A study of adduct formation of heterocyclic nitrogen bases with nickel(II) chelate of di(6-chloro-2-methylphenyl)carbazone.

Article abstract of DOI:10.1016/S1386-1425(00)00316-4

The study of the adduct formation of Ni(II) di(6-chloro,2-methylphenyl)carbazonate has been undertaken by synthesising and characterizing it by magnetic susceptibility, UV-VIS, IR and 1H-NMR spectral measurements. The distorted square planar Ni(II) chelate forms adducts with heterocyclic nitrogen bases; spectrophotometric method has been employed for the study of the adduct formation in a monophase chloroform. Both bidentate and unsaturated monodentate heteronuclear nitrogen bases form hexacoordinated adducts with 1:1 and 1:2 stoichiometry, respectively (metalchelate:base). However, the saturated nitrogen bases form pentacoordinated 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(00)00316-4

Spectrochimica Acta Part A 56 (2000) 2627–2635
www.elsevier.nl/locate/saa
A study of adduct formation of heterocyclic nitrogen bases
with nickel(II) chelate of
di(6-chloro-2-methylphenyl)carbazone
A.H.M. Siddalingaiah *, A.F. Dodamani, P.S. Kanavi
Department of Chemistry, Karnatak Uni6ersity, Dharwad 580 003, India
Received 29 November 1999; received in revised form 28 March 2000; accepted 28 March 2000
Abstract
The study of the adduct formation of Ni(II) di(6-chloro,2-methylphenyl)carbazonate has been undertaken by
1
synthesising and characterizing it by magnetic susceptibility, UV-VIS, IR and H-NMR spectral measurements. The
distorted square planar Ni(II) chelate forms adducts with heterocyclic nitrogen bases; spectrophotometric method has
been employed for the study of the adduct formation in a monophase chloroform. Both bidentate and unsaturated
monodentate heteronuclear nitrogen bases form hexacoordinated adducts with 1:1 and 1:2 stoichiometry, respectively
(metalchelate:base). However, the saturated nitrogen bases form pentacoordinated adducts with 1:1 stoichiometry.
The results are discussed in terms of basicity and steric factors of the bases. © 2000 Elsevier Science B.V. All rights
reserved.
Keywords: Adduct formation; Heterocyclic nitrogen bases; Basicity and steric factors
[4]. Survey of literature reveals that there are only
a few reports on some of the nuclear substituted
1. Introduction
derivatives of diphenylcarbazones and their metal
Diphenylcarbazone (DPC) is an analytical
complexes while there seem to be no reports on
reagent which can form metal complexes of high
di(6-chloro-2-methylphenyl)carbazone (abbrevi-
molar absorptivity by coordinating through the
ated as D6Cl2MPC). The study of adduct forma-
nitrogen and oxygen atoms. It has been used in
tion is of an analytical importance wherein, the
the determination of Mn [1], Cu [2] and fatty
trace amounts of Ni could be determined more
acids [3] in blood serum, as an antibacterial
precisely, particularly by the synergetic effect [5].
reagent against mycobacterium and tuberculosis
The extraction of trace amounts of Cd and Zn
using dpc through adduct formation with 1,10-
* Corresponding author. Tel.: +91-747-12115; fax: +91-
phenthroline have been reported [6]. The nickel
836-747884.
chelates of dpc and its substituted analogues en-
larges produce intense absorption in the optical
E-mail address: karuni@bgl.vsnl.net.in (A.H.M. Siddalinga-
iah).
1386-1425/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S1386-1425(00)00316-4

