
a
Compound
D2,4DMPC
g(NꢁH)
g(CꢀO)
g(NꢀN)
g(CꢀN)
g
(CꢀC)ar
g(CꢁO)
1H-NMR (d) ppm
3400/3283
3160, 3085
1720
1593
–
1468
–
6.21 (br, ꢁNHꢁAr)
7.9 (br, ꢁNHꢁamide)
6.7–7.6 (m, ArꢁH)
2.2, 2.4, 2.5 (S, ꢁCH3)
[Ni(D2,4DMPC)2]
3307
–
1590
1560
1458
1056
1180
1201
–
a Intermolecular/intramolecular.
3. Results and discussion
3400 cm−1 attributed to the intermolecular
bonded g(NꢁH) vibration. Bands at 3283, 3160 and
3085 cm−1 have been attributed to the in-
tramolecular bonded g(NꢁH) vibration [1]. The
band at 1720 cm−1 is assigned to CꢀO stretching
vibration and a band at 1590 cm−1 to NꢀN
stretching vibrations. The disappearance of the
g(CꢀO) stretching a band at 1720 cm−1 in the
complex indicates that the oxygen atom of the
ligand is involved in coordination to the metal
through the enolic tautomer. This fact was further
The physical and analytical data of the ligand
and the metal complex are given in Table 1 and
confirm that the complex contains 1:2 metal–lig-
and stoichiometry. The complex is air stable, non-
hygroscopic and soluble in non-polar solvents.
The sub-normal magnetic moment (2.28 BM) for
the Ni (II) chelate requires explanation, since the
spin-only value (2.83 BM) is expected for tetrahe-
dral or octahedral geometries. The result is at-
tributed to the mixed stereochemistry around Ni
(II) [17,18]. As Ni (II) (D2,4DMPC)2 gives charge
transfer transitions with high molar absorptivity,
it is often difficult to determine the mixed stereo-
chemistry around Ni (II) ion on the basis of
electronic spectral data, as explained earlier [8].
Furthermore, a large magnetic moment is associ-
ated with tetrahedral geometry and, in solution
bidentate and unsaturated monodentate bases
form hexacoordinated adduct with 1:1 and 1:2
metal–ligand stoichiometries respectively, which
exclude the possibility of tetrahedral and octahe-
dral geometries. Hence, it is assumed that the
chelate undergoes distortion in chloroform to
such an extent that it almost conforms to square
planar structure. This paves the way for the for-
mation of penta- and hexa-coordinated adduct
[19–21].
Table 3
Formation constants of [Ni(D2,4DMPC)2] adduct system in
chloroform
Base
PKa
Slope (n)a
band
Pyridine
5.20
–
ID
2-Picoline
3-Picoline
4-Picoline
5.90
5.86
6.08
6.72
6.52
7.48
–
2
–
–
2
–
2
–
–
1
1
1
1
2.65
ID
ID
3.00
ID
3.10
ID
2,4-Lutidine
3,4-Lutidine
2,4,Collidine
3-Cyanopyridine
4-Cyanopyridine
Pyrrolidine
Piperidine
Hexamethyl-imine
Morpholine
2,2%-Bipyridyl
1,10-Phenanthroline
2,9-Neocuproine
Ethylenediamine
–
ID
11.27
11.00
11.07
8.35
4.40
4.95
5.85
6.84
3.15
2.75
2.25
1.75
5.30
5.26
5.15
5.20
1b
1b
1b
1b
3.1. IR spectra
The IR spectra of the ligand and complex were
recorded in the 4000–400 cm−1 range in KBr
pellets (Table 2). The ligand exhibited a band at
a Number of base molecules per chelate.
b Value obtained from mole-ratio method. ID, instanta-
neously decolourised.

A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 57 (2001) 2721–2727
2725
Fig. 3. Sigmoidal plots for the adducts of Ni(D2,4DPMC)2 monodentate bases in chloroform.
tions in chloroform change to pink upon adduct
formation. Two isosbestic points in the visible
region occur at around 574 and 476 nm for the
adduct system. Measurements at 640 nm were
plotted as a function of −log [B] in order to
generate sigmoidal curves as shown in Fig. 3. The
data obtained from the extrapolation of these
curves are used in the calculation of stability
constant log band values using the equation
confirmed by the appearance of a band at 1560
cm−1 due to g(CꢀN) stretching. Based on analytical
and spectral data, the structures of ligand and
complex are assigned as shown in Fig. 2.
3.2. Adduct formation
The absorption spectra were measured in the
visible region at 400–700 nm using chloroform
(10−3 M) as the reference (Table 3). The chloro-
form solution of [Ni(D2,4DMPC)2] (in the ab-
sence of a heterocyclic nitrogen base) has two
absorption bands in the visible region at 640 nm,
m=4.5×104 lmol−1 cm−1) and a shoulder at 468
nm, m=3.81×104 lmol−1 cm−1). The spectrum
of [Ni(D2,4DMPC)2] undergoes an intense change
on addition of a chloroform solution of the hete-
rocyclic bases and the deep violet chelate solu-
Ach−A
A−Aad
log iand= −n log [B]+log
(1)
Here n is the number of base adducts B at-
tached to the chelate, Ach and Aad are respective
absorbances due to chelates and adducts and A is
the absorbance due to the chelate adduct equi-
librium mixture. The log band values for
[Ni(D2,4DMPC)2] with saturated bases such as
pyrrolidine, piperidine, hexamethylene-imine and

2726
A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 57 (2001) 2721–2727
Fig. 4. Linear plots for the adducts of Ni(D2,4DPMC)2 monodentate bases in chloroform.
Fig. 5. Mole-ratio plots for the adducts Ni(D2,4DPMC)2 bidentate bases in chloroform.

A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 57 (2001) 2721–2727
2727
The considerable increase in absorbance due to
adduct formation constitutes the bases for the
extraction of nickel with chloroform and hence,
the ligand D2,4DMPC can be used as analytical
reagent for this purpose.
morpholine form pentacoordinate adducts of
1:1 stoichiometry. The stability of the adducts
decreases from 5-membered pyrrolidine to the
7-membered hexamethylene-imine ring membered
hexamethylene-imine ring (pyrrolidine\pipe-
ridine\hexamethylene-imine\morpholine) indi-
cating the influence of ring size on adduct
formation. The formation of a less stable adduct
with morpholine may be due to the decreased
basicity of the nitrogen atom in the morpholine
ring [22].
The monodentate pyridine bases form 1:1
penta-coordinated adduct with [Ni(D2,4DMPC)2]
as shown by the unit slope for plots of log [(Ach−
A)/A−Aad)] versus −log [B], (Fig. 4). The stabil-
ity order for these adducts follows the expected
steric hindrance and basicity of the adducting
bases: 2-picolineB2,4-lutidineB2,4,6-collidineB
pyridineB3-picolineB4-picoline. This follows
the expected resonance and substituent effects or-
der for the bases [23,24].
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phenanthroline, 2,9-neocuprine and ethylenedi-
amine, in addition to the unit slope found from
Eq. (1), the mole ratio method was also used to
confirm the chelate base ratio. The mole ratio
method shows that the stoichiometry for the
chelate-bidentate base is 1:1, accounting for the
six coordination sites around the nickel atom,
forming the octahedral structure. The mole ratio
plot for the Ni(D2,4DMPC)2-2,2%bipyridyl and
1,10-phenanthroline adduct systems is shown in
Fig. 5. Here, the formation of adducts might be
due to rearrangement of the chelate rings in order
to provide a cis disposition for the bidentate
bases. The cis adduct thus formed was of almost
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mation with bidentate bases is not much influ-
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