2628
A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 56 (2000) 2627–2635
spectra which are characteristic of the (metal-
perturbed) ligand itself. Structural changes oc-
curred in the Ni(II) chelates on adduct
formation which, therefore, gives rise to pro-
found spectral changes. The hypsochromic and
bathochromic shifts are observed in the visible
region of the spectra of Ni(II) chelates of dithi-
zone [7] and methyl substituted dpcs [8]. These
changes were employed for the determination of
adduct formation constants. Such spectral
changes also help in confirming the structure of
the pyridine adducts of the nickel chelates. Even
though lot of work has been done to study the
effect of factors such as ligand basicity, steric
effects etc. on the adduct formation of Ni(II)
chelates with substituted dithizones [7] and
quinolines, the study of adduct formation of
Ni(II) chelates of many of the substituted dpc
derivatives with nitrogen bases seems to have
not been made. In continuation of our earlier
work [9–11], we report here our studies on the
synthesis and characterization of a new deriva-
tive of dpc, viz D6Cl2MPC and its Ni(II)
chelate, viz Ni(II)-di[6-chloro,2-methylphenyl]-
carbazonate (abbreviated as Ni(6Cl2MPC)2 and
its adduct formation with nitrogen bases. An at-
tempt to study the relative importance of steric
hindrance and basicity with methyl substituted
pyridines has been made. The saturated hetero-
cyclic bases of almost of equal basicity are also
considered in this study to find out the influence
of ring size of these bases on the adduct forma-
tion.
was found out by Gouy method and the metal
estimation was done by EDTA titration method
[12].
2.2. Preparation of D6Cl2MPC
D6Cl2MPC was synthesised by a method de-
scribed earlier [13,14]. Di(6-chloro,2-methyl-
phenyl)carbazide was first prepared by heating a
mixture of 6-chloro,2-methylphenylhydrazine
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 was
dissolved in a mixture of 60 ml glacial acetic
acid, 20 ml of 1 N sulfuric acid and 2–3 drops
of 10% ferric alum and oxidised by adding 20
ml of 0.06 M potassium persulfate (K2S2O8)
dropwise with vigorous stirring for about 30
min. The resulting carbazone was extracted with
ether, washed washed several times with water,
evaporated dried and purified by column chro-
matography using a silica gel (60–120 mesh)
column. A mixture of Me2Co:CHCl3 (1:4) is
used as an eluent: yield, 58%; m.p., 142–143°C.
2.3. Reagents
Pyridine (Fisher), picolines (Eastman), lutidi-
nes, collidines, ethylenediamine (BDH) were
dried over KOH and distilled to get pure sam-
ples. Pyrrolidine, piperidine, morpholine (BDH)
and hexamethylneimine (Sigma) were purified by
refluxing over bariumoxide for 20–24 h. The
amines were fractionally distilled to get pure
samples. 2,2%-bipyridyl (Eastman). 1,10-Phenan-
throline. (G.F. Smith and Co.), 2,9-Neocuprine
(BDH), cyanopyridines (Fluka) and nickel chlo-
ride (Fisher, AR grade) were used as received.
2. Experimental
2.1. Apparatus
Absorbances were measured on Hitachi 150-
20 UV-VIS spectrophotometer. Elemental analy-
sis was carried out on Perkin-Elmer 240 CHN
analyser. IR and 1H-NMR spectra were
recorded on Nicolet-170 FTIR spectrometer and
VXR 300s Varian spectrometer, respectively.
The magnetic moment of the Ni(II) complex
2.4. Preparation of Ni(6Cl2MPC)2 complex
About 1 g of nickel chloride was dissolved in
an acetate buffer (pH 6.2) and added to an al-
coholic solution (0.01 M) of D6Cl2MPC drop-
wise at room temperature. The mixture was
stirred for about 30 min and the resulting pre-

A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 56 (2000) 2627–2635
2629
of Ni(6Cl2MPC)2 with 2,2%-bipyridyl is shown in
Fig. 2.
3. Results and discussion
3.1. Characterization of D6Cl2MPC and
Ni(6Cl2MPC)2
The elemental analyses of the ligand and the
complex, along with the magnetic data are re-
ported in Table 1. The C, H, N and metal analy-
ses confirm that the stoichiometry of the complex
is 1:2 for metal to ligand. The complex is air
stable, non-hygroscopic and soluble in non-polar
solvents. It is dark blue in colour. The subnormal
magnetic moment (2.31 BM) of the chelate may
be attributed to mixed stereochemistry around
nickel(II) [16].
Fig. 1. (a) Structure of the D6Cl2MPC. (b) Structure of
Ni(6Cl2MPC)2.
cipitate was collected under suction and washed
several times with water. The complex was dried
over P2O5 under vacuum at room temperature
and purified by Soxhlet method [15]: m.p.,
229–230°C (decomposes).
3.2. IR spectra
The IR spectra of the ligand and the complex
were recorded in 4000–400 cm−1 range. The lig-
and showed bands at 3301, 3110 and 3035 cm−1
which may be attributed to the intermolecular
bounded (ꢀNꢀH) vibrations. The bands at 1684
cm−1 and 1573 cm−1 are assigned to (ꢀCꢁO)
stretching and (ꢀNꢀH) deformation, respectively.
The disappearance of (ꢀCꢁO) stretching band at
1684 cm−1 in the spectra of the nickel complex
indicates that oxygen atom of the ligand is in-
volved in the coordination with the metal through
the enolic form. This was further confirmed by the
appearance of a band at 1505 cm−1 due to
(ꢀCꢁN) stretching in the spectra of the complex.
The IR peaks of both the ligand and the com-
plexes are given in Table 2.
2.5. Measurement of absorbances
Known volumes of chloroform solution of the
above nickel complex was pipetted into 10 ml
standard flasks containing different amounts of
nitrogen bases (dissolved in chloroform) of known
concentration. The mixtures in the flasks were
diluted to the mark with the solvent. The ab-
sorbance spectra were measured in the visible
region around 400–700 nm with an optical path
length of 10 mm and using chloroform as a
reference. The absorbance at 634 nm was consid-
ered for analysis. A typical spectra of the adduct
Table 1
Analytical magnetic data of the ligand D6Cl2MPC and Ni(6Cl2MPC)2
Compound
Found (calculated) (%)
Molecular formula
veff (BM)
C
H
N
M
D6C/2MPC
Ni(6Cl2MPC)2
53.34 (53.43)
59.24 (49.28)
4.10 (4.18)
3.50 (3.59)
16.41 (16.62)
15.40 (15.33)
–
C15H14N4OCl2
Ni(C30H26NO2Cl4)
–
2.31
8.06 (8.03)

2630
A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 56 (2000) 2627–2635
Table 2
IR frequencies (cm−1) of the ligand D6Cl2MPC and Ni (6Cl2MPC)2
Compound
(NꢀH)
(CꢁO)
(NꢀH)
(CꢁN)
(CꢁC)ar
(CꢀO)
(NꢀH) (bend)
D6Cl2MPC
Ni(6Cl2MPC)2
3301, 3110, 3035
2937
1684
–
1578
1573
–
1505
1486
1462
–
763
780
1200, 1165, 1098
1
3.3. H-NMR spectra
472 and 580 nm for Ni(6Cl2MPC)2 adduct sys-
tems, the measurements at 634 nm is more suit-
able for analysis since the difference in
absorbance between the chelate and adduct is the
largest at this value. Therefore, absorbance value
at 634 nm were plotted as a function of −log [B]
to get sigmoidal curves. Ach, Aad, A and −log [B],
values were used for the calculation of log inad
using Eq. (1):
The 1H-NMR spectrum of the ligand was
recorded using CDCl3 as solvent and the TMS as
an internal reference. The two sharp singlets at l
2.35 and 2.76 are due to two non-equivalent –
CH3 groups. The two broad peaks at l 6.13 and
8.2 are due to aniline –NH and amide –NH
groups, respectively. The multiplets observed in
the region l 6.76–7.70 may be attributed to six
aromatic hydrogen atoms. The data is given in
Table 3.
log iand= −n log [B]+log [(Ach−A)/(A−Aad)]
(1)
From the elemental and spectral analyses the
structures of D6Cl2MPC and Ni(6Cl2MPC)2 may
be confirmed as shown in Fig. 1(a and b),
respectively.
where ‘n’ is the number of base adducts ‘B’,
attached to the chelate. Ach and Aad are the ab-
sorbances due to chelates and adducts, respec-
tively while ‘A’ is the absorbance due to the
chelate–adduct equilibrium mixture.
3.4. Adduct formation study
For adduct formation from Ni(6Cl2MPC)2
with unsaturated monodentate bases such as pyri-
dine, methyl pyridines and cyanopyridines, the
adducts were found to contain two moles of bases
per chelate molecule as indicated by the slope 2 in
the plots of log [(Ach−A)/(A−Aad)] versus −
log [B]. This indicates hexacoordinated adducts
with 1:2 chelate:base stoichiometries. It is interest-
ing to note that Ni(6Cl2MPC)2 adducts with pyri-
dine, 3-picoline, 4-picoline and 3,4-lutidine are
unstable and decolorize rapidly whereas those
with 2-picoline, 2,4-lutidine and 2,4,6-collidine
which have sterically hindered groups are stable
for at least 1 h. The formation of stable adducts
by 2-picoline, 2,4-lutidine and 2,4,6-collidine may
The spectrum of pure chloroform solution of
Ni(6Cl2MPC)2 shows two absorption bands in
the visible region at around 464 and 634 nm
(m464=3.2×104 l mol−1 cm−1 and m634=4.0×
104 l mol−1 cm−1), respectively. The spectrum of
Ni(6Cl2MPC)2 undergoes a profound change on
addition chloroform solution of an heterocyclic
bases and the absorption bands of the chelate
collapse into a single band at around 518 nm. It
was also noticed that greenish blue colour of the
chelate solutions in chloroform change to pink
upon the adduct formation. Though there are two
isosbestic points in the visible region at around
Table 3
1H-NMR spectra of ligandsa
Compound
D6Cl2MPC
Methyl (ꢀCH3)
Phenyl-NH
6.13 (br)
Amide-NH
8.2 (br)
Aromatic H
2.35 (s), 2.76 (s)
6.76–7.70 (m)
a Chemical shifts in ppm (l).

A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 56 (2000) 2627–2635
2631
be attributed to their increased basicity which
deminates over steric effects. In the case of bases
forming unstable adducts, the adduct formation
constants could not be determined. 3-Cyano and
4-cyanopyridine from stable adducts with the
nickel chelate (Fig. 4). The log iand values of the
4-cyanopridine adduct, are higher than those of
the 3-cyanopyridine adduct, because the cyano
group in the fourth position will tend to withdraw
electrons from the nickel(II) ion into the ring or,
in other words, increase the double bond charac-
ter. Groups in the three position cannot con-
the stability of these adducts increases as the
basicity of nitrogen base increases.
The monodentate pyridine bases form 1:2 hexa-
cordinated adducts with Ni(6Cl2MPC)2 as shown
by the slope of 2 in the plots of log [(Ach−A)/
(A−Aad)] versus −log [B]. The order of stability
of these adducts follows the expected steric
hindrance and basicity of the adducting bases.
Thus 2-picolineB2,4-lutidineB2,4,6-colidineB
pyridine B 3-picoline B 4-picoline B 3,4-lutidine.
The following is the stability order for cyano- and
methylpyridine adducts: 3-cyanopyridineB4-
cyanopyridineB3-picolineB4-picoline. This fol-
lows the expected resonance and substitution
effects of the bases.
tribute to this type of resonance [17].
A
comparison of the stability of cyanopyridine ad-
ducts with those of methylpyridines is not possi-
ble, since the bases of the latter form unstable
adducts with nickel(II) chelates under study.
The log iand values of Ni(6Cl2MPC)2–
methylpyridine adducts lie in the following order:
Pentacoordinated adducts were obtained with
saturated heterocyclic bases with 1:1 stoichiome-
try. The adduct constant formation constants of
Ni(II) chelate decrease when the ring sizes of the
nitrogen bases increase from five-membered
2-picolineB2,4-lutidineB2.4,6-collidine.
Thus
Fig. 2. Absorption spectra of Ni(6Cl2MPC)2+2,2%-bipyridyl mixture in CHCl3[Ni(6Cl2MPC)] 1.4325×10−5 M:[2,2%-bipyridyl]
10−6 M. (a) 0.00; (b) 0.10; (c) 0.20; (d) 0.30; (e) 0.40; (f) 0.50; (g) 0.60; (h) 0.70; (i) 0.80; (j) 0.90; (k) 1.00; (l) 1.20.

2632
A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 56 (2000) 2627–2635
Fig. 3. Mole ratio plots of the adduct of Ni(6Cl2MPC)2+2,2%-bipyridyl 2,9-neocuprine bases in CHCl3.
pyrrolidine to seven-membered hexamethylenei-
mine ring although their pKa values are almost
the same. Therefore, steric effects are found to
be more important in the formation of adducts
in these cases. The smaller formation constant
of the adduct of Ni(II) chelate with morpholine
may be attributed to the decreased basicity of
the nitrogen atom in the morpholine ring.
Strong bases however will form 1:1 adducts and
the formation of 1:2 adducts is not possible due
to steric hindrance by the substituents on the
chelate rings which are no longer planar [18].
Further, the chelate rings will be disrupted due
to the higher basicity of donor nitrogen atom.
There is a strong interaction between the nickel
atom in [Ni(6Cl2MPC)2] and pyrrolidine, pipe-
ridine, hexamethylnimine, and morpholine as a
result of which the available positive charge on
the nickel atom decreases and there by the ten-
dency for the axial addition of a sixth ligand to
the nickel atom is reduced (Fig. 5). This type of
electrostatic effect is enhanced by a steric effect
such that the approximately coplanar chelate
rings are distorted by the addition of the first
axial ligand so as to sterically hinder the trans
additions of another axial ligand [19]. Hence,
when strong bases are used to form adducts
with planar metal chelates, 1:1 adducts will be
formed almost exclusively (Fig. 6).
From the study of adduct formation of Ni(II)
chelate with saturated heterocyclic bases, it is
clear that the structural and electrostatic rear-
rangements in the donor as well as in the accep-
tor molecules must be considered in the
interpretation of adduct formation [20]. Fer-
nando [21] has shown that there is a consider-
able distortion in the Ni(II) chelates when
adducts are formed with strong nitrogen bases.
The donor molecules themselves must undergo
structural changes [22]. For example, piperdine,
in chair configuration has the hydrogen on ni-
trogen atom in the equatorial position when ad-
duct formation occurs, the hydrogen atom
probably shifts to the axial position to allow the
nickel atom to bond to the nitrogen and occupy
the equatorial position. The order of stability of
these adducts is: morpholineBhexa-methylenei-
mineBpyrrolidineBpiperidine. Thus, the order
follows the electrostatic and steric variance of
the bases [18].

A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 56 (2000) 2627–2635
2633
Fig. 4. Sigmoidal plots for the adducts of Ni(6Cl2MPC)2 monodentate bases in CHCl3: 2-picolene, 2,4-lutidine, 2,4,6-colidine,
3-cyanopyridine, 4-cyanopyridine.
Fig. 5. Sigmoidal plots for the adducts of Ni(6Cl2MPC)2 monodentate bases in CHCl3: pyrrolidine, piperidine, hexamethyleneimine,
morpholine.

2634
A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 56 (2000) 2627–2635
Fig. 6. Linear plots for the adducts of Ni(6Cl2MPC)2 monodentate bases in CHCl3.
Table 4
From the formation of almost equally stable
adducts in the case of bidentate bases such as
2,2%-bipyridyl, 1,10-phenanthroline etc. it appears
that the adduct formation is not adversely influ-
enced by the steric effects. This might be due to
the rearrangement of chelate rings in order to
provide a cis position for the bidentate adduct-
ing bases [23]. 2,9-Neocuproine forms a less sta-
ble adduct due to the steric hindrance offered
by the methyl groups. The stoichiometry of
these adducts were confirmed by mole ratio
Adduct formation constants of nitrogen bases with Ni(II)
chelate of D6Cl2MPC
Base
pKa
5.20
5.90
5.68
6.08
6.72
6.52
7.48
–
Slope (n)a
Log iand
Pyridine
2-Picoline
3-Picoline
4-Picoline
2,4-Lutidine
3,4-Lutidine
2,4,6-Collidine
3-Cyanopyridine
4-Cyanopyridine
Pyrrolidine
Piperidine
Hexamethyleneimine
Morpholine
2,2%-Bipyridyl
1,10-Phenanthroline
2,9-Neocuproine
Ethylenediamine
ID
2
ID
ID
2
ID
2
2
2
1
1
1
–
1.82
–
–
1.90
–
2.18
1.57
1.78
2.90
2.50
2.30
1.47
5.05
5.00
4.96
5.10
method.
The
mole
ratio
plots
for
–
Ni(6Cl2MPC)2–2,2%-bipyridyl
2,9-neocuproine
11.27
11.00
11.07
8.35
4.40
4.95
5.85
6.84
adducts system are shown in Fig. 3. The experi-
mental results given in Table 4.
1
1b
1b
1b
1b
Acknowledgements
A.F. Dodamani wishes to express sincere
thanks to the Chairman, Department of Chem-
istry, Karnatak University, Dharwad for provid-
ing the necessary facilities.
a n is the number of base molecules per chelate.
b The value obtained from mole ratio plot. Slope=1 means
1:1 ratio and slope=2 means 1:2 ratio for Ni chelate to base.
ID, instantaneously decolourized.

A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 56 (2000) 2627–2635
2635
References
don, 1959, p. 79.
[13] A.H.M. Siddalingaiah, M.Y. Kariduraganavar, Asian J.
Chem. 7 (3) (1995) 621.
[14] A.H.M. Siddalingaiah, M.Y. Kariduraganavar, Asian J.
Chem. 8 (2) (1996) 183.
[15] A.I. Vogel, Text Book of Practical Organic Chemistry,
3rd ed., Longmon Press, London, 1964, p. 153.
[16] T.S. Kannan, A. Chakravorti, Inorg. Chem. 9 (1970)
1153.
[1] D. Soldatovic, G. Farah, Arh. Farm. 24 (1974) 129.
[2] L.N. Lapin, N.V. Reis, Lab. Delo. 3 (1977) 175.
[3] H. Kushiro, Y. Takano, H. Soyama, I. Fukui, Rinsho
Eyori. 18 (1970) 451.
[4] E. Schraufstatter, Z. Naturforsch 5b (1950) 190.
[5] T. Suresh, V.H. Kulkarni, Asian J. Chem. 6 (3) (1994)
690.
[17] R.K. Murmann, F. Basolo, J. Am. Chem. Soc. 77 (1995)
3484.
[6] E. Yamada, E. Nakayama, T. Kuwamoto, Fujinaga, Bull.
Chem. Soc. Jpn. 55 (10) (1982) 3151.
[18] P. Jose, S.S. Coi, Q. Fernando, J. Inorg. Nucl. Chem. 31
(1971) 1969.
[19] M. Nanjo, T. Yamasaki, J. Inorg. Nucl. Chem. 32 (1970)
2411.
[7] K.S. Math, H. Freiser, Anal. Chem. 41 (1969) 1682.
[8] K.S. Math, T. Suresh, Talanta 32 (1985) 811.
[9] A.H.M. Siddalingaiah, R.B. Bhat, Asian J. Chem. 7 (8)
(1996) 761.
[20] T. Marshal, Q. Fernando, Anal. Chem. 44 (1972) 1346.
[21] Q. Fernando, Separ. Sci. 1 (1969) 575.
[22] A.F. Garito, B.B. Wayland, J. Am. Chem. Soc. 91 (1969)
866.
[10] A.H.M. Siddalingaiah, R.B. Bhat, Trans. Met. Chem. 21
(1996) 327.
[11] A.H.M. Siddalingaiah, R.B. Bhat, Trans. Met. Chem. 22
(1996) 105.
[12] H.A. Flaschka, EDTA Titrations, Pergamon Press, Lon-
[23] K.S. Math, H. Freiser, Chem. Comm. 110 (1970).
.